Document text
FM 34-81-1
FIELD MANUAL DEPARTMENT OF THE ARMY
FM 34-81-1 Washington, DC, 23 December 1992
BATTLEFIELD WEATHER EFFECTS
Table of Contents
Page
PREFACE iii
INTRODUCTION v
CHAPTER 1 - Combat Environment 1-1
Weather and the Commander 1-1
Weather Tactical Decision Aids 1-3
The Battlefield and the Environment 1-3
CHAPTER 2 - Weather Elements and Support 2-1
Interaction of Battlefield Environment 2-1
Elements
Weather Products 2-5
Sources of Weather Support 2-7
Terrain Analysis Team Support 2-1 1
Use of Intelligence Preparation of the 2-1 1
Battlefield Templates
CHAPTER 3 - Commander's Weather Information Requirements 3-1
Forecasts, Outlooks, and Reports 3-1
Establishing Requirements for Forecasting 3-2
Support
Receipt of Forecasts 3-7
CHAPTER 4 - Weather Tactical Decision Aids 4-1
Explanation and Presentation 4-1
Use of the Appendixes 4-2
The Weather Briefing 4-3
DISTRIBUTION RESTRICTION: Approved for public release; distribution is unlimited.
FM 34-81-1
APPENDIX A - How to Use the Tables and Type Unit A-1
Reference Tables
APPENDIX B - Weather Effects on Air Defense Artillery B-1
APPENDIX C - Weather Effects on Arnnor C-1
APPENDIX D - Weather Effects on Artillery D-1
APPENDIX E - Weather Effects on Aviation E-1
APPENDIX F - Weather Effects on Electro-Optical Systems F-1
APPENDIX G - Weather Effects on Engineers G-1
APPENDIX H - Weather Effects on Light Infantry H-1
APPENDIX I - Weather Effects on Intelligence 1-1
and Electronic Warfare
APPENDIX J - Weather Effects on Mechanized Infantry J-1
APPENDIX K - Weather Effects on Nuclear, Biological, K-1
and Chemical Operations
APPENDIX L - Weather Effects on Personnel L-1
APPENDIX M - Weather Effects on Special Operations Forces M-1
APPENDIX N - Part I - Weather Effects on Threat Systems N-1
Part 11 - Comparison of Weather Effects on US
and Threat Systems N-9
APPENDIX - Weather and Environmental Elements and 0-1
Parameters Impacting Army Systems
and Operations
APPENDIX P - Conversion Factors P-1
GLOSSARY Glossary-1
REFERENCES References-1
INDEX lndex-1
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FM 34-81-1
PREFACE
This manual provides some of the more common critical weather (and
environmental) effects data and applies that information to specific operations,
systems, and personnel. Inclement weather degrades battlefield operations,
affects weapons and other systems, and plays a major role in the effectiveness of
troops in the field.
This data is intended to support the brigade and battalion S2 and staff. It is
applicable to combat, combat service, and combat service support units and is
intended for use by Active Component (AC), Reserve Components (RC), and Army
National Guard (ARNG) units in both training and combat situations.
Use of these lookup tables and data is a three-step process. For additional
information on how this is accomplished, see Appendix A. The three steps are~
• Using current weather observations and forecasted
conditions, you look for weather extremes. That is, those
conditions that will be too hot, too cold, too windy, too
overcast, too wet, or too humid for normal operations.
• Turning to the lookup tables, you then identify specific
operations, systems, and personnel that will be impacted.
• And finally, bringing any impacts and constraints you have
identified to the attention of your commander and the rest of
the staff.
The critical values presented here, together with current weather
observations or future forecasts mentioned above, will provide you with the basic
tools needed to perform these three steps. Data are presented in the form of
simple lookup tables called weather tactical decision aids (WTDAs). These WTDAs
are designed to point you toward your briefing of the commander and staff.
Appendixes B through O are tailored toward specific types of units.
This manual does not make you an expert in all facets of weather and the
total impact that inclement weather might have on an army in the field. Instead, it
allows you to quickly understand the potential impact specific current and
forecasted weather elements could have on your unit's plans today.
Not all weather and environmental data parameters impacting Army systems
and operations are addressed. A listing of the weather and data parameters
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INTRODUCTION
ACT 3, SCENE 2. Location: Second floor of 3d Army Headquarters Building,
European Theater of Operations, Germany. Date: December 1944. Players:
General George Patton and Army Chaplain Colonel James H. O'Neill. Patton
speaks . . .
"Chaplain, write me a weather prayer."
This prayer was subsequently issued, along with a Christmas card, to all 3d
Army troops on December 22, 1944. In part, it read:
"Almighty and merciful Father . . . restrain these immoderate rains . . . grant us
fair weather for battle ..."
And, of course, as history has so well recorded, "December 23 dawned bright
and sunny. " A miraculous 5-day break of clear weather followed, which permitted
the Allied forces to take maximum advantage of their air superiority. This
tremendously successful air support effort was one of the key factors that led to
the German failure to attain its major objectives in the Battle of the Bulge.
Other historical accounts state that General Patton actually ordered his
Chaplain to write this prayer in support of an earlier operation against the Siegfried
Line. Nevertheless, it wasn't used until December 22, 1944.
This dramatic acknowledgment of the importance of weather on military
operations is from the book Lucky Forward - The History of Patton' s Third U.S.
Army by Colonel Robert S. Allen (Vanguard Press, New York, 1947).
A half century later the same urgent concern about weather is reflected in
FM 100-5 where weather is listed among the imperatives of battlefield operations.
In addition, FM 100-5 states that weather and visibility conditions create
advantages and disadvantages for combat forces. To fight effectively,
commanders must acquire weather information about their entire areas of
operations (AO) and areas of interest (AI).
As the S2, that is your job. Because we cannot count on a weather prayer to
always supply this essential information to the commander, we need procedures
that will provide accurate, timely, and tailored weather data to the commander.
FM 34-81-1
Since we cannot control the weather, the best alternative is to develop a
thorough understanding of weather effects and their impact on friendly and threat
military operations. Then we use this knowledge and information to our
advantage.
Chapters 1 , [2[ and [sj provide backgro und inform ation on weather and its
effects on Army sys tems and oper ations. [Chapter 4| explains the use of the
WTDAs contained in Appendixes B through IN
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currently ide ntified as impacting Army operations, systems, or personnel is at
Appendix O
If you determine that a weather element may have a severe or moderate
impact on operations, systems, or personnel (friendly or threat), you alert the
commander and staff to this potential impact. This allows your commander to~
Request additional information.
Modify his plans.
Continue as originally planned, but aware of potential
weather problems.
The proponent of this publication is the United States Army Intelligence
Center and Fort Huachuca (USAIC&FH). USAIC&FH is the proponent for Army
weather minus Field Artillery. Send comments and recommendations on DA Form
2028 (Recommended Changes to Publications and Blank Forms) directly to
Commander, US Army Intelligence Center and Fort Huachuca, ATTN: ATZS-TDL-D,
Huachuca, AZ 85613-6000.
This manual does not implement any International Standardization
Agreements.
Unless this publication states otherwise, masculine nouns and pronouns do
not refer exclusively to men.
IV
FM 34-81-1
CHAPTER 1
COMBAT ENVIRONMENT
Weather, terrain, and the time of day constitute the basic environmental
setting for all military operations. These physical conditions affect operations,
systems, and personnel and act as constraints on the combat options available to
your commander. Part of your job is to alert your commander and the staff of the
implications adverse weather may have on both friendly and threat tactics,
techniques, and procedures (TTP).
WEATHER AND THE COMMANDER
FM 100-5 states that terrain and weather affect combat more than any
other physical factors. Weather not only affects battlefield operations, weapons,
and electronics systems but also affects the soldiers that make it all work.
Commanders cannot control the weather, but they must be sensitive to the effects
inclement weather has on their unit.
In your role as the brigade or battalion staff officer with primary
responsibility for weather intelligence and planning, you may not be Patton's
chaplain. But you have an even more important task than writing a weather
prayer— that of keeping your commander informed of adverse weather problems.
And in order to do this, you need to be familiar with weather terminology and the
collection, forecasting, and reporting available to your command.
Separate and aviation brigades, armored cavalry regiments (ACRs), special
forces groups (SFGs), and divisions and above have a United States Air Force
(USAF) staff weather officer (SWO) and weather team (WETM). Their job is to
collect, analyze, and advise the senior intelligence officer (SIO) of current and
forecasted weather conditions which will affect operations.
At maneuver (and other) brigades and battalions, you have no SWO. It is
therefore very important that you familiarize yourself with the observations,
forecasts, and other services provided by SWOs and WETMs at higher echelons.
You need a general working knowledge of meteorology and an understanding of
this manual. The simple WTDAs presented here help you in putting several pieces
of the weather puzzle together. They then aid you in translating weather
information into a format understandable to your commander and staff.
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BATTLEFIELD ENVIRONMENT
Battlefield environmental conditions play a major role in the application of
TTP. Some of the environmental factors evaluated in this manual are-
General weather conditions.
Terrain effects.
Battlefield-induced contaminants (BIC).
Illumination.
Background signatures.
Hazardous or severe conditions.
Evaluation of each of these factors is essential during your commander's
decision-making process. All must be considered together i n your ana.
ysis because
for an
they all impact each other—and friendly and threat TTP. See [Chapter 2
explanation of weather factors and their interplay with each other. [Chapter 3
helps you translate current weather conditions and future forecasts into valuable
intelligence.
WEATHER ELEMENTS AND CRITICAL VALUES
Weather elements, and their associated impacts on battlefield operations, are
the primary focus of this manual. Only the more commonly known, observed, or
derived weather and environmental elements are discussed. A working knowledge
about these elements is essential. Even more important is knowing when, and to
what degree, these elements act as constraints on specific systems or operations.
These thresholds (or amounts) are called critical values and listed for each
weather or environmental element. They are based on input from battlefield
functional area (BFA) proponents, available data from third-party sources. Army
field manuals, and the systematic analysis of weather-induced degradation of
operations, systems, and personnel.
Weather and environmental data elements, in addition to those discussed
here, may impact Army systems and operations. But the capability to collect and
process them, or to technically define their impact, is presently limited. We are
developing automated initiatives to identify and collect more weather and
environmental data. These findings will be incorporated into subsequent iterations.
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WEATHER TACTICAL DECISION AIDS
WTDAs provide tailored decision information to the user. They may be a
simple two-sided matrix or lookup tables (as used in this manual), or complex
software algorithms requiring computer processing. These tables assist you in
matching a particular inclement weather condition with its associated impact on
the battlefield. This correlating process is helped along by the WTDAs.
Lookup tables show the impact of critical weather and environmental
elements on battlefield operations, systems, and personnel. Remember that these
examples do not cover every battlefield situation, condition, or system. You may
have to add others to cover any unique items in your unit.
If you are tasked to provide information for weather parameters not normally
provided by the WETM, first determine what the critical values are for the system
or operation. Your S3 should be able to assist you in analyzing the equipment and
determining weather effects GO, NO-GO thresholds. Your nearest SWO (probably
at division) can provide the additional weather data support.
You need to keep in mind that much computer-driven automation is coming
to the battlefield. Some of these initiatives will affect the collection, processing,
and dissemination of weather forecasts and weather effects predictions. They
include the All-Source Analysis System (ASAS), the Integrated Meteorological
System (IMETS), the Digital Topographic Support System (DTSS), and the Army
Tactical Command and Control System (ATCCS). These initiatives will result in
more precise data being quickly passed to the users so weather considerations will
keep pace with the decision-making cycles of commanders.
THE BATTLEFIELD AND THE ENVIRONMENT
FM 100-5 is the umbrella concept for combat operations and the baseline
document that describes warfighting doctrine. All other specific mission
operations manuals spring from FM 100-5. It describes how the Army fights and
wins on the battlefield. It lists three different types of battlefields on which the
Army must be prepared to fight: high-intensity conflict (HIC), mid-intensity conflict
(MIC), and low-intensity conflict (LIC).
DISPERSED OPERATIONS
FM 100-5 describes these conflicts as being characterized by dispersed
operations employing sophisticated, longer range, and more lethal weapons
systems. The scope of the battle is dramatically increased because of these
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systems and results in improved battlefield surveillance, more effective target
acquisition sensors, and flexible communications links.
Command and control (C^) is critical to success. Interruption of
communications with higher headquarters and adjacent units can destroy
synchronization and control. The effective control of airspace is a leading factor in
the outcome of battles. High consumption of supplies, rapid movement, and long
(therefore vulnerable) lines of communication (LOC) will challenge communicators
and logisticians.
Overlaid on all of these concerns is the major constraint the environment
plays on the battlefield. These are serious environmental constraints which, in
turn, influence your commander's ability to apply maximum combat power at the
right time and place.
A good example of using inclement weather effects to an advantage was
demonstrated by the Soviets during World War II. They used weather to maximize
firepower. Whenever heavy precipitation was expected, they moved their artillery
to defilade positions close to the front lines.
After the storm, mobility was usually impossible and the Russians delivered
rapid and accurate indirect fire on the immobilized Germans.
PROTECTION OF THE FORCE
Protection of the force against adverse effects of weather is paramount to
maintaining maximum warfighting capability— and one of your biggest and most
important tasks.
Protection of the force and understanding the impact of adverse weather can
be quickly illustrated by an incident from the Korean War in early 1951. A
battalion-sized relief-in-place was planned for late afternoon. The location was on
the top of a 1,500-meter hill. The temperature at the time of the relief was nice
and warm and the operation was conducted by troops wearing summer-like
clothing. No plans had been made to issue winter clothing that evening because
no one took the time to look at the weather forecast.
During the night a cold front forced temperatures below freezing. Cold
weather injuries to 75 percent of the personnel made the unit completely
ineffective. Intelligent planning, including a weather forecast, could have avoided
the injuries and maintained full warfighting capability.
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The protection of your force requires that you understand and identify
inclement weather impacts on friendly and threat capabilities for the commander.
It is your responsibility to inform him, and other staff planners, of current or
forecasted weather conditions that endanger unit success. Accurate weather
effects information is a major key to successful military operations.
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CHAPTER TWO
WEATHER ELEMENTS AND SUPPORT
A working knowledge of various weather elements identified here is
essential to your ability to provide your commander with a complete picture of
potential adverse weather effects on the battlefield. But, you are not alone in your
mission. Help is available from a variety of sources.
INTERACTION OF BATTLEFIELD ENVIRONMENT ELEMENTS
Weather conditions, terrain, BIC, illumination, and background signatures are
some of th e primary conditions that will be found in a battlefield environment.
Table 2-1 defines some of the more common weather elements discussed.
A weather element generally is an atmospheric variable that is measured in a
weather observation. A weather parameter is derived from one or more weather
elements. For example: density altitude is a weather parameter derived from the
elements barometric pressure and temperature.
You must remember that weather conditions such as wind, precipitation,
and clouds can impact or can be influenced by the other conditions of the
battlefield (terrain, BIC, illumination, and background signatures). All of these
conditions are interdependent to a certain degree and must be considered as a
whole, and not each in isolation.
WEATHER EFFECTS AND TERRAIN
Terrain features affect such weather elements as visibility, temperature,
humidity, precipitation, winds, and clouds. The most common example of terrain
affecting weather is that on the windward side of high terrain, such as mountains,
the rainfall rate will be greater than on the leeward (opposite) side.
On the other hand, weather conditions such as temperature, winds, and
precipitation have a definite effect on the terrain and can enhance or limit military
operations, such as trafficability, watercrossing (fording), and the first-round
accuracy of supporting field artillery fires. The responsibility for determining
mobility and counter-mobility is given to the terrain team at division.
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Table 2-1. Common weather elements.
ATMOSPHERIC PRESSURE: Atmospheric pressure is the pressure exerted by the atmosphere at a given point and
measured by a barometer in inches of mercury (Hg) or in millibars (Mb).
Pressure Altitude: This is indicated in an altimeter when 29.92 is set in the barometric scale
window. High pressure altitude is critical to the lift capability of fixed wing
aircraft.
Density Altitude: This is a place in the atmosphere corresponding to a particular value of air density.
High pressure is critical to helicopter operations.
CLOUDS: The amount of sky covered by clouds is usually described in eighths. Overcast (8/8ths), broken
(5 to 7/8ths), or scattered (1 to 4/8ths). Cloud conditions are described by the amount of cloud cover and the height
of the base of the cloud above ground level. A cloud ceiling is the height of the lowest broken or overcast layer, and is
expressed in feet. A higher layer of several scattered layers of clouds is designated as a cloud ceiling when the sum of
the coverage of the lower layers exceeds 4/8ths.
DEW POINT TEMPERATURE: Dew point is the temperature to which the air must be cooled for the air to become
saturated and allow dew, and probably fog, to form.
HUMIDITY: This is the state of the atmosphere with respect to water vapor content. It is usually expressed as:
Relative Humidity: This is a ratio between the air's water content and the water content of saturated
air.
Absolute Humidity: This is a measure of the total water content in the air. It is high in the tropical
ocean areas and low in the arctic.
PRECIPITATION: Precipitation is any moisture falling from a cloud in frozen or liquid form. Rain, snow, hail, drizzle,
sleet, and freezing rain are common types. The intensity of precipitation is described as light, moderate, and heavy.
Light Rain: Drops are easily seen, very little spray, and puddles form slowly, and
accumulation is a trace to 0.10"/hour.
Moderate Rain: Drops are not easily seen, spray noticeable, puddles form rapidly, and
accumulation rates are 0.1 1" to 0.30"/hour.
Heavy Rain: Drops are not seen, rain comes in sheets with heavy spray, puddles form quickly,
and the rate is more than 0,30'7hour.
Light Snow: Visibility is equal to or greater than 5/8 miles, or 1 ,000 meters in falling snow; and
a trace to 1 inch/hour accumulates.
Moderate Snow: Visibility is 5/16 to 1/2 statute miles, or 500 through 900 meters in falling snow
with 1 to 3 inches/hour accumulation.
Heavy Snow: In heavy snow, visibility is cut to less than 1/4 statute miles, or 400 meters, with
more than 3" accumulation/hour.
TEMPERATURE: Temperature is the value of heat or cold recorded by a thermometer normally at 6 feet above the
ground at the observation site. Temperatures are normally given in both Fahrenheit and Celsius values. It is sometimes
referred to as the ambient air temperature.
VISIBILITY: A measurement of the horizontal distance at the surface or aloft that the unaided human eye can discern
a large object or terrain feature. Visibility is reported in meters or fractions of a mile, and is reported as a prevailing value
of the visibility in all directions. Thus, a visibility report of 1,600 meters may not reveal that fog is diminishing visibility
to 400 meters in the northwest if the observer has good visibility in other directions. However, such an event would
typically be carried in the weather observation's remarks section.
WIND SPEED AND DIRECTION: These two measure the rate of movement of the air past a given point and the
direction from which the wind is blowing. A gust is a rapid fluctuation in wind speed with a variation of 10 knots or more
between peak and lull. Gust spread is the instantaneous difference between a peak and a lull and is important for
helicopter operations.
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Examples of terrain products that are normally prepared and available from
the division terrain analysis team for use in the intelligence preparation of the
battlefield (IPB) are discussed later in this chapter in the terrain analysis team
support section.
BATTLEFIELD-INDUCED CONTAMINANTS
During combat operations, visibility can become severely reduced by BIC.
These contaminants are either induced directly by combatants or occur as
by-products from battlefield operations.
Two significant sources of battlefield contaminants are dust produced by
high explosive (HE) artillery or mortar rounds and deliberately employed smoke. HE
rounds used in a pre-attack barrage may not only kill enemy forces, but also may
restrict the visibility of your own troops by dust caused by the HE if the direction
of the wind is not taken into account. Smoke produced by smoke generators,
vehicle exhaust emission systems, smoke pots, indirect fire, and smoke rounds
also obviously produce battlefield contaminants.
Wind speed and direction are critical to maintaining an effective smoke
screen. Rain can remove BIC quickly. Weather inversions over valley areas can
sustain airborne contaminants for long periods of time.
Other sources of BIC that will lower visibility in the AO are clouds of dust
from vehicle traffic or smoke from fires. These types of contaminants not only
blind you but also may help your adversary in detecting troop movements and
pinpointing your location.
A unique BIC, affecting visibility, occurs in very cold conditions when
temperatures are in the range of -30° C or -22° F or colder. Whenever a source of
moisture or water vapor is released into the cold air by internal combustion
engines, artillery fires, or launching of self-propelled munitions, visibility can be
reduced to zero when the moisture freezes instantly and changes into ice fog.
Ice fog may restrict visibility across a whole valley and, once created, can
linger for hours. Ice fog crystals permit ground objects to be seen from above
while severely restricting visibility on the ground—an advantage for aerial
reconnaissance.
On airfields an ice fog created by fixed-wing aircraft may cover an entire
runway. Visibility can be reduced so that other aircraft cannot take off or land if
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the wind is calm. Besides reducing visibility, the ice fog draws attention to the
airfield location.
Launching missiles such as the tube-launched, optically tracked, wire-guided
(TOW) in very cold air can create an ice fog. As the TOW moves to the target, the
exhaust blast exits into the air where it condenses and creates the ice fog. If the
wind is calm, this fog follows the trajectory of the missile and reduces launch point
visibility to such an extent that the operator loses sight of the target. Also, the
launch point can be identified by threat forces from the condensation trail of the
missile.
ILLUMINATION
Natural light is critical in planning operations where night vision devices
(NVD) are used or in operations timed to use only available light. Natural light
values vary as a function of the position of the sun, moon, stars, and clouds. Light
data are available from your SWO for any time, period, and place. These data are
particularly important for determining first and last light, moonrise, and moonset,
and are most effective for planning use of NVD.
Appendix F provides more detail on the impact of illumination on
electro-optical (E-0) devices. Variables such as altitude, cloud cover,
terrain-produced shadows, visibility, and direction of vehicle or aircraft movement
in relation to the sun or the moon can also affect light level availability.
Artificial light is intended to increase visibility, but, under certain weather
conditions, this does not always occur. For example: Low cloud ceilings will limit
the area covered and effective time of flares. Rain, snow, or fog can reduce flare
effectiveness. However, under the right conditions, cloud cover can enhance the
effects of artificial light due to cloud base reflection. Snow or sand covered terrain
also reflect both natural and artificial light.
BACKGROUND SIGNATURES
Temperature, wind, and precipitation have a major influence on your ability
to pick out a target from the background in the infrared spectrum. They also
affect seismic (sound and acoustic) signatures. Detection of objects in the infrared
spectrum depends on a temperature contrast between the object and its
surrounding environment. This difference is known as the background signature.
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A more detailed explanatio n on how the background signature is affected
and changed by weather is also in [Appendix F| . Snow, rain, and wind influence the
background signature because they can change the surface temperature of objects.
These elements lower object temperatures and thus reduce the differential
between a target and its background.
A heavy layer of snow produces a washout during any part of the day since
it causes both the object and the background to exhibit the same temperature.
Precipitation also degrades seismic sensors through the introduction of
background noise (rain), while a snow-covered surface will dampen sound and the
movement of troops.
OTHER WEATHER PHENOMENA
Although we have discussed such elements as clouds, temperature, and
precipitation, other phenomena should not be overlooked. For example: In the
desert, strong winds produce dust storms that can last for hours or even days.
Any wind, during cold weather, causes loss of h eat from the body and
increases the danger of freezing. This is discussed in Appendix L. Thunderstorms,
with their associated lightning, strong winds, and heavy rains affect the battlefield
environment. Owing to their short-lived ferocity and unpredictability over a given
time and location, thunderstorms are difficult to assess in planning. But when they
occur, they definitely disrupt intelligence gathering and affect personnel movement,
equipment function, and target identification.
Atmospheric pressure is essential information for aircraft operations. High
humidity and temperature affect aircraft lift and significantly reduce a soldier's
ability to work and fight.
WEATHER PRODUCTS
There are four types of weather information products that are available:
Weather Observations.
Weather Forecasts (to include severe weather warnings).
Climatology.
WTDAs.
All of these products are vital in preparing a complete weather picture of the
battlefield, and showing critical weather impacts on your unit's systems and operations.
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WEATHER OBSERVATIONS
There are two types of weather observations normally collected on the
battlefield: surface and upper air. Surface weather observations are taken by both
Army and USAF personnel. Army intelligence personnel take weather observations
under the Forward Area Limited Observing Program (FALOP) as outlined in
FM 34-81/AFM 105-4.
Participating Army personnel (usually someone on your staff) will be taking a
limited number of abbreviated surface observations, using a small, manual belt
weather kit (BWK). The BWK is scheduled for replacement by an automated
meteorological sensor system.
WETMs take and disseminate hourly observations as well as special
observations when critical changes occur. Weather observations within the
division AO might be available from a USAF mobile observing team (MOT). The
MOTs are organic to the division WETM and are deployed at the direction of the
SWO after coordination with the G2. If the G2 decides against employing a MOT
below the division main command post (CP), the only immediate source of weather
observations at the maneuver brigade and battalion are from the FALOP.
Regardless of the source of weather observations, they reflect current
conditions and could be used, if the weather is stable, as an indicator for up to
1 to 3 hours. Remember that as the quality and quantity of observations diminish,
their value, as even near-term trend indicators, also diminishes.
It is the Army's responsibility to provide upper-air data to support field artillery
as needed. These upper-air observations may be taken as frequently as every 2
hours, or only twice daily. Field artillery meteorological (ARTYMET) sections also
take valuable limited surface observations. Upper- air data primarily supports field
artillery operations, but other mission areas use it routinely. These surface and
upper- air meteorological messages should be quickly transmitted to WETMs. The
WETM combines the ATYMET data with other meteorological information to
support aviation, NBC, engineers, and other consumers.
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WEATHER FORECASTS
Weather forecasts are prepared by WETM forecasters and normally cover
periods from 1 hour out to 48. Outlooks extend from 3 days to 7 days. Several
factors determine the accuracy of the forecast. These factors include—
The length of time in advance that the forecast is required.
The area for which the forecast is made.
The quality and quantity of weather observations available to
the forecaster.
The quality and availability of communications.
The availability of USAF-provided weather data base.
Forecast accuracy normally diminishes as the forecast period increases. A
24-hour forecast is more accurate than a 72-hour outlook. Although extended
outlooks may not predict cloud base heights or exactly when the rain will start,
they can show expected movement of weather systems with associated cloud and
precipitation areas .
Forecasts and extended outlooks are the building blocks you use to determine
the effect of the weather on planning. The shorter time period and the greater the
number of observations in the forecast area, the higher the confidence you can
have in the accuracy of your analysis.
CLIMATOLOGY
Weather information required beyond the extended outlook (7 days) is based
upon historical climatological data. This information is important for long-range
planning, especially if you are to deploy to an unfamiliar AO. Climatology data
gives the commander average weather conditions and the weather extremes that
can be expected in the field. This assists in planning—
Future operations.
* Types of systems, equipment, and supplies.
• Personnel strengths.
You will need to work with your SWO while still in garrison to collect and
process climatology data.
SOURCES OF WEATHER SUPPORT
Weather support to Army tactical units is provided in two ways. The WETMs
provide all forecasts and supplemental weather information received from national
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and local sources, together with surface observations taken at each WETM
location. Some division WETM MOTs may be deployed forward (by direction of
the division commander) to supplement surface observations taken by Army
personnel. The Army is responsible for taking surface and upper-air observations
forward of the division command element and in direct support of Army weapon
systems and operations.
USAF TACTICAL WEATHER SUPPORT
FM 34-81/AFM 105-3 states Army doctrine and our requirement for weather
support. The USAF Directorate of Weather assigns weather forecasters and
observers, comprising WETMs, or special operations weather teams (SOWTs), to
tactical Army units to meet this need.
USAF forecasters are at the main CP at~
Echelons above corps (EAC).
Corps.
Divisions.
Separate brigades.
ACRs.
Division and corps aviation brigades.
Ranger regiments.
SFG headquarters and forward operating bases (FOBs).
Observers are assigned to the same locations listed above and assist
forecasters by taking surface weather observations. Limited observing functions
may exist at the SFGs, FOBs, and ranger regiments. MOTs may also be deployed
to selected tactical airfields and landing zones (LZs). Size and composition of
WETMs vary from as few as 4 observers and forecasters to teams with as many as
14 observers and forecasters plus 2 officers.
At EAC, corps, and division the senior weather officer is the tactical unit's
SWO. Although the SWO is a member of the special staff, he normally works with
the G2 and with the operations and plans sections. The SWO commands all the
WETMs at his tactical level and is under the operational control of the Army
commander.
Each SWO ensures that his WETM supports the commander's needs. For this
reason, it is important that you outline your specific requirements to your
supporting SWO. Weather support requirements must be validated (by the SWO
and the SIO) prior to deployment so that the WETM can make the necessary
2-8
FM 34-81-1
preparations. If new requirements surface in the field, or changes are required, you
notify your SWO. Give him enough lead time to allow for production changes.
ARMY WEATHER SUPPORT
By joint regulation, AR 1 15-10/ AFR 105-3, USAF responsibility for surface
weather observations ends at the division main CP. The Army's responsibility is to
take observations from the CP forward, and in direct support of Army weapons
systems anywhere in the AO.
As discussed earlier, the FALOP and ARTYMET data partially satisfy this
requirement. Weather satellite imagery will play a larger role as new systems are
designed to capture this data.
HOW G2 OR S2 RECEIVE WEATHER SUPPORT
It is your responsibility to provide weather and weather effects information to
your commander and supported or subordinate units. Methods may vary from unit
to unit and echelon to echelon. At higher echelons, the SWO has primary
responsibility for providing weather support. There, the G2 simply contacts the
SWO, states requirements, and receives the needed weather support.
If you have no SWO, you must pass the request up the chain of command to
a level where one is assigned. Once your requirements have been validated,
weather support products flow back over the same path. In addition to weather
forecast products, the SWO can provide specialized weather effects products. You
must provide the threshold values used in developing these products.
Figure 2-l| summarizes this flow. The SWO support to the brigade is shown
with an asterisk because only separate and aviation brigades have direct weather
support.
2-9
FM 34-81-1
RQMTS
RQMTS
PRODUCTS
PRODUCTS
CORPS
RQMTS
u
RQMTS
PRODUCTS
PRODUCTS
DIVISION
RQMTS
RQMTS
PRODUCTS
PRODUCTS
BRIGADE
RQMTS
O
RQMTS
PRODUCTS
PRODUCTS
BATTALION
RQMTS
PRODUCTS
COMPANY
iiSlBELOW:!::!:
swd
* SWO support will be found with the
separate brigade, ACR, combat aviation
brigade, ranger regiment, and special
forces group.
** Special forces battalions will have a
forcaster weather team at the FOB.
Figure 2-1. Weather requirements and production flow.
2-10
FM 34-81-1
TERRAIN ANALYSIS TEAM SUPPORT
Combat intelligence is composed of weather, enemy, and terrain; sometimes
called the WET trilogy. Below division, where a terrain team is not assigned, the
intelligence analyst working order of battle (OB) has the added responsibility for
terrain analysis. Your OB specialist relays the unit's requirements, through
channels, to the terrain team supporting the division. He also does whatever
limited local analysis is needed.
Once in the field, terrain and weather analyses in support of the intelligence
preparation of the battlefield (IPB) are based on locally updated terrain data bases
and the current weather forecast for the AO.
Terrain teams are responsible for analyzing the division geographic AI and
providing recommended courses of action based upon effects of weather under
current and forecast weather conditions. They produce graphical tactical decision
aids (TDAs) that help the commander and staff understand the effects of weather
on division operations. These IPB templates are available to you at either brigade
or battalion upon request.
The principal user of IPB templates is the divisional G2 staff, but terrain
teams will service needs of brigade and battalion S2s as priorities allow.
Separate brigades and other corps or EAC units obtain the same support via
the corps or theater G2. Lead time must allow production of tailored products, and
attached elements can expect to compete with other G2 and engineer priorities.
Many sta ndard products will already be available from the division's team.
See iTable 2-21 . The more you exercise terrain teams, the more responsive they will
be as they understand and learn to anticipate the needs of brigades and battalions.
In the field, new or updated terrain analysis products may be obtained
electronically or via courier.
USE OF INTELLIGENCE PREPARATION OF THE BATTLEFIELD TEMPLATES
IPB templates provide an integrated graphic portrayal of enemy doctrine and
the effects of weather and terrain in the AO and AI. Development of IPB products,
while still in garrison, based on climatology (provided locally by the WETM) gives
you a general idea of what average seasonal weather conditions will be in the AO.
2-11
FM 34-81-1
Table 2-2. Terrain analysis products.
• Observation, field of fire ^
> DZs and LZs
• Concealment and cover i
> Maneuver (mobility and
• Obstacles
trafficability)
• Cross-country nnovennent '
9 Key terrain
• LOG and MSRs i
► LOS, terrain perspectives
• Ground avenues of approach i
> Barriers and fortifications
• Air avenues of approach ^
> Weapon sites
• EW sites ^
> Surface drainage
• Beach, river ennbanknnent ^
> Soil analysis
studies
Once deployed, IPB products must be updated based on~
• Current weather observations.
• Periodic weather forecasts.
• Environmental effects products produced by the
terrain team.
By comparing the weather forecasts or current observations to the
climatology used in preparing the IPB templates, you can keep the commander
informed on trends.
Two examples illustrate how garrison-prepared IPB products can be updated
in the field. You have prepared IPB templates depicting mobility or counter-
mobility based on a climatic average of 2 inches of precipitation. Then the SWO
reports that the rates are higher than anticipated. You quickly modify the
templates and brief the commander.
2-12
FM 34-81-1
Then, if you have prepared air mobility corridor templates based on the
general low-level cloud ceilings (climatology) and high mountainous terrain, these
can be modified to determine the best and worst air corridors based on either
weather observations or forecasts.
You can obtain weather IPB overlays by asking for them from your higher G2.
The G2 will then task the SWO to produce the weather portion of the overlays.
Overlays may be used with either climatology for long-range planning or with
forecasts for a specific time. Combinations of several critical threshold values and
weather elements may be depicted on one overlay. This way a specific weapon
systems effectiveness can be briefed as a sum of the various weather elements
involved.
Remember that for long-range planning a climatology review and data
extraction is a time-consuming process. The more lead time you can give the G2
and the SWO, the mo re thorough the research and the higher quality of the
finished product. Use Appendixes B through J 0| as guid es to develop weather
overlays. The weather elements contained in [Table 2-3 1 may not address all of
your unit's weather needs. Other weather overlays that may be of interest are-
Atmospheric pressure and density altitude for
helicopters.
Areas where thermal sight target signatures will
be reduced.
Time periods when thermal crossover will occur.
Areas where heat and humidity will exceed mission
oriented protective posture (MOPP) 4 survivability
for time periods over 2 hours at hard work.
Long-range surveillance unit (LRSU) high altitude,
high opening (HAHO) infiltration corridors based on
upper- air weather conditions.
Weapon system performance capabilities based on
combined weather effects threshold values.
By combining climatology, terrain data, and the IPB process while still in
garrison, you get an idea of what to expect in the field. Then you use current
forecasts and local terrain data to update the weather and terrain analysis steps of
IPB.
2-13
FM 34-81-1
Table 2-3.
IPB weather overlay^
criteria.
WEATHER ELEMENTS
THRESHOLD VALUES
IMPACTED SYS 1 EMS
1.0 km
3.0 km
500 ft
1,000 ft
1,500 ft
5,000 ft
6 kn
13 kn
18 kn
30 kn
GT 32''C
LTO^'C
LT -lO^'C
Moderate
Freezing
DRAGON, Machine guns.
Main gun, TOW, CAS,
thermal viewers.
Nap-of-the-earth operations,
Airborne, helicopter target
acquisition.
CAS
COPPERHEAD engagements.
Visual reconnaissance, ADA
target acquisition.
Chemical.
Airborne - round parachute.
Military free fall -- ram air
parachutes, artillery smoke
loses its effectiveness,
artillary fire accuracy.
Helicopter maneuver.
Helicopter lift capabilities.
NVG (PVS-5).
Personnel survival.
Ground maneuver,
chemical, laser
systems, GSR.
Ground maneuver.
VISIBILITY
CLOUDS
SURFACE WIND
TEMPERATURE
WINDCHILL
PRECIPITATION
LEGEND: GT=
= Greater than
LT=: Less than
2-14
FM 34-81-1
CHAPTER 3
COMMANDER'S WEATHER INFORMATION REQUIREMENTS
Here we address the commander's weather requirements. And while the
unit's weather needs flow from the commander, it is your job to articulate and
convey these needs to the SWO. You do this either through your G2 or directly,
depending upon local custom.
But before you can be totally effective, you need to understand how the
SWO works and what kind of support he can provide. Plus, there are other factors
you must consider before asking the SWO for forecast support.
FORECASTS. OUTLOOKS. AND REPORTS
Every commander views his battlefield as having two distinct areas that can
be expressed in terms of distance and time. These are the AO and the AI. It is
impossible to be specific about distances here because different types of units will
travel at different speeds. And while distances may vary, time stays relatively
constant. Examples of time applied to both the AO and AI are shown in Table 3-1.
Table 3-1. Areas of operations and interest.
LEVEL OF COMA/IAND
TIME OF AO
TIME OF AI
BATTALION
Up to 3 hours
Up to 12 hours
BRIGADE
Up to 12 hours
Up to 24 hours
DiVlSION
Up to 24 hours
Up to 72 hours
CORPS
Up to 72 hours
Up to 96 hours
EAC
Up to 96 hours
More than 96
hours
The AO is an area of conflict necessary for military operations. It is a
geographical area assigned to a commander for which he has responsibility and in
which he has authority to conduct military operations. Commanders are assigned
an AO based on the mission, enemy, terrain, troops, and the time available
(METT-T).
3-1
FM 34-81-1
The action of the threat forces, the trafficability, and the weather conditions
in the AI are also of great concern to the commander. The AI includes the AO plus
adjacent friendly areas and areas occupied by threat forces that could jeopardize
the mission. The AI time span may be significantly increased over that of the AO
because of possible threat ground and air operations. Since the battlefield is fluid,
the land mass encom passing the AO and AI should be measured by the times
shown in iTable 3-11 . This is important because the SWO will satisfy your weather
support requirement by time sequencing weather forecasts for the geographical AO
and AI.
ESTABLISHING REQUIREMENTS FOR FORECASTING SUPPORT
Weather forecasts, like any other intelligence information, must be keyed to
those areas that encompass the commander's AO and AI planning horizons. The
geographic area covered by the forecast is directly related to the military
operations at each tactical level. For example: At battalion level, the
commander's concern revolves around how far his soldiers can travel or shoot in
12 hours. [Table 3-l| can be used to determine the geographic coverage required
for any forecast and each echelon by factoring in distance.
PERIODS OF FORECAST AND OUTLOOKS
While it is critical for the commander to have a weather forecast covering
current operations, it is not the only weather requirement he has. He must also be
aware of tomorrow's weather and how it may affect his unit's continuing
operations.
Therefore, instead of thinking only about current and forecasted weather for
the next 3 to 12 hours, his weather concern envelope may extend out several
days. This approach expands as you go up the tactical chain of command.
A n EAC com mander must be concerned with a 7- to 10-day weather
outlook. [Table 3-2| summarizes this concept. In every instance, the degree of
detail varies, and you must tell the SWO the forecast length required and, in turn,
put this information into the unit's tactical standing operating procedures (SOPs).
Generally, the commander needs detailed forecasts of selected weather
elements for the first 24 hours, in increments as short as 6 hours. Forecast
intervals beyond the first 24 hours are going to be longer.
3-2
FM 34-81-1
Table 3-2. Determining lengths of forecasts and outlooks.
LEVEL OF COMMAND
LENGTH OF
FORECAST/OUTLOOK
OF PRIMARY INTENT
LENGTH OF
FORECAST/OUTLOOK
FOR PLANNING
BATTALION
12 to 24 hours
48 hours
BRIGADE
24 hours
48 hours
DIVISION
24 to 36 hours
3 to 5 days
CORPS
1 to 3 days
5 to 7 days
EAC
2 to 4 days
7 to 10 days
FREQUENCY OF UPDATE
After deciding the geographic coverage and length of the forecast period,
you can then consider the frequency of forecast updates. Generally, an update
every 6 to 12 hours is sufficient for the first 24-hour period. Asking for forecast
updates more frequently than every 6 hours is counterproductive because the only
new data available would be unevaluated observations.
Forecasts extending beyond 24 hours should be revised daily. These
forecasts are based on hemispheric computer models that run every 12 to 18
hours. Table 3-3 summarizes the recommended frequency for weather forecast
updates.
Table 3-3. Update frequency.
LENGTH OF FORECAST/OUTLOOK
FREQUENCY OF UPDATE
to 12 hours
Every 6 hours
to 24 hours
Every 6 to 12 hours
24 to 72 hours
Every 24 hours
More than 72 hours
Every 24 to 72 hours
3-3
FM 34-81-1
SELECTING WEATHER ELEMENTS
Each weather forecast contains the standard weather elements observation
the battlef ield. You must identify those elements that are most important to you.
Table 3-4| identifies several common battlefield applications and those weather
elements that play a role in their operations.
Using a table like this, and discussions with your SWO, you can determine
the precise weather elements that are most important to your unit. Based on your
operation, systems, and personnel, there will be several weather effects threshold
values that you will want the SWO to be aware of. He records your needs as
standing requirements and will automatically report conditions that meet the
criteria.
For example: The height above ground level (AGL) of the base of clouds
that form a ceiling is important to the COPPERHEAD missile. If 600 meters is the
critical threshold value, you must tell the SWO so the WETM will spend extra time
trying to determine when, or if, that value will be reached.
Ousting surface winds over 35 knots are critical to air assault operations,
and parachutists require at least 1,000 feet of visibility AGL to visually see and aim
for a specific landing site within the drop zone (DZ). You must make sure the
SWO is informed of these values so he can concentrate his forecasting capabilities
on those thresholds that are critical to your unit.
CRITERIA FOR CHANGE
You have told the SWO when and how often you need a forecast. But what
happens if conditions change (weather forecasters change forecasts occasionally)?
What do you tell him about being notified? You will know, if you can answer this
question: What weather elements with specific thresholds are important to my
mission?
For example: In support of aviation your commander may specify that for
cloud ceilings under 500 feet he wants to receive a new updated forecast
whenever the ceiling changes (deteriorates or improves) by 100 feet from the
original forecast.
Since precipitation is important for ground maneuvers, a commander may
want to know when the forecast changes from no precipitation to rain or rain
showers.
3-4
FM 34-81-1
Table 3-4. Weather applications and criteria for
changes.
^\ WEATHER
\. EFFECTS
BAIILEFIELD ^s,,^
APPLICATION \.
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X
X
X
X
X
X
X
ARTILLERY FIRES
X
X
X
X
X
X
X
X
X
X
X
CONCEALMENT
X
X
X
X
X
X
X
X
X
CAMOUFLAGE
X
X
X
X
X
X
X
X
X
X
X
GROUND AVENUES OF APPROACH
X
X
X
X
X
X
X
X
AIR AVENUES OF APPROACH
X
X
X
X
X
X
X
X
X
X
X
X
CROSS-COUN 1 HY MOVEMENT
X
X
X
X
X
X
X
X
X
FORDING SITES
X
X
X
X
X
X
X
X
X
AIR DROP ZONES
X
X
X
X
X
X
X
X
X
X
X
HELIMOBILE LZ/PZ
X
X
X
X
X
X
X
X
X
X
X
X
LOG AND MSRs
X
X
X
X
X
X
X
X
NBC OPERATIONS
X
X
X
X
X
X
X
X
X
X
X
X
RADIO/RADAR
X
X
X
REMBASS EMPLACEMENT
X
X
X
X
X
X
INFILTRATION ROUTES
X
X
X
X
X
X
X
X
X
X
X
LEGEND: 0) Density altitude quality affects aircraft lift capability.
(2) For laser-guided weapons.
3-5
FM 34-81-1
SEVERE OR HAZARDOUS WEATHER
In addition to your continuous need for forecast updates for general weather
elements, you need non-forecasted or unanticipated severe or hazardous weather
warnings. These weather phenomena adversely impact your operational capability.
WETMs normally issue severe weather warnings and advisories. Check for the
values at which each weather element becomes known as severe. Severe weather
conditions are listed below. (As a working aid you might add the exact critical
valu es for your unit's operations, systems, and personnel in place of the X in [Table
3-4[ ) When forecast (and especially when not forecasted), you will be concerned
with such conditions as—
• Tornadoes.
• Thunderstorms producing winds in excess of 45 knots and hail greater
than 3/4 of an inch.
• Hurricanes and typhoons.
• Precipitation (rain or snow) when X inches fall in Y hours.
• Surface winds in excess of X knots.
• Maximum and minimum temperatures; when a forecast value misses the
actual temperature by X degrees.
You want to know that an earlier forecast for light snow was amended to a
forecast of a 16 inch accumulation within the next 12 hours. We cannot over
emphasize that you need to work with your next higher headquarters S2 or G2 and
the SWO so that your needs are realistically stated and can be supported. All of
your weather support needs should be reviewed every 6 months in garrison and as
required in the field.
LIGHT DATA
Another weather-related element that your commander needs is light data.
The introduction of NVD and night vision goggles (NVG) have made many night
operations feasible. Your SWO provides official times for sunrise and sunset,
beginning and ending of civil twilight (BMCT and EECT), beginning and ending of
nautical twilight (BMNT and EENT), length of absolute darkness, moonrise,
moonset, lunar phase in percent, and time periods for using NVD and NVG. Light
data to support NVD is needed because there are times when there is not enough
moon or star light to use them.
Civil twilight is sufficient for conduct of combat operations while nautical
twilight permits most ground movements without difficulty. Nautical twilight
allows a general visibility of up to 400 meters (1 ,320 ft) and lets you distinguish
silhouettes from the background.
3-6
FM 34-81-1
The actual duration of light varies considerably with latitude and time of
year. For example, in the vicinity of 35 to 40 degrees north latitude, civil twilight
generally occurs 30 to 45 minutes before sunrise and after sunset. In the tropics,
twilight is much shorter.
Once light requirements are determined, relay them to your next higher SIO
and SWO. This information is important for your commander because he needs to
know not only when he can begin friendly military operations (day or night), but
also when threat operations could begin.
OTHER CONSIDERATIONS
Although high frequency (HF) radio wave propagation forecasts are not
normally available to the SWO, he can make arrangements before he deploys to
receive these forecasts. When available, they should be given to every signal and
intelligence organization. The signal officer should know that when HF is not
effective, it may be because of solar activity rather than enemy jamming.
The USAF Global Weather Central can routinely provide solar forecast
products to the SWO even in the field. Other data, such as tidal information and
sea state conditions, can be obtained from the SWO but are normally only provided
to specific Army units, and then upon special request.
RECEIPT OF FORECASTS
Every tactical echelon should receive the weather forecast prepared and
briefed to the commander at the next higher echelon. With no SWO at a maneuver
brigade, you receive both the forecast briefed at division covering the division AO
and the forecast made by the division SWO specifically for your brigade. Each
forecast message received should be worked by you to discover the direct weather
impacts on your unit.
A commander wants the weather forecast. He also needs the effects and
impacts of the forecasted weather interpreted for his specific operations, systems,
and personnel. iTable 3-5] provides a matrix of the kind of data and weather
forecasts that Army units might need. Remember to schedule your forecasts so
they arrive in time for you to prepare your commander's briefing.
3-7
FM 34-81-1
Table 3-5
. Typical support requirements.
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X
X
X
X
X
X
X
X
X
X
X
X
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(0 to 48 HOURS)
EXTENDED FORECAST
X
X
X
X
X
X
X
X
X
X
X
(3 to 7 DAYS)
AVIATION FORECAST
X
X
X
X
X
X
X
X
X
X
LIGHT DATA
X
X
X
X
X
X
X
X
X
X
X
SEA STA lb DATA
X
X
X
LOW-LEVEL WINDS
X
X
X
X
X
X
X
X
X
UPPER-LEVEL WINDS
X
X
X
X
X
X
X
X
X
DEEP ATTACK
X
X
X
X
X
WEATHER
PRECIPITATION
FORECAST
X
X
X
X
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X
X
X
X
X
X
SEVERE WEATHER
X
X
X
X
X
X
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X
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X
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HF PROPAGATION
X
X
X
X
X
E-0 DATA
X
X
X
X
X
X
INVERSIONS
X
X
X
VISIBILITY
X
X
X
■
X
X
X
X
X
3-8
FM 34-81-1
CHAPTER 4
WEATHER TACTICAL DECISION AIDS
As your commander's weather interpreter, you are familiar with weather and
its effects on operations, systems, and personnel. History provides many
examples where weather, properly taken into consideration, contributed to the
successful accomplishment of the mission. Conversely, when weather has not
been properly considered, the consequences have been disastrous. To gain the
maximum benefit from the data provided here, you must know the weather effects
critical threshold values for the operations, systems, and personnel in your unit.
Specific BFA-associated WTDAs located in the appendixes will be helpful.
EXPLANATION AND PRESENTATION
Conduct of the battle within the AG is influenced by the effects of weather.
You advise and alert the commander on how, when, where, and why the
battlefield dynamics will change because of weather. The key is to learn to exploit
opportunities offered by weather while reducing or minimizing the adverse effects.
The geographical layout of the battlefield is important to you because the
times and distances across the AG and AI vary with the size, type of unit, and
mission. These constraints affect the type of weather forecasts needed in terms
of time and area. The duration of the forecast must meet or exceed the planning
and execution cycles.
The following are some operations affected by critical weather extremes.
Poor visibility degrades target acquisition and engagement, C\
troop and vehicle mobility, maneuver options, and air operations.
High and low winds affect chemical weapons and smoke employment,
air operations, antenna setup and employment, personnel (windchill),
target tracking devices, and accuracy of artillery fire support systems.
Temperature extremes impact troop safety and performance,
trafficability, maintenance, aircraft limits, optical systems,
employment of chemical weapons and smoke, and accuracy of fire
support systems.
4-1
FM 34-81-1
Precipitation degrades mobility, trafficability, nuclear and
chemical weapons, smoke, the effective use of laser-guided
munitions, maneuver options, air operations, target acquisition,
and tactical ballistic missile (TBM) employment and launching.
Cloud cover affects all types of air operations. Cloud cover also
can limit or enhance the effects of nuclear weapons, smart
weapons, and smoke.
Severe weather conditions (such as blizzards, hailstorms,
thunderstorms, strong winds, and freezing rain) impact almost
every battlefield operation.
Even the best weather information or intelligence will not necessarily be the
decisive factor in winning the battle. However, it can be a force multiplier when
applied during planning. It will almost certainly affect the degree of success you
have. Weather may not be the sole determining factor as to the GO, NO-GO
decision, but it will surely influence a commander's decision on how best to use
combat power.
SOURCE OF WEATHER VALUES
Most of the critical weather values used here are a compilation of validated
values taken from a variety of military publications including system technical
manuals, other FMs, and proponent requirements. Some subjective values (based
on personal experience and usually not validated) are also included. You will
probably find that you will add values of your own based on practice and
experience. (These insights, forwarded to the proponent office, will be valuable in
updating the contents of future iterations of this manual.)
USE OF THE APPENDIXES
Time is in short supply in the field and, in some cases, higher priority tasks
will perm it you very litt le time to develop weather information for the commander's
briefings. Appendixes B through [n have been developed to help you quickly
identify critical weather values and their effects on the operations, systems, and
personnel of the unit. These WTDAs allow you to swiftly turn weather forecasts
and observations into meaningful weather effects information. Practicing this skill
in garrison will be a great help in the field.
4-2
FM 34-81-1
CONTENTS OF APPENDIXES
Appendix A contains a step-by-step guide through the process of translating
adverse weather conditions into force impacts. In addition, it features quick
references tables to identify critical value ranges of five basic weather elements.
For each weather element, the critical value ranges are shown impacting Army
BFAs, E-O, and threat systems. The five elements evaluated are cloud ceilings,
reduced visibility, surface wind, temperature, and precipitation. These references
apply to critical values shown in Appendixes B through [N
Appendix 0| contains a current list of weather and environmental elements or
parameters identified by BFA proponents and other Army agencies. The impacts of
some of these are not fully known and data may not presently be collected.
Appendix P| contains useful conversion factors. An expanded list of weather
terminology is presented in the glossary.
Weather data and impacts reflected in these appendixes are predicated on
normal unit configuration.
THE WEATHER BRIEFING
This section contains an example that will help you visualize how the WTDA
charts and tables can be used to develop and present a comprehensive weather
and weather effects briefing. For this exercise you are the 82 of a battalion task
force (TF) located in North Korea in January. Your TF consists of two companies
of M-1 tanks and two companies of Mechanized Infantry equipped with the M-2
infantry fighting vehicle (IFV). The TF has a fire support team from a direct
support 155-mm self-propelled artillery battalion. The TF is conducting defensive
operations as part of a brigade operating in the main battle area. You have just
received th e weather forecast from brigade headquarters as illustrated in
Figure 4-1
4-3
FM 34-81-1
FROM: BRIGADE
TO: BATTALION
SUBJECT: WEATHER FORECAST
LOCATION: PUNGSAN AREA - 40,49N 128.09E (OR USE UTM GRID)
VALID PERIOD: 121200Z TO 131200Z JAN 92
Clear skies, surface winds northerly at 10 knots gusting
to 20 knots, visibility will be unlimited except occasionally
1 to 2 miles in blowing snow. Low temperatures
expected to dip to between -20 and -25 degrees F,
warming to a high near degrees F.
OUTLOOK: 131200Z TO 151200Z:
Increasing cloudiness, chance of heavy snow and
temperatures warming to near 10 degrees F.
LIGHT DATA: BMNT 122147Z, BMCT 1 22221 Z, SR 1 22251 Z,
SS 130820Z, EECT 130851Z, EENT 130925Z,
MR 1924Z, MS 081 9Z
NIGHT VISION GOGGLE USE PERIOD: 0149Z TO 0532Z
NOTE: Because blowing snow conditions are produced as a result of the combination of strong
winds with loose snow on the ground, "blowing snow" is not listed as a separate weather
condition in this manual. However, you need to be aware that such conditions will seriously
degrade visibility. Similar conditions occur with blowing sand and blowing dust.
Figure 4-1. Example of a weather forecast.
Based on this forecast, you quickly scan the tables in | Appendix A| . You find
that forecasted temperatures may have a critical impact o n several TF sy stems.
Turning to the Armor and Mechanized Infantry sections of Appendixes C and|j,
you identify actual syste ms that are ini pacted by the latest weather forecast. In
addition, you also review Appendixes F and [l] and identify any additional impacts
on E-O systems and personnel.
4-4
FM 34-81-1
You alert your commander and the staff about the adverse impact of the
forecasted weather. You prepare two simple charts to be used during your
commander's stand-up briefing. You may want to leave these charts posted in the
CP throughout the day for continued reference.
Remember to update the charts when a new forecast is issued by the WETM.
Methods used in briefing your commander during the morning and evening
briefings may vary greatly from command to command. The formats illustrated
should be used as a guide and, of course, modified to suit your particular situation.
The first chart presented to your commande r is a stand ardized chart containing
the important elements of the weather forecast. [Figure 4-2| illustrates how the
weather elements and parameters contained in the forecast might be displayed on
the board. Blown up to poster size and covered with acetate, this chart can be
updated easily.
Figure 4-3| shows color codes as one way to display potential weather impacts
on operations, systems, and personnel in your unit.
Another way would be to write the words ''moderate" and ''severe" in those
blocks affected. Do not list all the equipment or systems, but have the list
available to answer questions posed by the commander or staff. Stress those
critical systems during the verbal portion of your briefing.
If the weather c onditions ch ange significantly during the period covered by the
SWO's forecast (see [Figure 4-l[ ), then an updated impact chart will have to be
prepared. Because a brigade or battalion's AI is small, the SWO's forecast is likely
to be uniform across the AI.
4-5
FM 34-81-1
WEATHER FORECAST
VALID FOR 121200Z to 131200Z
LOCATION: PUNGSAN
24-HOUR FORECAST:
SKIES: CLEAR MORNING AND NIGHT, PARTLY CLOUDY IN
THE AFTERNOON, BASES 3,000 FEET.
VISIBILITY: UNLIMITED, OCCASIONALLY 1 TO 2 MILES IN
BLOWING SNOW DURING AFTERNOON.
WINDS: NORTH TO NORTH WEST, 10 TO 15 KNOTS,
OCCASIONAL GUSTS TO 25 KNOTS IN AFTERNOON.
TEMPERATURES: MAX: 10°F MIN: -20°F
72-HOUR OUTLOOK:
CLOUDY SKIES, SNOW FLURRIES DURING AFTERNOON
HOURS LOWERING VISIBILITY TO 2 TO 4 MILES.
TEMPERATURES: MAX: 20°F MIN: -5°F
MOONRISE: 1924Z
MOONSET: 081 9Z
NIGHT VISION
GOGGLE USE:
0149Z TO 0532Z
LIGHT DATA
BMNT:
1247Z
BMCT:
2221Z
SUNRISE:
2251Z
SUNSET:
0820Z
EECT:
0851Z
EENT:
0925Z
Figure 4-2. Example of a weather forecast chart.
4-6
FM 34-81-1
WEATHER IMPACT CHART
PERIOD 121200Zto 131200Z
IMPACTED
ITEMS
NBC DEFENSE
NIGHT VISION
DEVICES
CLOUDS
GREEN
GREEN
PRECIPI-
TATION
GREEN
GREEN
WIND
GREEN
VISIBILITY
TEMPER-
ATURE
CSS
GREEN
TOW/DRAGON
GREEN
M-1/M-2
GREEN
SMOKE/
CHEMICAL
GREEN
GROUND RADAR
GREEN
GREEN
PERSONNEL
GREEN
GREEN
THREAT
GREEN
GREEN
GREEN
NO IMPACT
MODERATE IMPACT
(Normal effectiveness reduced 25 to 75%.)
SEVERE IMPACT
(Normal effectiveness reduced to 0to25%).
GREEN
Figure 4-3. Example of a weather impacts display chart.
4-7
FM 34-81-1
APPENDIX A
HOW TO USE THE TABLES
AND TYPE UNIT REFERENCE TABLES
This appendix explains how to use the in dividual BFA appendixes
Appendix A is your starting point. [Figures A-l| through |A-5| provide a quick look at
potential weather conditions that might impact on your unit. Forecasts specify
cloud bases, visibility, surface winds, temperature, and precipitation.
If forecasted values exceed the thresholds shown in the figures, you have a
weather impact. You then take a closer look at Appendixes B through [N
to
determine which unit-specific operations, systems, and personnel are involved.
Step 1. Using the latest weather forecast received from the WETM, or a
current observation from your AO, note the numeric values listed for cloud bases,
visibility, surface w inds (inclu ding gusts), high and low temperatures, and
precipitation. (See [Table 2-l| for relationship between precipitation intensity and
accumulation.)
Step 2. Go to [Figures A-l| to [ A-5[ . These display the five weather
conditions reported in the forecast. For example, suppose vi sibility is forecast to be
3,000 meters (or 1.9 statute miles). Referring to [Figure A-l| , look for the
horizontal dotted line representing 3,000 meters. You see that it intersects solid
vertical lines for special operations, mechanized infantry, lEW, light infantry,
aviation, artillery, armor, and air defense.
If you serve in one of these type units, you have a weather, impact. To see
just exactly what kind and how severe the impact is, you look in the appendix
devoted to that type of unit.
Note that in some figures, the solid vertical lines extend both up from the
bottom and down from the top of the graph. This means there are two ranges of
impact for the same weather element. As an example, temperatures can be too
hot or too cold.
Step 3. Using the data in Figures A-1
to
A-5. check the functional areas
affected by the forecast or observation. Look to see which, if any, are involved in
current or near-term operations during the time of the forecast. A quick look
A-1
FM 34-81-1
planning guide can be prepared (similar to I Table 2-3 ) that will help you in preparing
your weather briefings, charts, and IPB analysis.
Remember, these tables consider the effects of only five of the most
common weather elements on units (except Special Forces). There are other
weather elements and parameters that affect Army operations, systems, and
personnel. As their critical val ues and impac ts are qualified, they will be added to
future iterations of this manual. Appendix O lists a variety of these elements and
parameters together with the functional area affected.
A-2
FM 34-81-1
AIR DEFENSE
ARMOR
ARTILLERY
UGHT INFANTRY
MECHANIZED INFANTRY
SPECIAL OPERATIONS
THREAT
Figure A-1. Weather effects from reduced visibility.
A-3
FM 34-81-1
CO
10
CO
CM
UJ
o
o
o
o
lO
Cvj
o
Si
lO
5>
o
in
AIR DEFENSE
ARMOR
ARTILLERY
AVIATION
E-0
ENGINEER
UGHT INFANTRY
JEW
MECHANIZED INFANTRY
NBC
PERSONNEL
SPECIAL OPERATIONS
THREAT
o
o
o
o
o
o
in
o
o
o
8
CO
o
o
o
cvT
8
O
Figure A-2. Weather effects from clouds.
A-4
FM 34-81-1
CO
1^
in
CO
T—
00
(O
■^
CM
C\J
CVJ
OJ
1- CD
in
CO
c\i
AIR DEFENSE
ARMOR
ARTILLERY
AVIATION
E-0
ENGINEER
LIGHT INFANTRY
lEW
MECHANIZED INFANTRY
NBC
PERSONNEL
SPECIAL OPERATIONS
THREAT
Figure A-3. Weather effects from surface winds.
A- 5
FM 34-81-1
D
CO
Lu
O
CO
H
UJ
X
z
LU
cr
z
<
S
CV!
s
CVJ
CO
CO
AIR DEFENSE
LIGHT INFANTRY
MECHANIZED INFANTRY
PERSONNEL
SPECIAL OPERATIONS
THREAT
S
S
§
8
O
CM
Figure A-4. Weather effects from temperature.
A-6
FM 34-81-1
CO
CO
5g
I
I
i
LU
Q
O
I-
X
o
LU
Q
AIR DEFENSE
LIGHT INFANTRY
MECHANIZED INFANTRY
PERSONNEL
SPECIAL OPERATIONS
THREAT
Figure A-5. Weather effects from precipitation.
A-7
FM 34-81-1
APPENDIX B
WEATHER EFFECTS ON
AIR DEFENSE ARTILLERY
Air defense artillery (ADA) requires weather information for both deployment
and employment. Deployment requires climatological data, trafficability, and
severe weather forecasts. Weather conditions affecting employment vary
according to the type of weapon system used. When missle systems require radar
surveillance, elements such as refractive index and precipitation must be known.
Other systems require visual target acquisition. Listed below are weather effects
for ADA that are not contained in the WTDA tables.
CLOUDS AND SKY COVER. Overcast skies degrade visual acquisition and tracking.
Low overcast limits the effectiveness of aerial illumination devices. Clouds limit the use of
NVD by blocking natural light from the moon and stars.
HUMIDITY. Moisture in the air affects the refractive index and may degrade radar
effectiveness.
ILLUMINATION. Most NVD require about a quarter (23 percent) of the moon, 30
degrees above the horizon, scattered clouds, and the sun more than 5 degrees below the
horizon. Detailed products dealing with the use of E-0 devices are available from the SWO.
PRECIPITATION. Rain, sleet, or snow prevents visual target acquisition and tracking.
Precipitation attenuates radar signals and degrades or prevents infrared homing.
REFRACTIVE INDEX. This index (see glossary for a description) degrades target
acquisition and tracking radar.
SURFACE WIND. Strong surface winds produce blowing dust, sand, or snow and may
cause computers to malfunction.
TEMPERATURE. High temperatures can degrade the effectiveness of electronic
systems, and very low temperature may affect mechanical devices. Extreme cold produces
detectable ice-fog exhaust trails from certain weapon systems and vehicles.
THUNDERSTORMS AND LIGHTNING. Intense electrical storms will probably mean
that electronic systems will be out of service.
VISIBILITY. Low visibility decreases the effectiveness of visual collection systems.
B-1
FM 34-81-1
Table B-1. Weather effects from cloud celling.
WEATHER
VALUE
(FEET)
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT [ REMARKS
SYSTEM/EVENT ! REMARKS
LT 500
Weapon selection i Type
j weapon
LT 1,000
Army aviation operations 1 See app E
LT 2,500
Visual detection/ i
identify aircraft 1
LT 5,000
Visual detection, i
identify aircraft [
B-2
FM 34-81-1
Table B-2. Weather effects from reduced visibility.
WEATHER
VALUE
(METERS)
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT | REMARKS
SYSTEM ^EVENT | REMARKS
LT200
NVG (PVS-5) 1
LT400
NVS IPVS-2) ]
LT600
NVS (PVS-4) 1
LT 1,200
NVS (TVS-2, TVS-5) ]
LT 2,000
NVS (TVS-4) j
LT 3,000
VULCAN !
CHAPARRAL I
LT 5,000
STINGER !
REDEYE j
B-3
FM 34-81-1
Table B-3. Weather effects from surface wind.
WEATHER
VALUE
(KNOTS)
SEVERE DEGRADATION
SYSTEM/EVENT
REMARKS
MODERATE DEGRADATION
SYSTEM /EVENT
REMARKS
GT7
GT20
GT25
GT35
GT40
GT50
GT66
GSR
GSR
Increased
noise
Communications
antennas
NOE operations
Personnel
HAWK acquisition
radar
HAWK support system
Illumination radar
(MPQ-57)
Personnel
Communications
antennas
HAWK launcher
Increased
noise
B-4
FM 34-81-1
Table B-4. Weather effects from temperature.
WEATHER
VALUE
(»F/''C)
LT -25/-32
LT -20/-28
LT-0/-18
LT 32/0
GT 85/29
SEVERE DEGRADATION
SYSTEM /EVENT
REMARKS
HAWK missile system
Dry cell battery
Personnel
I Only 20%
1 effective
I
I
GT 90/32
GT 95/35
GT 120/49
GT 125/52
HAWK missile system
Personnel
I See |app L
! for water
consumption
REDEYE
STINGER
Generators
MODERATE DEGRADATION
SYSTEM/EVENT
Generators
Maintenance
Wheeled vehicles
Dry cell battery
20-mm ADA gun
Personnel
Personnel
Dry cell battery
REMARKS
I wo Arctic
j kit
I
I
I
Takes five
times
longer
wo winter
kit
Only 40%
effective
Uses cold
precaution
app L
See
for
windchill
I See |app L
I for water
[ consumption
I Will not
! hold
I charge
B-5
FM 34-81-1
Table B-5. Weather effects from precipitation.
WEATHER
CONDITION
SEVERE DEGRADATION
SYSTEM^EVENT
REMARKS
MODERATE DEGRADATION
SYSTEM/EVENT
REMARKS
Light rain
or snow
Moderate
rain or
snow
Wheeled vehicles
Mortar operations
Wheeled vehicles
Sight glass
fogs up
LOS communications
Personnel movement
Laser systems
Target acquisition
Equipment storage
Heavy
rain or
snow
Mortar operations
Personnel movement
LOS communications
Target acquisition
Laser systems
Thunder-
storm/
lightning
HAWK (within 1.2
miles)
Ammunition
Radar system (within
1.2 miles)
Refueling operations
Communications
Equipment storage
Safety
Interference
Light
freezing
rain
Personnel
Wheeled vehicles
Moderate
freezing
rain
Personnel
Wheeled vehicles
Missile launching
SNOW
DEPTH
(INCHES)
GT3
Personnel movement
GT6
GT 12
GT 20
GT30
Personnel movement
Wheeled vehicles
Tracked vehicles
Wheeled vehicles
Tracked vehicles
B-6
FM 34-81-1
APPENDIX C
WEATHER EFFECTS ON
ARMOR
Armor operations are influenced primarily by those weather elements that
degrade trafficability and visibility. Although the effect may be more pronounced
for armor operations, weather elements have generally similar types of impacts on
other units. Listed below are weather effects for armor that are not contained in
the WTDA tables.
BAROMETRIC PRESSURE. The weight of the air affects gunnery computations and
ballistic performance.
CLOUDS AND SKY COVER. Low overcast clouds limit the effectiveness of aerial
illumination devices. Overcast clouds tend to limit heating of inactive targets and lower
target detection ranges for thermal sights. NVD are limited by clouds blocking natural hght
from the moon and stars. Close air support (CAS) and aerial resupply missions are
degraded by low clouds.
HUMIDITY. Coupled with high temperatures, high humidity decreases crew effectiveness
in closed vehicles.
ILLUMINATION. Best use of most NVD requires about a quarter (23 percent) of the
moon, 30 degrees above the horizon, scattered clouds, and the sun more than 5 degrees
below the horizon. Detailed products dealing with the use of E-0 devices are available from
the SWO.
PRECIPITATION. Rain and snow degrade trafficability and limit visibility. They also
degrade target acquisition and NVD.
SURFACE WIND. Trajectory projections and first round hit capability affected by high
crosswinds.
STATE-OF-THE-GROUND. Frozen ground improves mobility and significantly increases
the time available to prepare fighting positions. Deep snow slows movement of tracked
vehicles. Frozen ground and mud affects munitions, sensors, and indirect fire.
TEMPERATURE. Temperatures influence the type of lubricants to be used, engine
warm-up periods, and sustained rates of fire for weapons. High temperatures decrease the
time personnel can remain in vehicles. High temperatures cause gun tube droop.
C-1
FM 34-81-1
shimmering, mirages, and vehicle exteriors to be too hot to touch. Extremely high
temperatures increase water consumption. Low temperatures degrade the baUistics of main
guns and require frequent starting of engines and may increase maintenance problems and
possible detection by the enemy. Extremely low temperatures reduce personnel
effectiveness and decrease the availability of water because of freezing. Temperatures
changing from above to below freezing can freeze stationary tracks into the mud.
VISIBILITY. Visibility affects visual acquisition, degrades laser range finding and target
acquisition systems.
WINDCHILL. Winds affect the apparent temperature in which soldiers must operate.
The windchill table must be consulted to determine the actual effective temperature.
C-2
FM 34-81-1
Table C-1. Weather effects from cloud ceilings.
WEATHER
VALUE
(FEET)
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT | REMARKS
SYSTEM/EVENT ,' REMARKS
LT300
CAS ] See app E|
LT 1,000
Army aviation 1 Seelapp E|
C-3
FM 34-81-1
Table C-2. Weather effects from reduced visibility.
WEATHER
VALUE
IMETERS)
SEVERE DEGRADATION
SYSTEM /EVENT
REMARKS
MODERATE DEGRADATION
SYSTEM/EVENT
REMARKS
LT 100
Forward Observer (FO)
M-1 Tank
Speed
LT 200
LAW
NVG (PVS-5)
Infrared aiming light
(PAQ-4)
LT400
NVS (PVS-2)
LT500
DRAGON
FO
LT 600
NVS (PVS-4)
LT 800
Tracked vehicle (day
operation}
LT 1,000
TOW
DRAGON
DRAGON thermal sight
{TAS-5)
106-mm recoilless rifle
M-60 machine gun
7.62-mm coaxial
machine gun
LT 1,200
NVS (TVS-2 and TVS-5)
LT 1,600
CAS
I See app E
60-mm mortar (non-HE
round)
Tracked vehicle (day
operation)
.50-cal machine gun
LT 2,000
NVS (TVS-4)
LT 3,200
CAS
M-60 main gun
25-mm chain gun
M-1 main gun
TOW thermal sight
(UAS-12)
Handheld thermal
viewer (PAS-7)
Thermal night observing
device (UAS-11)
60-mm mortar (HE
round)
See app E
LT 4,500
107-mm mortar
C-4
FM 34-81-1
Table 0-3. Weather effects from surface wind.
WEATHER
VALUE
{KNOTS)
SEVERE DEGRADATION |
MODERATE DEGRADATION |
SYSTEM/EVENT
REMARKS
SYSTEM/EVENT
1 REMARKS 1
LT25
1 1
Incendiaries | |
GT7
1
1
1
GSR
1 Increased
! noise
GT 10
Chemical emplacement
1 Less
j effective
GT 13
Airborne DZ limit
! Less
1 effective
GT 15
Acoustic sensors
! Less
! effective
GT 15
Cross-
winds
TOW, DRAGON
I Impacts
! tracking/
1 reduces
j range
GT20
GSR
Increased
noise
Communication [
antennas i
NOE operations 1
GT25
Personnel I
GT30
Helicopter operations
May cancel
mission
1
1
1
1
1
See app E|
GT40
Personnel
Radar (PPS-5)
Antenna
breaks
1
4
GT45
Acoustic sensors
Less
[ effective
1
1
■
GT50
Connnnunications
antennas
1
1
1
I
1
1
1
1
_i
1
1
1
1
1
1
1
C-5
FM 34-81-1
Table C-4. Weather effects from temperature.
WEATHER
VALUE
CF/'C)
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT \ REMARKS
SYSTEM/EVENT [ REMARKS
LT -25/-32
TOW !
DRAGON 1
Handheld thermal 1
viewer (PAS-7) I
Dry cell battery ! Only 20%
! effective
Personnel |
Generators j wo Arctic
1 kit
M-1 Tank i wo winter
kit
CFV, M3 1 wo winter
1 kit
Laser infrared | wo
observation set j external
(GVS-5) j power
LT -20/-28
NVS (PVS-4 and TVS-5) j wo low
j temp
1 adapter
Maintenance ! Five times
1 longer
Tanks, M-1, M-60 ! Accuracv
LT0/-18
Wheeled vehicles » wo winter
! kit
Dry cell battery j Only 40%
j effective
LT 20/-6
Thermal night observing | wo Arctic
device (UAS-1 1) j kit
I wo
Platoon early warning ! BA3090
system (TRS-2) I battery
! wo low
DRAGON j temp
i adapter
LT 32/0
NVG (PVS-5) I wo Arctic
1 kit
Small arms and machine i Functions
guns ! affected
Personnel | See |app L
! for
j windchill
GT 85/29
Dry cell battery 1 Will not
! hold
j charge
Personnel * See|app L|
GT 125/52
All NVS i Operations
1 deteriorate
Generators j Operations
j deteriorate
Laser infrared i Operations
observation j deteriorate
set (GVS-5) 1
WP rounds [ Special care
! for storage
C-6
FM 34-81-1
Table C-5. Weather effects from precipitation.
WEATHER
CONDITION
Light
rain or
snow
Moderate
rain or
snow
Heavy
rain or
snow
Thunder-
stornn/
lightning
Light
freezing
rain
Moderate
freezing
rain
SNOW
DEPTH
(INCHES)
GT3
GT6
GT 12
GT20
GT30
SEVERE DEGRADATION
SYSTEM /EVENT
Wheeled vehicles
Personnel movement
LOS communications
Target acquisition
Personnel
Wheeled vehicles
Personnel movement
Wheeled vehicles
Tracked vehicles
REMARKS
MODERATE DEGRADATION
SYSTEM/EVENT
REMARKS
M-1 Laser range finder [ Fake
Wheeled vehicles
ranging
returns
LOS communications
Personnel movement
Target acquisition
GSR
Equipment storage
-h
Ammunition storage
Refueling
Communications
Equipment storage
j Safety
I Interference
Personnel
Wheeled vehicles
Personnel movement
20-mm and 40-mm
ammunition
Wheeled vehicles
Tracked vehicles
C-7
FM 34-81-1
APPENDIX D
WEATHER EFFECTS ON
ARTILLERY
Artillery in the field is heavily weather dependent. Not only must you
contend with those weather effects common to all other units but you must also
compensate for a number of special effects in the area of target acquisition and
aiming. Listed below are weather effects for artillery operations that are not
contained in the WTDA tables.
BAROMETRIC PRESSURE. Air pressure affects projectile trajectory, barofuzing, and
fire control calculations.
CLOUDS AND SKY COVER. Low ceilings affect target acquisition systems and
terminally guided munitions. Low overcast clouds will limit the effectiveness of aerial
illumination devices.
DENSITY. The thickness of the atmosphere (heavy air) affects fire control. The greater
(heavier) the density, the shorter the range.
HUMIDITY PROFILE. This scale is used to compute virtual temperatures for baUistic
firing data.
ILLUMINATION. The best use of most NVD require about a quarter (23 percent) of the
moon, 30 degrees above the horizon, scattered clouds, and the sun more than 5 degrees
below the horizon. Additional weather products dealing with the use of E-0 devices are
available from your SWO.
PRESSURE PROFILE. Barometric pressure profiles are essential in both baroarming and
barofuzing. They are required for calculating densities for baUistic firing data.
REFRACTIVE INDEX. This index affects radar, laser, and infrared distance
measurements.
SURFACE WINDS. Trajectory data and first round hit capability are degraded by high
crosswinds. Winds affect the accuracy of rocket fire and Firefinder radar trajectory
computations.
SURFACE TEMPERATURE. Frozen ground increases the time a crew has to stabilize
their weapon. Extreme cold affects gun accuracy and fuse functioning. High temperature
D-1
FM 34-81-1
affects stability of ammunition such as white phosphorus (WP). It also reduces rate of fire
greatly because of crew heat fatigue.
TEMPERATURE PROFILE. This is another condition that affects calculations of baUistic
artillery firing. The profile is used to compute virtual temperatures for artillery firing.
Extreme cold affects gun accuracy and fuse functioning.
THUNDERSTORMS AND LIGHTNING. Electrical storms restrict the use of some
munitions and fuse types.
VISIBILITY. This affects visual target acquisition, fire adjustment, and E-0 target
designation. Reduced visibility affects the placement of forward observers (EG) and fire
support teams.
WINDS ALOFT. Strong winds aloft impact all baUistic projectile aiming calculations.
Accurate and timely meteorological data can compensate for the problem.
WIND PROFILE. Wind profiles play a major role in baUistic wind compensations for
artillery firing.
D-2
FM 34-81-1
Table D-1 . Weather effects from cloud ceilings.
WEATHER
VALUE
(FEET)
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT | REMARKS
SYSTEM/EVENT j REMARKS
LT500
ATACMS 1 Target
1 acquisition
LT600
COPPERHEAD ! Target
j acquisition
LT800
SADARM 1 Target
j acquisition
LT 1,000
ATACMS j Target
i acquisition
Army aircraft ! See app E
LT 1,500
COPPERHEAD ! Target
1 acauisition
LT 3.300
SADARM I Target
1 acquisition
D-3
FM 34-81-1
Table D-2. Weather effects from reduced visibility.
WEATHER
VALUE
(METERS)
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT ! REMARKS
SYSTEM/EVENT \ REMARKS
LT200
FO 1
NVG IPVS-5) !
Infrared aiming light !
(PAQ-4) j
LT400
NVS (PVS-2) j
LT 500
DRAGON :
FO j
LT600
NVS (PVS-4) j
LT 1 ,000
TOW 1
DRAGON thermal sight I
(TAS-5) j
LT 1,200
NVS (TVS-2, TVS-5) j
LT 2,000
NVS (TVS-4) j
LT 3,000
TOW thermal sight j
(UAS-12)
Handheld thermal i
viewer {PAS-7) !
Thermal night observing !
device {UAS-11) j
LT 3,500
AFO !
D-4
FM 34-81-1
Table D-3. Weather effects from surface wind.
WEATHER
VALUE
(KNOTS)
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT | REMARKS
SYSTEM/EVENT ! REMARKS
GT7
GSR ! Increased
j noise
GT20
GSR I Increased
I noise
Communications i Setting up
antennas 1
GT25
Personnel j
GT30
Meteorological processor ] Inhibits
(GMD-1) ' balloon
1 launch
Meteorological data j
system (TMQ-31) i
Meteorological 1
measuring set 1
(TMQ-38) j
GT35
Artillery (detection radar 1 Stow
(TPQ-36) j antenna
155-mm how !
GT40
Personnel ]
GT50
Communications t Setting
antennas 1 up
D-5
FM 34-81-1
Table D-4. Weather effects from temperature.
WEATHER
VALUE l°F/°C)
SEVERE DEGRADATION
1 MODERATE DEGRADATION |
SYSTEM/EVENT
! REMARKS
SYSTEM/EVENT
t REMARKS
LT -25/~32
TOW
DRAGON
Rocket launcher
(M202A1)
Handheld thermal
viewer (PAS-7)
Dry cell battery
Personnel
i Only 20%
I effective
Generators
] wo arctic
1 kit
LT -20/-28
NVS (PVS-4)
Maintenance
j wo low
1 temp
! adapter
I 5 times
[ longer
LT 0/-18
Wheeled vehicles
Dry cell battery
t wo
! winter kit
! Only 40%
j effective
LT 20/-6
Thermal night
observation device
(UAS-11)
Platoon early warning
system (TRS-2)
DRAGON
j wo
1 arctic kit
! wo
! BA3090
1 battery
1 Need low
i temp
[ adapter
LT 32/0
NVG (PVS-5)
Personnel
Small arms and
machine guns
] wo
j arctic kit
[ See app L|
1 Tor wind-
! chill
1 Effective-
1 ness
j reduced
GT 85/29
Personnel
] beelapp u
1 for temp/
1 humidity
1 index
GT 95/35
Personnel
Dry cell battery
1 Will not
1 hold
1 charge
j See lapp L|
! for water
1 consumption
1
i
1
1
D-6
FM 34-81-1
Table D^. Weather effects from temperature (continued).
WEATHER
VALUE
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT ! REMARKS
SYSTEM /EVENT j REMARKS
GT 125/52
All NVS i
Generators j
155-mm how (Ml 98) ■
ammunition
105-mm how !
TACFiRE 1
Laser infrared |
observation !
set (GVS-5) 1
LANCE I
WP artiliery rounds j Become
j unstable
D-7
FM 34-81-1
Table D-5. Weather effects from precipitation.
WEATHER
CONDITION
SEVERE DEGRADATION
SYSTEM /EVENT
i REMARKS
MODERATE DEGRADATION
SYSTEM/EVENT
REMARKS
Light rain
or snow
Mortar operations
Wheeled vehicles
Sight glass
fogs up
Moderate
rain or
snow
Wheeled vehicles
LOS communications
Personnel movement
Target acquisition
Platoon warning system
(TRS-2)
GSR
Acoustic systems
Equipment storage
Laser systems
Heavy
rain or
snow
Mortar operations
Personnel movement
Laser systems
LOS communications
Target acquisition
H
j Safety
I Interference
Thunder-
storm/
lightning
Ammunition
Refueling
Communications
Equipment storage
4-
Light
freezing
ram
Personnel
Wheeled vehicles
Moderate
freezing
rain
Personnel
Wheeled vehicles
SNOW
DEPTH
(INCHES)
GT3
Personnel movement
GT6
Personnel movement
20-mm and
40-mm ammunition
Wheeled vehicles
GT 12
Wheeled vehicles
GT20
Tracked vehicles
GT30
Tracked vehicles
D-8
FM 34-81-1
APPENDIX E
WEATHER EFFECTS ON
AVIATION
Army aviation operates over the length and breadth of the battlefield.
Missions are varied and include both fixed-wing and rotary-wing aircraft.
Battlefield aviation assets play a role in a host of missions including mobility,
countermobility, survivability, C\ fire support, maneuver, air defense, lEW, combat
service, and combat service support. Weather support is critical and impacts both
planning and execution.
Aviation planners must include weather conditions in takeoff areas,
employment routes, engagement zones, PZs, and LZs to list just a few. Aviation
commanders must consider all weather conditions both favorable and unfavorable.
Accurate forecasts in the AO and AI are more critical to air operations than most
land operations. This is especially true for the deep battle missions.
Listed below are weather effects for aviation that are not contained in the
WTDA tables.
CLOUDS AND SKY COVER. Clouds are always a major consideration for aviation
operations. Low overcast clouds will limit the effectiveness of aerial illumination devices.
Overcasts tend to limit heating of inactive targets and lower target detection range for
thermal sights. NVD are limited by clouds blocking natural illumination from the moon or
the stars. CAS and aerial resupply missions are degraded by low clouds.
DENSITY ALTITUDE. This is a critical measurement that determines if an aircraft has
enough lift capabilities and performance to get off the ground. Too much density altitude
limits fuel, weapons, and passenger loads.
DEWPOINT. The dewpoint (see the | glossary] for an explanation) serves as a warning of
possible fog formation or icing conditions. It is a key measurement in computing density
altitude (see above).
ICING. Ice on lifting surfaces affects the aerodynamics of the aircraft. Even a little ice is
a big problem.
E-1
FM 34-81-1
ILLUMINATION. NVD are most efficient with about a quarter (23 percent) of the moon,
30 degrees above the horizon, scattered clouds, and the sun more than 5 degrees below
the horizon. Detailed products dealing with the use of E-0 devices are available from the
SWO.
INFRARED CROSSOVER. This is a temperature condition that affects target
acquisition. Your SWO will tell you when this is expected to occur.
PRECIPITATION. Rain and snow affect visibility and the safety of both crew and
airframe. In some instances, precipitation may cause predetonation of munitions.
PRESSURE ALTITUDE. This computed figure affects all aircraft engine performance.
SNOW DEPTH. Snow compounds ground handling problems. Light, powdery snow may
interfere with helicopter hover operations.
STATE-OF-THE-GROUND. Ground conditions impact on the effectiveness of serially
dehvered munitions.
SURFACE WINDS. Strong winds, especially cross-winds, affect aircraft control near the
ground during take-off and landings. They also affect ground speed for low-level frights.
TEMPERATURE. High temperatures reduce lift capability. Cold temperatures increase
maintenance requirements and the time needed to accomplish each task. The number of
personnel that can be carried on a flight is reduced due to the weight of cold-weather gear.
THUNDERSTORMS AND LIGHTNING. Extreme weather that includes thunderstorms
and hghtning is very hazardous to inflight operations, refueling, and rearming operations.
TURBULENCE. Severe weather and clear air turbulence is a critical condition affecting
all aviation assets and missions. It may cause aircraft structural damage or even crashes
during take-offs and landings. Severe turbulence may cancel all operations.
VISIBILITY. The lack of good visibility affects landings and take-offs, visual
reconnaissance, target acquisition, E-0 target designation, terminally guided munitions, and
the ability to distribute scatterable mines.
WINDS ALOFT. Winds at flight altitudes always affects navigation and fuel
consumption.
E-2
FM 34-81-1
Table E-1. Weather effects from cloud ceilings.
WEATHER
VALUE
(FEET)
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT ! REMARKS
SYSTEM /EVENT \ REMARKS
LT300
NOE 1
Day target acquisition, 1
flat terrain 1
Day, flat terrain ! AR 95-1
IT 500
Night target acquisition, |
flat terrain i
Day target acquisition, j
mountain terrain j
NOE day, mountain ! AR 95-1
terrain !
Night flat terrain [
j AR 95-1
LT 1,000
Night target acquisition |
mountain terrain i
Military free-fall HAHO 1 Minimum
! base of
1 cloud over
j DZ
Army aviation, aerial j
observations i
CAS j
LT 1,100
HELLFIRE ! Low angle
j approach
LT 2,600
HELLFIRE 1 High angle
1 approach
E-3
FM 34-81-1
Table E-2. Weather effects from reduced visibility.
WEATHER
VALUE
IMETERS)
LT 200
LT400
LT600
LT 800
LT 1,000
LT 1.200
LT 1,600
LT 2,000
SEVERE DEGRADATION
SYSTEM /EVENT
REMARKS
NVG (PVS-5)
NOE operations
NVS (PVS-2)
NVS (PVS-4)
Target acquisition
TOW
NVS (TVS-2. TVS-5)
LT 2,500
LT 3,200
LT 3,800
KIOWA (OH-58)
I Target
! acquisition
Military free-fall HAHO
H
1 Mininnunn
1 altitude for
! RAP
MODERATE DEGRADATION
SYSTEM/EVENT
i REMARKS
LAW
Infrared aiming light
(PAQ-4)
Helicopter, day, flat or
nnountain
NOE
I AR 95-1
DRAGON
DRAGON thermal sight
(TAS-5)
M-60 machine gun
-+-
Helicopter, night, flat or ] AR 95-1
mountain i
.50-cal machine gun !
Aerial target acquisition ]
Night vision sight i
(TVS-4)
+
TOW
TOW thermal sight
(UAS-12)
Handheld thermal
viewer (PAS-7)
Thermal night
observation device
(UAS-11)
Fixed wing, nighty flat
terrain operations,
target acquisition
7.62-mm coaxial aerial
machine gun
E-4
FM 34-81-1
Table E-3. Weather effects from surface wind.
WEATHER
VALUE
(METERS)
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT \ REMARKS
SYSTEM/EVENT \ REMARKS
GT 15
1
Acoustic sensors i Less
j effective
GT 15
Cross-
wind
component
MOHAWK (0V/RV-1D) | Grounded,
1 max for
! takeoff
! or landing
TOW j impacts
! tracking
GT 15
Gust
spread
Two-bladed helicopter i
GT20
Communications [
antennas j
NOE operations i
Forward area refueling !
point !
Two-bladed helicopter j
GT25
COBRA {AH-D rocket | 2.75 inch
launcher i rockets
1 degraded
Personnel I
GT25
Cross-
wind
component
UTE {U-21) 1 Grounded,
HUR0N(C-12) ! max for
I takeoff or
I landing
GT30
Two-bladed helicopter !
COBRA (AH-I) !
CHINOOK (CH-47) !
IROQUOIS IUH-1) !
Four-bladed helicopter |
GT40
COBRA (AH-1S) 1
CAYUSE (OH-6) !
SEMINOLE (U-8) !
Personnel j
GT45
Acoustic sensors j Less
j effective
Four-bladed helicopter i
KIOWA (OH-58) !
BLACKHAWK (UH-60) I
APACHE {AH-64) j
GT 50
Communications i
antennas !
SKY CRANE (CH-54) j
GT60
MOHAWK (OV/RV-ID) 1
HURON (C-121 1
UTE (U-21) 1
E-5
FM 34-81-1
Table E-4. Weather effects from temperature.
WEATHER
VALUE
(°F/°C)
SEVERE DEGRADATION
SYSTEM /EVENT
REMARKS
MODERATE DEGRADATION
SYSTEM /EVENT
I REMARKS
LT -29/-34
BLACKHAWK (UH-60)
Ice fog will
limit/halt
visual flight
I
I
-I-
I
I
I Only 20%
1 effective
I
BLACKHAWK (UH-
60)
wo
special
service
LT -25/-32
TOW
Dry cell battery
Personnel
Generators
wo arctic
kit
LT -20/-28
NVS (PVS-4 and
TVS-5)
Maintenance
wo low
adapter
Takes five
times
longer
LT0/-18
Wheeled vehicles
Dry cell battery
j wo winter
I kit
! Only 40%
j effective
LT 32/0
NVG (PVS-51
Personnel
! wo arctic
kit
1 See lapp L
ndchi ■
wir
GT 85/29
Personnel
See lapp L
tennp,
hunnidity
index
GT 90/32
MOHAWK (0V/RV-1D),
IROQUOIS (UH-1)
I Above 4,000
! ft
UTE (U-21),
MOHAWK
(0V/RV-1D),
HURON (C-12),
IROQUOIS (UH-1>,
BLACKHAWK
(UH-60)
! Lift
GT 95/35
Personnel
See |app L]
for water
consumption
Dry cell battery
COBRA (AH-I)
Wilt not
hold
charge
Lift/flight
time
GT 119/49
HURON (C-12)
At sea level
GT 125/52
All NVS
Generators
E-6
FM 34-81-1
Table E-5. Weather effects from precipitation.
WEATHER
CONDmON
SEVERE DEGRADATION
SYSTEM/EVENT
REMARKS
MODERATE DEGRADATION
SYSTEM/EVENT
REMARKS
Light rain
or snow
Wheeled vehicles
Moderate
rain or
snow
Wheeled vehicles
LOS communications
Personnel movement
Target acquisition
Equipment storage
Laser systems
+
Heavy
rain
or snow
Artillery detection radar
(TPQ-36)
Personnel movement
LOS communications
Target acquisition
Laser systems
Rocket firing
SLAR
Radar systems
I Predetonate
Thunder-
storm/
lightning
MOHAWK (0V/RV-1D)
Imbedded
thunder-
storms
Ammunition
Aircraft
Refueling
Communications
Equipment storage
SLAR
AR 95-1
I Safety
! Interference
I
I
Light
freezing
ram
Aircraft {wo deice)
AR 95-1
Personnel
Wheeled vehicles
-4-
Moderate
freezing
rain, ice
Personnel
Wheeled vehicles
I AR 95-1
Rocket firing
Aircraft {with deice)
Predetonate
AR 95-1
Heavy
freezing
rain, ice
Aircraft (with deice)
AR 95-1
SNOW
DEPTH
(INCHES)
GT3
Personnel movement i
All fixed-wing aircraft !
GT6
Personnel movement
All fixed-wing aircraft
Propeller
clearance,
braking
20-mm and 40-mm
ammunition
Wheeled vehicles
GT 12
Wheeled vehicles
GT 20
Tracked vehicles
GT30
Tracked vehicles
E-7
FM 34-81-1
APPENDIX F
WEATHER EFFECTS ON ELECTRO-OPTICAL SYSTEMS
Army battlefield capabilities have improved significantly in recent years due,
in part, to the development and deployment of E-0 systems. A great variety of
these systems are in the Army's inventory and more are being programmed.
Basically, E-O systems enhance the Army's battlefield reconnaissance, target
acquisition, and target destruction capabilities.
They enable ground and aviation units to see better and accurately strike the
enemy day or night even during limiting weather conditions. Since the weather
parameters affecting E-O devices are numerous and the use of E-O systems is so
widespread, they deserve special attention as a separate category of tactical
systems.
CLASSIFICATION OF ELECTRO-OPTICAL SYSTEMS
E-O systems are classified as active (overt) or passive (covert). Active
systems emit a detectable wavelength signal, while a passive system senses
emitted or radiated energy. E-O systems include image intensifiers, infrared
imagers, laser designators, and low-level-light (LLL) television (TV). To fully
understand how weather impacts these systems, we need to know their basic
operating principles.
NVG are an example of passive image intensifiers. They use extremely LLL
sources (starlight), and amplify that light so that objectives are visible. These
systems operate in the visual and near-infrared wavelengths.
LLL TV is a passive system and is capable of picking up targets at light
levels below those usable to the human eye. This TV electronically enhances the
video signal and makes it visible to the operator. Night sights, heat seeker
munitions, and infrared detector munitions are examples of passive infrared
imaging systems.
These systems are characterized as near infrared (short wavelength) or far
infrared (long wavelength). For infrared imagers to function properly, there must
be a temperature or thermal contrast between target and background area
F-1
FM 34-81-1
(signature). They can tell the difference between target "hot spots" and the rest
of the target itself, like a warm engine in a cold truck.
Laser designators are active systems. They are used with smart munitions
capable of receiving reflected laser light. The designator "pings" a target with a
laser beam at a specified wavelength. The receiver in the munitions recognizes the
reflected beam and homes in on the designated target. These designators do not
emit light in the visible spectrum and, therefore, cannot be easily seen or detected.
When combined with E-O guided munitions, the transmitted laser beam
reflecting off the target greatly enhances the delivery accuracy over conventional
delivery techniques. However, the E-O guided munitions must receive the reflected
beam in time to make course changes prior to hitting the target. If the beam is not
reflected off the target or transmitted, or reception is disrupted, a miss will
probably result.
Figure F-l| illustrates the portion of the light spectrum used by the different
categories of systems employed by the Army.
F-2
FM 34-81-1
Z
INFRARED
VISIBLE
NEAR
MID
.38
.73
2.5
5.0 3.0
OPTICAL DEVICES
Day s^ht
Day iefevision
Bktachrome ff/m
HEAT SEEKERS
REDEYE
STfNGER
MISSILES
TOW
DRAGON
THERMAL DEVICE
AA//PAS-7 Handhe/d fffermai viewer
ACTIVE INFRARED
Armed vehicte periscopes
SHJLLELAGH opticai fink
IMAGE INTENSIFIERS
/nd/vidt/a/ weapon night sight
NVG
NVO
Crew-served weapon night sight
Night vision viewer
THERMAL DEVICES
TOW night sight
DRAGON night s^ht
Tank thermai sight
NVD /ong range
LASER DESIGNATORS
COPPERHEAD
HELLFIRE
IJVSER RANGEFINDERS
MtSOAJ Rangeh'nders
.38
.F8
2.5
5.0 S.O
MICRONS
f'4.0
Figure F-1. Microwave ranges of selected Army E-0 systems.
FM 34-81-1
ENVIRONMENTAL IMPACT
The performance of E-0 systems depends on three basic factors:
• E-0 characteristics of the target and its background on the battlefield.
• The atmosphere between the E-0 system and the target and its background.
• The sensitivity of the E-0 detector system (to include human operator
performance).
Weather conditions affect the first two factors, both directly and indirectly
and are summarized in Table F-1. The most fundamental environmental conditions
inhibiting E-O signals are~
• Attenuation or reduction of the signal by atmospheric moisture such as clouds,
precipitation, fog, and high humidity.
• Temperature affecting atmospheric refraction near the surface.
• Temperature contrast between the surrounding environment and the target.
• Winds kicking up dust and sand.
LLL.
Table F-1. Weather effects on E-0 devices.
SEVERE DEGRADATION
MODERATE DEGRADATION
ENVIRONMENTAL
PARAMETERS
VISIBLE
INFRARED
VISIBLE
INFRARED
NEAR
MID
FAR
NEAR
MID
FAR
CLOUDS
ALL TYPES
FOG
X
X
X
X
X
X
X
X
X
PRECIPITATION
LIGHT TO MODERATE RAIN OR SNOW
HEAVY RAIN OR SNOW
X
X
X
X
X
X
X
X
AEROSOLS (SMOKE, DUST. SAND)
MODERATE DENSITY
HEAVY DENSITY
X
X
X
X
X
X
X
X
WATER VAPOR
HIGH HUMIDITY
(GT 80 PERCENT AND NEAR
A SOURCE OF WATER)
X
X
X
In addition to TV and binoculars, visible light systems include the TOW day
sight and image intensifiers such as the individual-served weapon sight and the
tank gunner's periscope. Systems that use available light are the easiest to defeat
with obscurants such as haze, smoke, dust, and precipitation because visible light
F-4
FM 34-81-1
has a short wavelength and can be more easily attenuated.
As the wavelength of the light spectrum used by an E-O system increases,
the less it is affected by obscurants. However, the long wavelength E-O system
provides less target resolution. Near infrared systems like the handheld thermal
viewer can penetrate some light fog oil and diesel oil smokes. Far-infrared
systems, such as thermal sights for the Apache helicopter. Ml tank, TOW, and
DRAGON, use longer wavelengths of the spectrum and can penetrate low densities
of WP smoke and other obscurants that defeat both visible and near infrared.
In addition to attenuation from an obscurant, E-O devices are also affected by
atmospheric refraction. Basically, the sun's heating of the surface air creates
sufficient vertical motion or turbulence to cause this effect. A mirage is caused by
this heating and can make a building appear to move or even cause a target to
disappear altogether. Such apparent displacements can lead to target misses.
Although these refractive conditions are associated with periods of high heat,
this condition has been observed over a snow cover when the air temperature was
25 degrees below zero Fahrenheit. The higher you are from the surface, the less
likely you will encounter mirages.
Other parameters that impact on many E-O systems are weather conditions
affecting the level of illumination. Although the level of light affects all devices
operating in the visible spectrum, image intensifiers are influenced the most. Too
much or too little light adversely affects the use of NVD.
On relatively clear nights with a near full moon, you can normally operate
without the aid of NVD. With less than a full moon, there may still be too much
light.
Too much light, when amplified by NVD, saturates the viewing area as seen
through the device and makes the device unusable because light and dark
contrasts are no longer possible. When illumination is limited, NVG must be used.
For partial or heavy overcast skies with little moonlight, even these light levels may
be too low to use NVG.
Additionally, terrain influences on available illumination must be considered.
Even though illumination may be adequate to support the use of NVD, flying in a
valley with shaded areas may end disastrously.
F-5
FM 34-81-1
CLOUDS
"Smart" weapons such as COPPERHEAD and the air-launched HELLFIRE have
critical cloud ceiling values. If these weapons pass into a cloud, they will lose
"lock on" and miss their laser-designated target. Another system affected by low
clouds is SADARM. Using E-O detectors, SADARM searches in a circular pattern
at a fixed angle. As these munitions descend, the area they see becomes smaller.
Low cloud ceilings drastically reduce their target search areas and time.
THERMAL CONTRAST
Millimeter wave and infrared E-0 devices require a temperature difference
between the target and its background. Bad weather can limit system
performance. As the contrast diminishes, a condition is reached where the target
is no longer discernible from the background and target acquisition becomes a
problem.
Thermal imagers produce images of targets in scenes, somewhat similar to
those seen on ordinary TV. The major difference is that, instead of observing light
(visible energy) in the scene, thermal imagers observe heat (infrared energy)
emitted, reflected, or generated by the objects in the scene.
The amount of infrared energy is determined principally by the object's
temperature, its surface reflectivity, and its structural properties. Natural infrared
energy is produced when objects absorb sunlight. Winds can change the image
contrast by making target and background closer to the same temperature.
Man-made energy, particularly in vehicles, results from the heat of fuel
combustion and the friction of moving parts. Infrared energy is not as greatly
diminished at night as is visible energy. Thermal imagers tend to function as well
or better during nighttime than during the day. For this reason, they are often used
as night sights.
A target may be acquired with a thermal imager only if the amount of infrared
energy of the target is sufficiently different from that of the background. This
difference, called thermal contrast, is the difference between the temperatures of
the target and its background.
Wind, rain, snow, humidity, and clouds reduce the temperature contrast
between target and its background and even cause thermal reversal where instead
of a "hot" target against a "cold" background, you find a cold target against a hot
F-6
FM 34-81-1
background. This can occur in the early morning and late afternoon when a
thermal sight encounters a condition where some inactive targets without an
internal heat source will warm up or cool off to the same temperature as the
background.
In this instance, thermal devices will not be able to see targets because the
difference in temperature is not enough to be detected. The sensitivity of the
thermal device to the difference in temperature and the rate at which a target is
heating or cooling will determine how long this "thermal crossover" will occur.
Most metal targets heat up or cool off faster than the ground and vegetation
in the background. At night a metal target appears to be colder than the
background, but with the sun shining on it, the target appears to be hot compared
to the relative coolness of a background of trees or bushes.
In bright sunshine, the thermal crossover period may be just a few seconds.
On cloudy days, however, the thermal crossover period may be a number of
minutes. When this happens, optical sightings must then replace the infrared
devices. Listed below are weather elements effecting thermal contrast at
crossover time.
CLOUDS. Clouds will reduce the thermal contrast. Lower and thicker clouds have a
stronger influence than higher or thinner clouds.
SURFACE WIND. Wind causes the temperatures of both the target and background to
become closer to the air temperature, and as a result, closer to each other.
HUMIDITY. Moist air does not enhance the rate of cooling as much as dry air. With high
humidity and a moist background, the thermal contrast would be minimal between target
and background. If the air was dry, the coohng influence on the moist background would
cause a greater thermal contrast.
PRECIPITATION. FaUing rain and snow have cooling effects that bring target and
background temperatures closer together. In the case of operating vehicles, the
temperature contrast may be increased since the precipitation will have little effect on the
heat generated in the engine compartment and the exhaust.
The relationship between weather effects and E-O systems is very complex
since the result is a function of the precipitation particle size and the wavelength of
the E-O system.
F-7
FM 34-81-1
ELECTRO-OPTICAL SUPPORT PRODUCTS
You obtain E-O support from the SWO. These products identify periods of
time during which NVG can be effectively used. In addition to E-O, your SWO has
other predictive products that you might need. Check with him for a hst.
F-8
FM 34-81-1
APPENDIX G
WEATHER EFFECTS ON
ENGINEERS
Engineer operations are influenced by past, current and future weather
conditions. The interaction of weather with terrain produces a greater impact on
engineer operations than previously understood. A source of help in identifying
weather and terrain impacts is the terrain analyst team at division. Below are some
weather effects on engineer operations that are not contained in the WTDA tables.
CLOUDS AND SKY COVER. Low clouds can limit the effectiveness of aerial illumination
devices.
FREEZE AND THAW DEPTH. The frost line impacts site selection, construction,
excavation, and trafficability.
HUMIDITY. Extreme humidities affect handhng, storage, and use of building materials. When
coupled with high temperatures, humidity affects personnel and significantly increases the time
to perform physical work.
ILLUMINATION. Optimum use of most NVD requires about a quarter (23 percent) of the
moon, 30 degre es above the horizon, scattered clouds, and the sun more than 15 degrees below
the horizon. See | Appendix F| for further information on E-0 devices.
PRECIPITATION. High rainfall rates influence river currents, water depth, and bridging
operations. It comphcates other construction or maintenance jobs, affects flooding, river-
crossings, soil bearing strength, and explosives.
SNOW DEPTH. Snow affects site selection, construction, and flood prediction.
STATE-OF-THE-GROUND. Ground conditions impact mining operations, trenching, and
any excavation job. Snow cover can impact the emplacement of scatterable mines.
SURFACE WINDS. Ground level winds affect river crossings, port management, and all
watercraft. Construction projects in chronic wind areas may need to recalculate structural
strength figures.
G-1
FM 23-81-1
TEMPERATURE. High temperatures impact trafficability, influence flood control, and dictate
the use of certain construction materials. Cold weather influences ice thickness and river
crossings, Ice flow problems affect bridges. For example, armored vehicle launched bridges
(AVLBs) are affected by warming if they were set up on frozen ground. Alternating freezing
and thawing (frost heaves) may destroy the effectiveness of emplaced mines.
THUNDERSTORM AND LIGHTNING. Electrical storms, and the associated rain and wind,
affect electronic systems in general and antennas, shelters, and mobility in particular.
SEA STATE. This condition affects site selection and the operations of port and beach
facilities.
G-2
FM 34-81-1
Table G-1. Weather effects from cloud ceiling.
WEATHER
VALUE
(FEET)
SEVERE DEGRADATION
MODERATE DEGRADATION 1
SYSTEM/EVENT I REMARKS
SYSTEM/EVENT I REMARKS |
LT 1 ,000
— 1
Army aviation I See
app E
1
G-3
FM 23-81-1
Table G-2. Weather effects from reduced visibility.
WEATHER
VALUE
{METERS)
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT I REMARKS
SYSTEM/EVENT ! REMARKS
LT 150
River crossings i Reduced
I speed
G-4
FM 34-81-1
Table G-3. Weather effects from surface winds.
WEATHER
VALUE
(KNOTS)
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT \ REMARKS
SYSTEM/EVENT [ REMARKS
GT7
GSR ! Increased
j noise
GT20
GSR 1 Increased
j noise
Communications j
antennas ^
River crossings Reduced
speed
Crane operations 1 Increases
I fuel con-
sumption,
1 reduces
lift
GT25
Personnel I
GT30
Crane operations I Terminates
GT35
Medium girder bridge I
Float bridging I Waves
GT40
Personnel !
GT50
Communications i
antennas [
G-5
FM 23-81-1
Table G-4. Weather effects from temperature.
WEATHER
VALUE
l°F/»C)
SEVERE DEGRADATION
SYSTEM/EVENT
REMARKS
MODERATE DEGRADATION
SYSTEM/EVENT
REMARKS
LT -25/-32
Dry cell battery
Personnel
j Only 20%
I effective
Generators
Mine detectors
wo Arctic
kit
wo Arctic
kit, short
battery
iife
LT -20/-28
Maintenance
I Takes five
! times
I longer
LT0/-18
Wheeled vehicles
Dry celt battery
Military explosives
wo winter
kit
Only 40%
effective
LT 32/0
Personnel
See lapp T]
for wind-
chill
GT 85/29
Personnel
See lapp Ll
for temp/
humidity
index
GT 95/35
Personnel
I See |app L
! for water
i consumption
Dry cell battery
I Won't hold
1 charge
GT 125/52
Generator-type
blasting
machines
Demolition kits
Mine detectors
Generators
I
G-6
FM 34-81-1
Table G-5- Weather effects from precipitation.
WEATHER
CONDITIOiM
SEVERE DEGRADATION
SYSTEM/EVENT
REMARKS
MODERATE DEGRADATION
SYSTEM/EVENT
REMARKS
Light rain
or snow
Mortar operations
Wheeled vehicles
Target acquisition
j Sight glass
I fogs
I
I
Moderate
rain or
snow
Heavy rain
or snow
Thunder-
storm/
lightning
Light
freezing
rain
Moderate
freezing
rain
Mortar operations
Mines (snow)
Personnel movement
LOS communications
Target acquisition
Construction/bridging
j Sight glass
I fogs up
Personnel
Wheeled vehicles
LOS communications
Personnel movement
Ground emplaced mines
scattering system
Target acquisition
Equipment storage
Wheeled vehicles
Mines
Ammunition
Aircraft
Refueling
Communications
Equipment storage
Personnel
Wheeled vehicles
! Rain
Safety
I Interference
SNOW
DEPTH
(INCHES)
GT3
GT6
GT 12
GT20
GT30
Personnel movement
Mines
Wheeled vehicles
Tracked vehicles
Personnel movement
Mines
20-mm and 40-mm
ammunition
Wheeled vehicles
Tracked vehicles
G-7
FM 34-81-1
APPENDIX H
WEATHER EFFECTS ON
LIGHT INFANTRY
Infantry operations are influenced primarily by those weather elements that
degrade trafficability and visibility. The effect may be significant for infantry
operations, but weather elements have similar impacts on other units. The
following contains other weather effects that are not contained in the WTDA
tables.
CLOUDS AND SKY COVER. Low overcast clouds limit the effectiveness of aerial
illumination devices. Overcast clouds limit heating of inactive targets and lower target
detection range for thermal sights. NVD are hmited by clouds blocking natural moonlight
or starlight. CAS and aerial resupply missions are hampered by low clouds.
HUMIDITY. When coupled with high temperatures, humidity decreases the effectiveness
of crews in closed vehicles.
ILLUMINATION. The use of most NVDs requires about a quarter (23 percent) of the
moon, 30 degrees abo ye the horizo n, scattered clouds, and the sun more than 5 degrees
below the horizon. Se q Appendix F| for weather products dealing with E-O devices.
PRECIPITATION. Rain and snow degrade trafficability, limit visibility, and affect certain
target acquisition and NVD.
STATE-OF-THE-GROUND. Ground state affects trafficability and movement rates.
Frozen ground improves mobility and will increase the time available for preparing fighting
positions.
SURFACE WIND. Trajectory data and first round hit capability are degraded by high
crosswinds.
TEMPERATURE. High and low temperatures influence the type of lubricants used,
engine warm-up periods, and sustained rates of fire for weapons. High temperatures
decrease the time soldiers can remain in vehicles and increase water consumption. Low
temperatures degrade the ballistics of main guns, require frequent starting of engines,
increase maintenance problems, and increase possible detection by the enemy. Extreme
low temperatures reduce personnel effectiveness, and decrease availability of water due to
freezing.
H-1
FM 34-81-1
VISIBILITY. Poor visibility affects visual sighting, laser range finding, and E-0 target
acquisition systems. Poor visibility increases the survivability of infantry units.
WINDCHILL. See Appendix L for a discussion on windchill
H-2
FM 34-81-1
Table H-1. Weather effects from cloud ceilings.
WEATHER
VALUE
(FEET)
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT ! REMARKS
SYSTEM/EVENT ! REMARKS
LT300
CAS j See app E
LT 500
CAS ] See|app E|
LT 1 ,000
High altitude parachute I
operations j
'
Army aviation ! See app E
H-3
FM 34-81-1
Table H-2. Weather effects from reduced visibility.
WEATHER
VALUE
(METERS)
SEVERE DEGRADATION
MODERATE DEGRADATION
1
SYSTEM/EVENT ! REMARKS
1
SYSTEM/EVENT I REMARKS
LT200
1
1
LAW 1
NVG (PvS-5) I
infrarsd aiming light
(PAQ-4)
LT400
\
NVS (PVS-2) 1
LT500
DRAGON 1
Fo ;
LT600
1
NVS (PVS-4) !
LT 1,000
TOW 1
i
I
r
DRAGON i
DRAGON thermal sight s
(TAS-5) !
106-mm recoiiless rifle !
M-60 machine gun I
LT 1,200
1
NVS (TVS-2 and TVS-5) !
LT 1 ,600
1
60-mm mortar (non-HE i
round) 1
.50-cal machine gun 1
CAS j See app E
1
1
LT 2,000
1
1
i
NVS (TVS-4) !
LT 3,200
I
1
1
1
i
1
1
i
1
1
1
I
TOW thermal sight |
(UAS-12) 1
Handheld thermal j
viewer (PAS-7) j
Thermal night i
observation !
device (UAS-11) !
CAS ! See app E
bO-mm mortar (Hb ,
round)
LT 4,500
1
1
81 -mm mortar I
LT 5,000
1
1
120-mm mortar 1
1
1
1
I
1
1
\
I
1
i
1
H-4
FM 34-81-1
Table H-3. Weather effects from surface wind.
WEATHER
VALUE
(KNOTS)
SEVERE DEGRADATION
SYSTEM /EVENT
REMARKS
MODERATE DEGRADATION
SYSTEM/EVENT
REMARKS
LT 25
Incendiaries
GT7
GSR
Increased
noise
GT 10
Chemical emplacement
Less
effective
GT13
Airborne DZ limit
Lass
effective
GT 15
Acoustic sensors
Less
effective
GT 15
cross-
wind
TOW
Impacts
tracking
GT18
RAP
4-
GT20
GSR
I Increased
I noise
Communications
antennas
NOE
GT25
4-
Personnel
See app L
GT30
Helicopters
i may cancel
I mis sion
I See [app E
GT40
Personnel
I See|app L
GT45
Acoustic sensors
I Less
I effective
GT 50 Communications
antennas
H-5
FM 34-81-1
Table H-4. Weather effects from temperature-
WEATHER
VALUE
(*'F/*'C)
SEVERE DEGRADATION
SYSTEM /EVENT
REMARKS
MODERATE DEGRADATION
SYSTEM/EVENT
REMARKS
LT -25/-32
TOW
DRAGON
Rocket launcher
IM202A1)
Handheld infrared
thermal viewer (PAS-7}
Dry cell battery
Personnel
Only 20%
effective
LT -20/-28
LT0/-18
LT 20/6
LT 32/0
GT 85/29
GT 95/35
Generators
NVS (PVS-4)
Maintenance
Personnel
See japp L
for water
consump
wo arctic
kit
wo Low
temp
adapter
Takes five
times
longer
Wheeled vehicles
Dry cell battery
Thermal night
observation device
IUAS-11)
Platoon early warning i wo
system (TRS-2)
j wo winter
I kit
I Only 40%
j effective
{ wo Arctic
j kit
I
1
I
DRAGON
BA3090
battery
Need low
temp
adapter
NVG (PVS-5)
Personnel
Small arms and
machine guns
wo Arctic
kit^
See |app"D
for wina-
chill
Effective-
ness
reduced
Personnel
See |app L
for neat
effects
Dry cell battery
I Will not
I hold
charge
H-6
FM 34-81-1
Table H-5. Weather effects from precipitation.
WEATHER
CONDITION
Light rain
or snow
SEVERE DEGRADATION
SYSTEM/EVENT
REMARKS
MODERATE DEGRADATION
SYSTEM/EVENT
REMARKS
Mortar operations
Wheeled vehicles
Sight glass
fogs up
Moderate
rain or
snow
Wheeled vehicles
LOS
Personnel movennent
Target acquisition
Platoon warning system
(TRS-2)
GSR
Acoustic systems
Equipment storage
Laser systems
Heavy
rain or
snow
Mortar operations
Personnel movement
Laser systems
LOS communications
Target acquisition
Thunder-
storm/
lightning
GSR
Ammunition
Refueling
Communications
Equipment storage
Safety
I Interference
Light
freezing
rain
Personnel
Wheeled vehicles
Moderate
freezing
rain
Personnel
Wheeled vehicles
SNOW
DEPTH
(INCHES>
GT3
Personnel movement
GT6
Personnel movement
20-mm and 40-mm
ammunition
Wheeled vehicles
GT 12
Wheeled vehicles
GT20
Tracked vehicles
GT30
Tracked vehicles
H-7
FM 34-81-1
APPENDIX I
WEATHER EFFECTS ON
INTELLIGENCE AND ELECTRONIC WARFARE
Intelligence operations, primarily sensors, are influenced by weather.
Collection and dissemination may be hindered by weather. All-source processing
requires evaluation of all weather conditions as they impact enemy and friendly
operations and systems. Listed below are other weather effects for lEW
operations that are not listed in the WTDA tables.
CLOUDS AND SKY COVER. Overcast skies with low cloud bases reduce the
effectiveness of infrared and photographic collection systems, and may restrict the use of
UAVs.
ICING. In addition to icing conditions associated with aircraft, ice is also a problem with
electronic systems that depend on ice-free antennas for optimum operation.
ILLUMINATION. NVD require about a quarter (23 percent) of the moon, 30 degrees
abo ve the horizo n, scattered clouds, and the sun more than 5 degrees below the horizon.
See I Appendix F] for further information.
PRECIPITATION. Even moderate amounts of rain and snow will obstmct vision and
degrade photographic and infrared collection systems. Heavier amounts of rain can
generate background electronic noise that reduces the efficiency of GSR.
SURFACE WIND. Strong winds may damage or prevent erection of system antennas.
TEMPERATURE. Frozen soil increases the difficulty of grounding equipment. At
extreme cold temperatures cables snap and wire is unmanageable. Extreme cold also
shortens battery life and may put systems requiring a good source of battery power out of
service.
VISIBILITY. Low visibility decreases the effectiveness of visual, photographic, infrared,
and E-O collection systems. However, LRSU's may benefit from restricted visibility and
increase their infiltration success. This condition may affect visual, laser range finding, and
target acquisition systems.
H
FM 34-81-1
Table 1-1. Weather effects from cloud ceilings.
WEATHER
VALUE
(FEET)
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT | REMARKS
SYSTEM/EVENT j REMARKS
LT50
NOE 1 Flight
UAV, any terrain 1 operations
LT300
IROQUOIS (EH-IH), flat | Below VFR
terrain i minimums
1
1
NOE 1 Flight
1 operations
UAV, flat terrain j
LT500
MOHAWK (0V/RV-1D) and • Below VFR
BLACKHAWK (EH-60A), i minimums
mountain terrain or night, i
flat terrain |
1
1
NOE i Target
1 require-
1 ments
UAV, flat or I
mountain terrain !
LT 1,000
IROQUOIS (EH-1H), j Below VFR
mountain terrain } minimums
1
1
1
1
NOE j Right
i operations
UAV, mountain I
terrain !
Army aviation I See
appE
1
1
1
1
1
1
1
'
1
1
1
1
1
1
1
1
1
1
1
1
1
»
1
1
1
1
1-2
FM 34-81-1
Table 1-2. Weather effects from reduced visibility.
WEATHER
VALUE
(METERS)
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT ! REMARKS
SYSTEM/EVENT ! REMARKS
LT800
BLACKHAWK (EH-60A) j Below VFR
and IROQUOIS (EH-1H), i minimums
daytime, flat or mountain I
terrain j
LT 1,000
Engagement collection i
plans, photographic 1
missions j
LT 1,600
Aircraft daytime, flat i Below VFR
terrain I minimums
LT 2,000
UAV 1
Engagement, collection i
plans, photographic i
missions j
LT 3,200
Aircraft nighttime, flat 1 Below VFR
terrain [ minimums
LT 4,800
Aircraft nighttime, ! Below VFR
mountain terrain ] minimums
1-3
FM 34-81-1
Table 1-3. Weather effects from surface winds.
WEATHER
VALUE
(KNOTS)
SEVERE DEGRADATION
SYSTEM/EVENT
REMARKS
MODERATE DEGRADATION
SYSTEM/EVENT
I REMARKS
GT7
Radars (PPS-5 and
PPS-15)
I Increased
I noise in tall
! grass
GT 13
Radio receiver
ITRR-20)
I Antenna
! must be
I guyed
GT 15
Acoustic sensors
MRDFS (PRD-10),
MANPACK (PRD-111
Radars (PPS-5 and
PPS-15)
j Less
I effective
DF
degraded,
antennas
degraded,
can't set
up
I Heavy vege-
tation
moved by
wind de-
grades
GT 15,
with
heavy
rain
MRDFS (PRD-101,
Man portable radio
receiving set (TRQ-30),
MANPACK (PRD-11)
j Exceeds
I system
! operating
j limits
GT 17, in
sand/
dust
HEXJAM (PLT-1A)
I Exceeds
! operating
I limits
GT 20
4-
Communications
antennas, radar
(PPS-5)
Antennas
degraded
+
GT 21 in
heavy
rain
Radio receiver
(TRR-20)
j Exceeds
I antenna
! operating
I limits
GT 25
Radar (PPS-15)
-I
I Cannot
I operate
! Antenna
I hard
■ to erect
TACFIX (TRQ-37) j DF degraded
GT30
SASS
TEAMMATE (TRQ-32)
TACJAM (MLQ-34)
PIRANHA (OG-181),
TACFIX (TRQ-37)
[ Antenna
I perfor-
1 mance
I Antenna
! erection
1-4
FM 34-81-1
Table 1-3. Weather effects from surface winds (continued).
WEATHER
VALUE
(KNOTS)
SEVERE DEGRADATION
SYSTEM/EVENT
REMARKS
MODERATE DEGRADATION
SYSTEM/EVENT
REMARKS
GT35
Countermeasures
system
(GLQ-3B), TEAMPACK
(MSQ-103C)
Antenna
mast
cannot be
fully
extended
TEAMMATE
(TRQ-32(V))
Countermeasures
system (GLa-3B)
PIRANHA (OG-181),
TEAMPACK
(MSQ-103C)
GUARDRAIL
(USD-9),
DP degraded
Antenna
extending
Antennas
should not
be erected
Antenna
operations
GT40
Personnel
Radar (PPS-5)
1 Antenna
4-
breaks
GT45
Acoustic sensors
lEW antenna systems
BLACKHAWK IEH-60A)
j Less
I effective
I
i Exceeds
I
4
limits
TEAMMATE
TRQ-32(V)),
TRAILBLAZER
(TSQ-114B(V))
DP degraded
4-
GT 50
Communications
antennas,
PIRANHA (OG-181),
TEAMMATE
(TRQ-32(V)},
REMBASS (GSQ-187)
Countermeasures set
(TLQ-15)
j Antenna
} should not
1 be erected
I Affects
j antenna
perfor-
mance
REMBASS
(GSQ-187)
PIRANHA (OG-181)
Radio receiver set
(TRR-20}
I Antenna
} perfor-
1 mance
I Antenna
I should not
! be erected
! Antenna
I damage
GT60
Fixed-wing aircraft
DRAGONFIX
(TSQ-164),
TRACKFINDER
(TSS-11)
May cancel
mis sion
(see fippT)
Exceeos
antenna
limits
4-
GT78
TRAILBLAZER
(TRQ-114B(V))
I Exceeds
! antenna
I limits
H
1-5
FM 34-81-1
Table 1-3. Weather effects from surface winds (continued).
GT90
GSM (TSQ-168), j Cannot
antenna j endure
j winds
1 above
1 100 kn.
j Weather
1 warning
j required
j at 90 kn.
1-6
FM 34-81-1
Table 1-4. Weather effects from temperature.
WEATHER
VALUE
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT • REMARKS
SYSTEM/EVENT j REMARKS
LT -25/-32
QUICK LOOK II i Exceeds
<ALQ-133) aircraft
limits
Countermeasure system Exceeds gen-
(GLQ-3B), erator op-
TACJAM (IVlLQ-34), erating
HEXJAM (PLT-1A) limits
TEAMPACKIMSQ-103C) Exceeds
battery
operating
limits
PIRANHA (OG-181) Requires
1 arctic
1 kit
Personnel I
Radar {PPS-5) j wo shelter
Radar <PPS-1 5) | wo genera-
1 tor, arctic
kit
TRAILBLAZER Carrier
{TSQ-114B(V)) requires
1 several
1 heater kits
1 to operate
j
LT -20/-28
1
Maintenance i Takes five
! times
I longer
LT0/-18
Radio receivers ■ Antenna
(TRR-20, TRR-33A) rotor
1 won't
! operate
Wheeled vehicles \ wo winter
kit
Dry cell battery ! Only 40%
! effective
Radar (PPS-15} ! Battery
I 5598
j required
LT 17/-9
Radars (PPS-5 and !
PPS-15) j
LT 20/-6
Platoon early | wo BA3090
warning system i battery
(TRS-2) I
OUTS ! Env system
! cannot
1 sustain
j personnel
LT 32/0
TACFIX (TRQ-37) !
Personnel ! Seelapp L
! foi^ wlnd-
j chill
Between
60/16
and
100/38
TRAFFICJAM j Transmit no
(TLQ-17A) I longer than
! 15
I continuous
1 minutes
1-7
FM 34-81-1
Table 1-4. Weather effects from temperature (continued).
WEATHER
VALUE
SEVERE DEGRADATION
MODERATE DEGRADATION 1
(•F/-C)
SYSTEM/EVENT
1 REMARKS
SYSTEM/EVENT
! REMARKS
GT 68/20
MAN PACK
(PRD-11)
1 Degrades
1 receiver
j accuracy
GT 80/27
GSM (TSQ-168),
shelter
1 Requires
1 internal
1 temp
1 remain
1 between
[ 65^F-80^F
GT 85/29
QUICKFIX
Affects lift
Personnel
See app L
(ALQ-151(V|)
tor temp/
MANPACK<PRD-11)
! Affects
receiver
accuracy
humidity
index
GT 95/35
Personnel
Dry cell battery
Will not hold
1 See app L
! for water
charge
j consumption
GT 100/38
TRAFFICJAM
(TLQ-17A)
Transmit no
longer
than 5
continuous
minutes
GT 1 20/49
QUICKFIX (ALQ-151),
GUARDRAIL (USD-9),
TACJAM (MLQ-34),
TRAILBLAZER
|TSQ-114B(V)),
TACFIX ITRQ-37)
Exceeds
limits
GT 1 25/52
Generators,
REMBASS
(GSQ-187),
TEAMPACK
(MSQ-103C),
PIRANHA (OG-1 81), '
TEAMMATE
{TRQ-32(V)), !
TRAILBLAZER, I
(TSQ-114B(V),) !
HEXJAM (PLT-1A)
Man portable radio 1
receiving set 1
(TRQ-30), j
Radars (PPS-5 and I
PPS-15) I
Exceeds
limits
BB-622
battery
degraded
1
j
1
1
1
1
1
1-8
FM 34-81-1
Table 1-5. Weatiier effects from precipitation.
WEATHER
CONDITION
SEVERE DEGRADATION
MODERATE DEGRADATION I
SYSTEM/EVENT ! REMARKS
SYSTEM/EVENT
' REMARKS
Light
rain
or snow
Wheeled vehicles
Moderate
rain or
snow
Wheeled vehicles j
LOS communications
Personnel movement
Laser systems
Target acquisition
Equipment storage
Platoon early warning
system (TRS-2)
Heavy
rain
or snow
Laser systems •
Personnel movement i
LOS communications 1
HEXJAM (PLT-1A) 1
TEAMPACK [
(MSQ-103C) 1
Target acquisition I
REMBASS (GSQ-187)
SLAR
Radars ( PPS-5 and
PPS-15)
GSM (TSQ-168),
antenna
Infrared de-
tection
People de-
tection
Must be
drained
when
exposed
to heavy
moisture
Heavy
rain
with
15 kn
or more
surface
wind
MRDFS (PRD-10) \
Man portable radio |
receiving set |
(TRQ-30) 1
MAINJPACK (PRD-11) j
GSM (TSQ-1 68) Must move
1 if rainfall
1 exceeds
I 4 inches/
! hour
Thunder-
storm/
lightning
Ammunition j
Radar (PPS-15) |
Aircraft operations I AR 95-1
Refueling operations I Safety
Communications j Interference
Equipment storage [
Light
freezing
rain
Aircraft wo deice j AR 95-1
Moderate
freezing
rain
Personnel movement |
Aircraft with deice j AR 95-1
1-9
FM 34-81-1
Table 1-5. Weather effects from precipitation (continued).
WEATHER
CONDITION
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT \ REMARKS
SYSTEM/EVENT \ REMARKS
Heavy
freezing
rain
Aircraft with deice » AR 95-1
1
>
SNOW DEPTH
(INCHES)
1
1
GT3
Personnel movement I
GT6
Personnel movement j
Wheeled vehicles I
GT 12
Wheeled vehicles I
1
GT20
Tracked vehicles I
GT30
Tracked vehicles I
1
I
I
1
1
•
HAIL
(INCHES)
1
1
Large hail
GT .5
GSM (TSQ-1 68) 1 Must be
1 protected
! from hail
1
1
1
1
t
1
1
1
1
1
1
1
1
1
I
1
1
1
1
1
I
1
1
1
1
1
1
1
1-10
FM 34-81-1
APPENDIX J
WEATHER EFFECTS ON
MECHANIZED INFANTRY
Mechanized infantry operations are also influenced by those weather
elements that degrade trafficability and visibility. Indeed, the weather effects
impacting mechanized infantry units will include most of the conditions that play a
role in both armor and regular infantry. Although the effect may be more
pronounced for mechanized infantry, armor, and cavalry operations, weather
elements have generally similar impacts on other units. Listed below are weather
effects for mechanized infantry that are not contained in the WTDA tables.
CLOUDS AND SKY COVER. Low overcast clouds will limit the effectiveness of aerial
illumination devices. Overcast clouds tend to limit heating of inactive targets and,
therefore, lower target detection range for thermal sights. NVD are limited by clouds
blocking natural light from the moon and stars. CAS and aerial resupply missions are
hindered by low clouds.
HUMIDITY. When coupled with high temperatures, humidity decreases effectiveness of
crews in closed vehicles.
ILLUMINATION. NVD require about a quarter (23 degrees) of the moon, 30 degrees
above the horizon, scattered clouds, and the sun more than 5 degrees below the h orizon.
Detailed products dealing with the use of E-0 devices are discussed in Appendix F.
PRECIPITATION. Rain and snow degrade trafficability, limit visibility, and degrade the
effectiveness of certain target acquisition and NVD.
STATE-OF-THE-GROUND. Wet grounds play an important role in the effectiveness of
chemical agents and smoke munitions. They can also affect trafficability and movement
rates. Frozen ground improves mobility and significantly increases time available for
preparing fighting positions. Deep snow slows movement of tracked vehicles. Frozen
ground affects systems such as mines, sensors, and indirect fire.
SURFACE WIND. Trajectory data and first round hit capability are degraded by high
crosswinds. Wind, or in some cases the lack of it, affects smoke and indirect fire
illumination missions and increases the number of indirect fire rounds used.
J-1
FM 34-81-1
TEMPERATURE. Too cold or too hot conditions dictate the type of lubricants to be
used, engine warm-up periods, and sustained rate of fire for weapons. High temperatures
decrease the time personnel can remain in vehicles. Extremely high temperatures increase
water consumption. Low temperatures degrade the ballistics of main guns. Extreme low
temperatures reduce personnel effectiveness, and decrease the availability of water
because of freezing. Temperatures changing from above to below freezing can freeze
stationary tracks into the mud. High temperatures cause gun tube "droop," shimmering,
mirages, and vehicle exteriors to be too hot to touch.
VISIBILITY. Poor visibility affects visual, laser range finding, and target acquisition
systems. Poor visibility increases the survivability of infantry units.
WINDCHILL. See Appendix L.
J-2
FM 34-81-1
Table J-1. Weather effects from cloud ceilings.
WEATHER
VALUE
(FEET)
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT ! REMARKS
SYSTEM/EVENT \ REMARKS
LT300
CAS j See|app E
LT 1 ,000
■
Army aviation, CAS, i See
app E
1
UAV j
1
J-3
FM 34-8 M
Table J-2. Weather effects from reduced visibility.
WEATHER
VALUE
(METERS)
LT 200
LT400
LT 500
LT 600
LT 800
LT 1,000
SEVERE DEGRADATION
SYSTEM/EVENT
FO
DRAGON
LT 1,200
LT 1,600
LT 2,000
LT 3,200
LT 4,500
LT 5,000
Tracked vehicle,
day operation
TOW
CAS
REMARKS
+
See|app E
MODERATE DEGRADATION
SYSTEM/EVENT
J REMARKS
LAW
NVG (PVS-5}
Infrared aiming light
(PAQ-4)
84-mm recoilless rifle
(AT-4)
NVS (PVS-2)
VIPER
FO
NVS (PVS-4)
DRAGON
DRAGON thermal sight
(TAS-5)
M-60 machine gun
7.62-mm coaxial
machine gun
NVS (TVS-2 and TVS-5) ]
Tracked vehicle,
day operation
.50-cal machine gun
NVS (TVS-4)
25-mm chain gun
M-60, M-1 main gun
TOW thermal sight
{UAS-12)
Handheld thermal
viewer (PAS-7)
Thermal night
observation
device (UAS-11)
CAS
81 -mm mortar
107-mm mortar (4>2 in)
J-4
FM 34-81-1
Table J-3. Weather effects from surface winds.
WEATHER
VALUE
(KNOTS)
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT 1 REMARKS
1
SYSTEM/EVENT ! REMARKS
LT 25
Incendiaries j
GT7
GSR ' Increased
j noise
GT 15
1
Acoustic sensors i Less
j effective
GT 15
Cross-
winds
TOW, i Impacts
DRAGON j tracking/
I reduces
j range
GT20
GSR ' Increased
! noise
1
Communication j
antennas i
NOE 1
GT 25
Personnel i
GT30
Helicopters [ May cancel
! mission
1
1
1
1
j See app E
GT 40
Personnel i
\
GT45
Acoustic sensors i Less
I effective
1
1
1
1
GT 50
Communication antennas .
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
\
»
1
1
J-5
FM 34-81-1
Table J-4. Weather effects from temperature.
WEATHER
VALUE
(°Fy°C)
SEVERE DEGRADATION
MODERATE DEGRADATION 1
SYSTEM/EVENT
! REMARKS
SYSTEM/EVENT
I REMARKS
LT -25/-32
TOW
DRAGON
Rocket launcher
(M202A1)
Handheld thermal
viewer (PAS-7)
Dry cell battery
Personnel
1 Only 20%
1 effective
Generators
Laser infrared
observation set
{GVS-5)
INF/CFV (M2/M3)
1 WO arctic
kit
1 wo
1 external
J power
! wo winter
j kit
LT -20/-28
NVS (PVS-4 and
TVS-5)
Maintenance
Tanks (M-1, M-60)
[ wo low
1 temp
1 adapter
j Takes 5
[ times
1 longer
j Accuracv
LT0M8
Wheeled vehicles
Dry cell battery
! wo winter
kit
! Only 40%
j effective
LT 20/-6
Thermal night
observation device
(UAS-11)
Platoon early warning
system {TRS-2)
DRAGON
j wo arctic
j kit
1 wo
1 BA3090
j battery
1 wo low
! temp
j adapter
LT 32/0
NVG (PVS-5)
Personnel
Small arms and
machine guns
j wo arctic
! kit
1 See app L
1 tor wina-
1 chill
1 Reduces
! effective-
1 ness
GT 85/29
Personnel
1 See app LI
GT 95/35
Personnel
Dry cell battery
1 Will not
! hold 1
! charge 1
1 See app L
GT 125/52
All NVS
81 -mm mortar
Generators
90-mm recoilless rifle
Laser infrared observing
set (GVS-5)
WP rounds
] Ammunition
1 Storage, use
J-6
FM 34-81-1
Table J-5. Weather effects from precipitation.
WEATHER
CONDITION
Light rain
or snow
Moderate
rain or
snow
Heavy
rain or
snow
Thunder-
storm/
lightning
Light
freezing
rain
Moderate
freezing
rain
SNOW
DEPTH
tINCHES)
GT3
GT6
GT 12
GT20
GT30
SEVERE DEGRADATION
SYSTEM/EVENT
REMARKS
Wheeled vehicles
Mortars
Personnel movement
LOS communications
Target acquisition
Laser systems
Personnel
Wheeled vehicles
Personnel movement
Wheeled vehicles
Tracked vehicles
MODERATE DEGRADATION
SYSTEM/EVENT
REMARKS
Mortars
Wheeled vehicles
Sight glass
fogs
LOS communications
Personnel movement
Target acquisition
Platoon warning
system (TRS-2)
GSR
Acoustic systems
Equipment storage
Ammunition
Refueling
Communications
Equipment storage
I Safety
I Safety
1 Interference
I
H
Personnel
Wheeled vehicles
Personnel movement
20-mm and 40-mm
ammunition
Tracked vehicles
J-7
FM 34-81-1
APPENDIX K
WEATHER EFFECTS ON
NUCLEAR, BIOLOGICAL, AND CHEMICAL OPERATIONS
NBC operations are extremely sensitive to environmental conditions that
affect the transport and diffusion of CB agents. Humidity, air temperature, ground
temperature, wind direction and speed, low-level temperature gradient,
precipitation, cloud cover, and sunlight are a few of the critical elements to
consider when planning NBC operations. The degree of impact depends upon the
synoptic situation and the local influence of topography, vegetation, and state-of-
the-ground.
The low-level stability of the atmosphere is an important factor in
determining whether there will be a good horizontal transport of radioactive or CB
clouds. However, stability is not measured directly but is calculated by considering
the above weather elements. The WETM or SWO will assist you in making a
stability determination. Listed below are weather effects for NBC operations that
are not contained in the WTDA tables.
CLOUDS AND SKY COVER, persistent overcast low clouds usually indicate a neutral
(favorable) condition, while broken low clouds indicate an unstable (unfavorable) condition
during the day and a moderately stable (favorable) condition at night.
HUMIDITY. Humidity has little effect on most chemical agents; however, high humidity
destroys some chemical agents such as lewisite and phosgene because of rapid hydrolysis.
High humidity increases the effectiveness of HC and phosphorous smokes, some chemical
agents, and both wet and dry forms of biological agents. High humidity improves the
effectiveness of wet aerosols by reducing evaporation while low humidity assists agent
aerosols. High humidity, combined with high temperatures, reduces time in which troops in
MOPP gear are effective.
PRECIPITATION. Rain and snow will effect the persistence of chemical agents and may
produce radioactive rainout and hot spots. Snow may cover and neutralize certain liquid
agents. Rain may even work as a decontaminate. On the other hand, some agents may be
very persistent on snow.
STATE-OF-THE-GROUND. Soil conditions impact the effectiveness of chemical agents.
Bare, hard ground favors short-term effectiveness and high- vapor concentrations. If the
surface is porous, such as sand, the hquid agent quickly soaks in. Vegetative cover
K-1
FM 34-81-1
reduces exposure to ultraviolet light and favors the survival of wet aerosols. Wet soil
degrades the effectiveness of smoke munitions.
SUNLIGHT. A bright sun will shorten the hfespan of biological agents. Sunhght also
plays a role in temperature gradients, winds, and temperature (stability).
TEMPERATURE. Some agents are more persistent at low temperatures. Vaporization
may be a problem with higher temperatures. Normal atmospheric temperatures have little
direct effect on a biological agent aerosol. Sub-freezing temperatures make water-based
decontamination methods ineffective.
THUNDERSTORMS AND LIGHTNING. Severe electrical storms will restrict
munitions handling because of safety.
WINDS. Winds play a significant role in CB agent dispersion, chemical agent persistence,
and aerial dehvery methods. Very light and strong winds degrade effectiveness of smoke
and NBC operations. Wind direction is considered for fallout pattern determination.
K-2
FM 34-81-1
Table K-1. Weather effects from cloud ceilings.
WEATHER
VALUE
iFEET)
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT I REMARKS
SYSTEM/EVENT I REMARKS
LT600
Nuclear burst j Absorbs/
I scatters
! 90% of
1 thermal
energy
LT 5,000
Nuclear burst * Burst above
I clouds re-
duces
thermal
! and EMP
1 effect
Nuclear burst \ Burst below
I clouds en-
j hances
' thermal
effect
K-3
FM 34-81-1
Table K-2. Weather effects from reduced visibility.
WEATHER
VALUE
(METERS)
SEVERE DEGRADATION
MODERATE DEGRADATION \
SYSTEM/EVENT 1 REMARKS
SYSTEM/EVENT
REMARKS
NO VALUES IDENTIFIED I
!
K-4
FM 34-81-1
Table K-3. Weather effects from surface wind.
WEATHER
VALUE
{KNOTS)
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT •' REMARKS
SYSTEM/EVENT REMARKS
Calm
Chemical agents »
Smoke employment j
LT2
Chemical agents j
LT5
Smoke employment j
LT 10
Smoke employment, j Wind
chemical agents ! direction
j more
1 critical
GT 19
Smoke employment | Wind
{ direction
1 more
1 critical
GT25
Personnel j See app L
GT30
Chemical agents j Wind
1 direction
! more
1 critical
GT40
Personnel j See lapp L|
K-5
FM 34-81-1
Table K-4. Weather effects from temperature.
WEATHER
VALUE
(op/oC)
SEVERE DEGRADATION
MODERATE DEGRADATION |
SYSTEM/EVENT 1 REMARKS
SYSTEM/EVENT
REMARKS 1
LT -25/-32
Chemical detection i Becomes
1 ineffective
LT -20/-28
Protective mask i wo winter
1 kit
LT-15/-25
Chemical } Solution
decontamination ! becomes
(DS-2) ! ineffective
Detector (battery I
operated) j
LT +32/0
Chemical detection [
Chemical I
decontamination j
LT 40/3
Nerve agent antidote | Protect
1 against
! low ternp
GT 80/26
Personnel i See app L
1 for M0PP4
GT 95/35
Chemical <
evaporation |
GT 110/39
Chemical !
decontamination j
GT 120/48
Smoke generator ]
K-6
FM 34-81-1
Table K-5. Weather effects from precipitation.
WEATHER
CONDITION
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT ! REMARKS
SYSTEPv1/EVENT 1 REMARKS
Light rain
or snow
1
Chemical agents j Wash into
1 low areas
Nuclear burst j Absorb/
j scatter
! up to
i 90%
1 thermal
energy
Moderate
rain or
snow
Engine-generated j
smoke |
Heavy rain
or snow
Chemical agents | Wash into
! low areas
Nuclear burst j Absorb or
j scatter
j up to 90%
j thermal
I energy
Engine-generated smoke j
Thunder-
storm/
lightning
Chemical |
Smoke |
SNOW
DEPTH
(INCHES)
GT3
WP smoke rounds 1
K-7
FM 34-81-1
APPENDIX L
WEATHER EFFECTS ON PERSONNEL
Weather has a great impact on the soldier, particularly extreme
temperatures. It may have a more immediate impact on the human body than on
systems and equipment. Each soldier is unique because of differences in physical
conditioning or a higher tolerance to hot and cold temperatures.
Regardless of physical differences, temperature, surface wind speeds, and
relative humidity affect everyone to a degree. This is particularly true for physical
activity, personal protection, and water consumption.
The products and information you develop as part of this appendix should be
included in all weather effects briefings prepared for the commander and staff.
COLD WEATHER ENVIRONMENT
A soldier's greatest concern in extreme cold is survival. Soldiers spend
much of their time trying to keep warm and protecting exposed skin from frostbite.
Cold temperatures and wind speed create a windchill factor which has a definite
effect on the soldier.
Your weather forecast includes temperatures in degrees Fahrenheit and wind
speed in nautical miles-per-hour (knots). I Table L-H lets you use temperatures in
Fahrenheit and wind speed either in statute miles or knots to determine windchill
values and effects.
Extreme cold results in an increase of water consumption by soldiers. This
is due to working outdoors in heavy clothing and the dry air that usually
accompanies cold weather.
Wind and cold effects on military free-fall parachutists must be taken into
account when planning these kinds of operations.
L-1
FM 34-81-1
AMBIENT AIR
Ambient air temperatures at high altitudes can be calculated using the
standard temperature lapse rate of 2°C (3°F) for every thousand feet increase
AGL. For example, a military free fall jumpmaster spotting an aircraft at 25,000
feet AGL where the ground temperature is 50° F would be jumping into an air
temperature of -25° F (calculated at 50 °F-(25 x 3°F)).
WINDCHILL FACTOR
The windchill caused by the speed of the aircraft (130 kn) increases the
problems for the jumpmaster. Parachutists in free fall attain a terminal velocity of
120 mph. Parachutists conducting HAHO operations can be under canopy for as
long as 35 to 40 minutes, and be exposed to bone-numbing cold temperatures as
they descend. To succeed, they must be equipped to withstand these harsh
conditions.
L-2
FM 34-81-1
Table L-1. Windchill chart.
WIND
SPEED
(KNOTS)
WIND
SPEED
(MPH)
LOCAL TEMPERATURE (°F)
32
23
14
5
-4
-13
-22
-31
-40
-49
-58
EQUIVALENT TEMPERATURE (°F)
CALM
32
23
14
5
-4
-13
-22
-31
-40
-49
-58
4
5
29
20
10
1
-9
-ia
-28
-37
-47
-5fi
-65
9
10
18
1
-4
-15 1
-26
-37
-48
-59
-70 1
-81
-91
1-^
1H
l.T
-1
-13
-9R
-37
-49
-fil
-7:^
-Rc;
-q7
-inq
17
20
7
-6
-19
-32
-44
-57
-70
-83
-96
-109
-121
21
25
3
-10
-24
-37
-50
-64
-77
-90
-104
-117
-127
26
30
1
-13
-27
-41
-54
-68
-82
-97
-109
-123
-137
30
35
-1
-15
-29
-43
-57
-71
-85
-99
-113
-127
-142
.-^c;
AC\
-rt
-17
-.-^1
-A^
-f;q
-74
-R7
-107
-11R
-l.*^!
-14R
.-^9
4B
-T
-17
-y.^
-4R
-Rq
-74
-R7
-in?
-llfi
-131
-14Fi
A1\
Rn
-4
-Ifl
.^7.
-47
-RC?
-76
-qi
-inFi
AOCS
-L34
-14fi
LITTLE
DANGER FOR
PROPERLY
CLOTHED
PERSONS
CONSIDERABLE
DANGER
VERY
GREAT
DANGER
DANGER FROM FREEZING OF EXPOSED FLESH
HOT WEATHER ENVIRONMENT
In hot weather the important factors are temperature and relative humidity.
The Soldiers' primary concerns are physical exhaustion and dehydration. You must
consider both because a common work task will take longer and additional water
may have to be transported during hot weather. The following hot weather
concerns play a role in the employment of soldiers.
WATER ADEQUACY. Water supplies and the enforcement of its intake before, during and
after physical activity is critical for survival.
WORKLOAD CORRELATION. Workload or training activities must be adapted to
environmental heat stress conditions.
REST PERIODS. Adequate break time must be provided for physically active personnel in a
hot environment.
L-3
FM 34-81-1
CHILLED DRINKING WATER. Soldiers will often reject warm drinking water even when
they are significantly dehydrated.
ADJUST PHYSICAL ACTIVITY. Soldiers' introduction to physical exertion in a hot
climate upon arriving from a temperate one should be as gradual as circumstances allow. They
will need 1 to 2 weeks' time to physiologically adjust to the new climate. Lighten physical
activity during this period to ensure optimum performance.
SALT. Sodium intake must be maintained in hot weather. Two good meals a day normally
provide enough salt for most soldiers.
HUMIDITY. This can be tricky. A low WBGT index (for example, in the morning) may not be
a totally safe indicator if the humidity is high. High humidity retards cooling by evaporation of
sweat, and decreases the urge to drink sufficient water.
WATER SPRAY. A water mist will cool a person off. But it should never be substituted for
adequate consumption of water before, during, and after strenuous activities in the heat.
Tables are provided that use a temperature measurement (or temperature
forecast) and a relative humidity calculation. The SWO can routinely provide you
v^ith temperature and relative humidity forecasts. If you need air temperature
values measured at your particular location, use the thermometer included in the
FALOP BWK.
HOT WEATHER WATER REQUIREMENTS
Table L-21 shows the water needs (in quarts per day) for soldiers at 3 activity
levels over an 8-hour work period. To determine soldiers' average v^ater needs,
you have to know the air temperature and decide the level of activity the troops
will be doing. For example, if a soldier is doing 8 hours of hard work in the sun
(curve C) when the average temperature for the day is 100°F, his water
requirements for the day will be around 15 quarts.
This amount of water can be converted into extra weight the soldier must
carry. One quart is equal to 2 pounds so the 15 quarts of water would weigh
30 pounds.
L4
FM 34-81-1
Table L-2. Daily water consumption requirements
for three levels of activity.
WATER
CONSUMPTION
IN
QUARTS
25
20
15
10
5
A. HARD WORK IN THE SUN
(Crawling with equipment on)
B. MODERATE WORK IN THE
SUN (Cleaning wpn and equipment)
C. REST IN THE SHADE
60 70 80 90 100 110 120
TEMPERATURE IN DEGREES FAHRENHEIT
HOT WEATHER WORK TIME LIMITS
Table L-3| shows the time limits during which work can be safely performed in
hot weather. In computing the time limits, both air temperature and relative
humidity are considered. The values are based on a sitting soldier in BDUs doing
light work.
The table gives an estimate of the length of time continuous work should be
performed. For moderate work a technical manual on the PATRIOT missile system
recommends that you sue on-half the values contained in the table. You should
not consider these tables as absolute limits--especially since light, moderate, or
heavy work are difficult to quantify,
based on the WBGT index.
Table L-4 indicates work time in hot weather
L-5
FM 34-81-1
Table L-3. Work time in hot weather operations.
TEMPERATURE
RELATIVE HUMIDITY (%)
rc)
(°R
10
30
50
70 90
100
60
140
1 HR
.25 HRS
54
130
2HRS
.5 HRS
.25 HRS
NO WORK RECOMMENDED
49
120
4HRS
2 HRS
.5 HRS
.25 HRS
43
110
12 HRS
4 HRS
2 HRS
.5 HRS
.25 HRS
38
100
NO LIMIT
12 HRS
4 HRS
2 HRS
1 HR
.5 HRS
32
90
WITH PRECAUTIONS
12 HRS
6 HRS
4 HRS
Table L-4. Wet bulb globe temperature index {light work).
HEAT
CONDITION/
CATEGORY •
WET BULB GLOBE
TEMPERATURE INDEX
(DEGREES F)
WATER INTAKE
QUARTS/HOUR
WORK/REST CYCLE
(MINUTES)
1
78.0 to 81 .9
AT LEAST 1 /2
CONTINUOUS
2
82.0 to 84.9
AT LEAST 1.2
50/10
3
85.0 to 87.9
AT LEAST 1
45/15
4
88.0 to 89.9
AT LEAST 1 1 /2
30/30
5 *•
90.0 and ABOVE
MORE THAN 2
20/40
* MOPP GEAR OR BODY ARMOR ADDS AT LEAST 10 DEGREES F TO THE WPGT INDEX.
♦* SUSPEND PHYSICAL TRAINING AND STRENUOUS ACTIVITY. IF OPERATIONAL (NON-
TRAINING) MISSION REQUIRES STRENUOUS ACTIVITY, ENFORCE WATER INTAKE TO
MINIMIZE EXPECTED HEAT INJURIES.
L-6
FM 34-81-1
APPENDIX M
WEATHER EFFECTS ON SPECIAL OPERATIONS FORCES
Special operations forces (SOFs) consist of Special Forces (SF), Rangers,
special operations aviation, psychological operations (PSYOP) and Civil Affairs
(CA), as well as signal and support. These operations are influenced by many of
the same elements and thresholds as their conventional counterparts. However,
special tactics and capabilities can make SOF operations more weather sensitive
than conventional operations.
SOF optimal use is in deep operations at the strategic or operational level.
These operations are significantly affected by both weather and environmental
conditions, and make extensive use of climatology. The following are some of the
more significant weather effects for SOF operations.
CLOUDS AND SKY COVER. Low clouds improve SOF mobility due to decreased chance
of detection. Low clouds may degrade target acquisition. Employment of E-0 systems (both)
infrared and laser) may be degraded.
HUMIDITY. Moist air degrades sound propagation while dry air improves it. Prolonged
exposure of sensitive equipment (C-E and medical) affects maintenance requirements and the
useful life of supplies.
ILLUMINATION. Poor light conditions enhance surreptitious operations but hinder visual
observation of targets, troop movement, and both land and sea navigation. Special operations
aviation generally operates at night.
PRECIPITATION. Rain or snow may improve surreptitious ground mobility if threat patrols
seek shelter. Aircraft and watercraft can "hide" in, or be masked by, precipitation to avoid
radar detection. Wet weather improves crowd control, but during prolonged precipitation may
increase populace restlessness. Heavy rain or snow affect CA operations. Moderate rain
dampens sound during loudspeaker operations. Variations from normal precipitation can alter
the speed of river stream flow and estuary currents.
REDUCED VISIBILITY, poor visibility comphcates target surveillance. Surreptitious
movement is enhanced. The ability to navigate and fly at night is degraded. Selected E-0
systems are degraded (se q Appendix F| ). Restricted visibility aloft affects flight operations.
SOLAR AND IONOSPHERIC DISTURBANCES. High sun spot activity degrades
long-haul communications and PSYOP radio and television broadcasts.
M-1
FM 34-81-1
SURFACE WIND. Wind speed and direction forecasts (both surface and aloft) are critical to
leaflet dissemination. Wind also cuts down on loudspeaker sound propagation. Moderate
winds can degrade or enhance waterborne operations, depending on situation. Winds are a
major cause of turbidity in shallow water. Winds affect CA operations according to each
particular type mission.
TEMPERATURE. Both high and low temperatures may affect crowd and population control.
Extreme cold may improve surreptitious mobility if threat guards and patrols seek shelter. Cold
air allows better sound propagation than warm air.
TIDES AND CURRENTS. Infiltration and exfiltration route planners must consider timing
and height of tides. Infiltration at low tide results in more exposure while moving up the beach
and may require avoiding obstacles in shallow water. In both inland and open waters, currents
may vary widely and require careful study.
M-2
FM 34-81-1
Table M-1. Weather effects from cloud ceilings.
WEATHER
VALUE
(FEET)
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT 1 REMARKS
SYSTEM/EVENT ! REMARKS
LT200
R&S ! Target
j acquisition
1
LT300
Ground 1 Target
j acquisition
1
1
1
LT 1,000
Airborne, CAS j Aircraft
! fast movers
HALO Infiltration I Minimum
1 base of
1 cloud over
i DZ
Amphibious j CAS
Aviation j Target
I acquisition
Ground j CAS
1
Aviation I See app E
1
Ground, R&S ! Target
1 acquisition
1
1
!
LT 3,000
1
1
1
i
1
1
1
1
Airborne j Aircraft
Amphibious j CAS
Aviation j Target
I acquisition
Ground ! CAS
LT 3,500
r
1
1
1
1
I
1
1
1
j
CAS 1 Depends on
! tactics"
j fast
! movers
LT 4,500
HERCULES (AC-130) 1
1
1
1
LT 5,000
NBC 1 Blast effect
1
1
1
MAVERICK I Depends on
1 tactics
1
1
1
1
1
1
1
1
i
\
r
1
1
1
1
1
1
1
1
1
M-3
FM 34-81-1
Table M-2. Weather effects from reduced visibility.
WEATHER
VALUE
(METERS)
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT [ REMARKS
SYSTEM/EVENT '• REMARKS
LT 1,600
Airborne | Aircraft
I operations
Amphibious j Target
[ acquisition
Aviation j Target
1 acquisition
R&S j Target
j acquisition
NBC 1 Target
! acquisition
1
1
1
1
r
1
1
1
(
1
1
1
1
J
1
— 1
LT 4,800
Airborne | Aircraft
I operations
Amphibious j Target
1 acquisition
Aviation j Target
1 acquisition
R&S ! Target
j acquisition
NBC I Target
I acquisition
1
1
1
1
1
{
1
1
t
' — 1
I
1
— 1
1
1
1
1
1
1
1
1
1
1
\
1
1
1
M-4
FM 34-81-1
Table M-3. Weather effects from surface winds.
WEATHER
VALUE
(KNOTS)
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT I REMARKS
SYSTEM/EVENT ! REMARKS
SURFACE
WINDS
1
LT3
NBC j Agent
j dispersal
GT7
j
j
Amphibious Sea state
NBC Agent
dispersal
Balloon launch for !
leaflet dissemination
GT 10
NBC 1 Agent
j dispersal
GT 13
Static line (infil) j Chute
I limitation
GT 15
Airborne ! Jump
j release
Loudspeaker broadcasts [
GT 18
RAP 1 Chute
j limitation
GT20
Airborne 1 Jump
I release
GT25
Aviation j Aircraft
Signal j Antenna
j stability
GT30
Aviation j Aircraft
GT35
Amphibious j Sea state
GT49
Signal j Antenna
[ stability
GUST
SPREAD
GT 15
Aviation 1 Aircraft
M-5
FM 34-81-1
Table M-3. Weather effects from surface wind (continued).
WEATHER
VALUE
(KNOTS)
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT 1 REMARKS
SYSTEM/EVENT 1 REMARKS
UPPER
AIR WINDS
GT 15
Airborne i Jump
1 release
GT20
Airborne i Jump
[ release
M-6
FM 34-81-1
Table M-4. Weather effects from temperature.
WEATHER
VALUE
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT 1 REMARKS
SYSTEM/EVENT '■ REMARKS
LT -25/-37
Signal i Exposure
LT0/-18
Signal | Exposure
LT 25/-4
Amphibious ' Exposure
Logistics ] Exposure
LT 32/0
Amphibious i Exposure
Signal i Exposure
GT 68/20
NBC j Dispersal
1 persis-
1 tence
GT 95/35
NBC i Dispersal,
i persis-
1 tence
Signal j Heat
I stress
GT 105/41
Signal 1 Heat
» stress
GT 122/50
Logistics j Storage
M-7
FM 34-81-1
Table M-5. Weather effects from precipitation.
WEATHER
CONDITION
RAIN
(INCHESI
Any
Light rain
{trace -
.1/hour)
Moderate
rain (.1 1
to
.3/hourl
LT -B/hour
GT .5/hour
Freezing
precipi-
tation
SEVERE DEGRADATION
SYSTEM/EVENT
REMARKS
NBC
Airborne
Amphibious
Ground
R&S
SNOW
DEPTH
(INCHES)
Trace
GT 1
Signal
Aviation
Signal
GT24
Aviation
Logistics
Ground
R&S
I Agent
4-
persistence
Fall rate
Beach state
Trafficability
Trafficability,
target
acquisition
MODERATE DEGRADATION
SYSTEM/EVENT
REMARKS
Airborne
Amphibious
Ground
R&S
Attenuation
I Aircraft icing
I Antenna
1 stability
I
t Targeting,
Signal
Aviation
+
vertigo
Trafficability
Trafficability
Trafficability
Ground
R&S
Logistics
Aviation
+
Fall rate
Beach state
Trafficability
Trafficability,
target
acquisition
I Attenuation
I Target
i acquisition
1 Trafficability
I Trafficability
[ Trafficability
! Targeting,
j vertigo
M-8
FM 34-81-1
Table M-6. Weather effects from miscellaneous causes.
WEATHER
CONDITION
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT
I REMARKS
SYSTEM/EVEIMT ! REMARKS
THUNDER-
STORMS
1
LT5 km
distance
Airborne
Aviation
R&S
Logistics
NBC
Signal
1 Aircraft
j Aircraft
j Ground
j Storage
1 Munition
i storage
I System
I safety,
1 ground
! operations
1
1
1
1
t
1
i
1
1
GTBkm
distance
Airborne | Aircraft
Aviation | Aircraft
R&S j Ground
j operations
Logistics i Storage
NBC ! Munition
! storage
Signal I System
! safety,
1 ground
I operations
bM-bCIIVE
ILLUMI-
NATION
(MILULUX)
1
1
LT2.5
Airborne
Amphibious
Aviation
R&S
Signal
1 NVG
! NVG
1 NVG
1 NVG
j NVG
1
1
1
t
r
i
1
RELATIVE
HUMIDITY
1
1
GT 70%
Logistics
1 Storage
1
1
r
1
1
1
1
1
J
1
1
1
1
1
1
M-9
FM 34-81-1
Table M-6. Weather effects from miscellaneous causes (continued).
WEATHER
CONDITION
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT ! REMARKS
SYSTEM/EVENT ! REMARKS
DENSITY
ALTITUDE
(FEtn
4,000
Airborne, Aviation 1 Aircraft lift
6,900
Airborne, Aviation I Aircraft lift
SEA STATE
IFEET)
Tide
GT 6
Amphibious j Boat safety
Swell-
height
GT3
Amphibious j Boat safety
Surf height
GT4
Amphibious j Boat safety
AIRCRAFT
ICING
Trace
Aviation ! Aircraft
I safety
Light or
greater
Aviation j Aircraft
1 safety
AIRCRAFT
TURBU-
LENCE
Light
Aviation I Aircraft
j safety
Moderate
Aviation I Aircraft
I safety
LAPSE
RATE
Inversion
Signal '' Fading,
1 ducting
NBC ! Agent
1 persis-
j tence
M-10
FM 34-81-1
Table M-6. Weather effects from miscellaneous causes (continued).
WEATHER
CONDITION
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT | REMARKS
SYSTEM/EVENT 1 REMARKS
Stability
change
NBC I Agent
1 persistence
IONOSPHERIC
DISTURBANCE
Any
Signal i Frequency
1 use
M-11
FM 34-81-1
APPENDIX N
PARTI
WEATHER EFFECTS ON THREAT SYSTEMS
MILITARY ASPECTS OF WEATHER
Because of recent significant political and military changes in the former
Soviet Union, US Forces will have to be prepared to fight in a variety of climatic
conditions on short notice. One major key to accomplishing our missions under
these circumstances is understanding how weather affects both friendly and threat
forces and their operations, systems, and personnel.
Current weather conditions and weather forecasts for the AO and AI are
analyzed to determine the effects on friendly and enemy operations. This is
especially significant when threat forces have the capability to employ NBC
weapon systems.
THREAT EOUIPMENT
Some of the major arms producers and sellers in the world today are the
former Soviet Union, Sweden, Brazil, Britain, Germany, France, Italy, and the
United States. However, the major arms purchasers continue to be the
undeveloped or Third- World countries in the Middle East, Latin America, and Asia.
The types of threat equipment that we may encounter on future battlefields
will vary considerably from artillery and mortars produced during World War II to
the Austrian-produced GHN-45, a 155-mm towed gun with a range of 39,600
meters (using extended-range full-bore-base bleed (ERFB-BB) technology). Almost
all of the Third- World countries have bought or made their own versions of Soviet-
produced tanks, APCs, artillery, antiaircraft artillery (AAA), and assorted surface-
to-air (SAM) and surface-to-surface missile (SSM) systems.
N-1
FM 34-81-1
CRITICAL WEATHER FACTORS
The following are major critical weather factors that can enhance or degrade
combat operations, systems, and personnel.
LOW VISIBILITY. Low visibility (less than 3 km) can be beneficial to both threat and
friendly forces. It conceals the center of gravity and maneuver of offensive forces and
increases the possibility of achieving surprise. Some disadvantages of low visibility are that
it hinders C^and reduces the effectiveness of R&S and target acquisition-especially during
the defense.
SURFACE WINDS. Strong winds can reduce the effectiveness of downwind forces by
blowing dust, smoke, sand, rain, or snow on them. The upwind force generally has better
visibility and can advance faster and easier. Strong winds also limit airborne and aviation
(primarily hehcopters) operations. Winds in excess of 35 knots can cause personal injury,
damage materiel and structures, create false radar returns, and reduce visibility because of
blowing sand, dust, and other battlefield debris.
PRECIPITATION. Precipitation is significant because it affects trafficability, visibility,
personnel effectiveness, and a wide variety of tracked and wheeled military equipment.
Heavy rains can make some unsurfaced, low-lying, and off -road areas impassable. In
addition, both rain and snow can drastically reduce personnel effectiveness by limiting
visibility, causing discomfort, increasing fatigue, and creating other physical and
psychological problems.
CLOUD COVER. The type and amount of cloud cover and the altitude of cloud bases
and tops influence aviation operations. CAS employing fixed- wing aircraft would like a
ceiling of at least 2,500 feet (762 m), but can be employed with ceilings as low as 500
feet. Threat CAS rotary-wing aircraft and aerial resupply missions require a minimum
ceiling of 300 feet (100 m). Cloud cover affects ground operations by reducing illumination
and visibility, or, in some instances, by enhancing the effects of artificial hght.
TEMPERATURE AND HUMIDITY. Together, these elements have a direct impact on
personnel and vehicle performance. Excessively high temperatures cause heat-related
injuries to personnel and vehicle engine wear that leads to equipment failure. Very low
temperatures increase cold weather injuries, cause damage to vehicle cooling systems and
engines, decrease the effectiveness of vehicle lubrication, and create excessive logistics
requirements.
N-2
FM 34-81-1
Table N-1. Weather effects from cloud ceilings.
WEATHER
VALUE
(FEET)
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEWl/EVENT 1 REMARKS
SYSTEM/EVENT ! REMARKS
LT 1 ,000
SA-9 SAM 1
SA-1 4 SAM !
LT 2,500
ZU-23 i
ZSU-23-4 1
SA-1 3 (Contrast j
mode) j
SA-1 6 I
SA-1 9 !
N-3
FM 34-81-1
Table N-2. Weather effects from reduced visibility.
WEATHER
VALUE
(METERS)
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT I REMARKS
SYSTEM/EVENT ! REMARKS
LT200
RPG-1 8 (rocket | ATW
launcher) j Rifle
AKM/AKMS {7.62-mm) | E-0 device
TKN-1T infrared periscope |
1
LT 500
SA-14 GREMLIN SAM |
SA-13SAM 1
SA-16SAM !
SA-19 (FSUI SAM 1
0U-3GK White infrared \ E-0 device
search light |
RPG-7 (Grenade launcher) | ATW
PT-76 (5.45-mm) ! AG/LT
AK-74 j Rifle
1
1
LT600
ERYX
LT750
SA-9 GASKIN SAM j
1
1
LT800
AT-2 SWATTER j
AT-3 SAGGER j ATGM
AT-6 SPIRAL 1 ATGM
1 ATGM
ASU-85 j AG/LT
BMD (73-mm) | LAV
BMP (73-mm) I LAV
Sniper rifle, SVD ! Rifle
RPK-74, squad MG j MG
AGS-17, grenade launcher j
RPG-16, grenade launcher |
LT 1,000
All Types \ ATGM
1
SPG-9 (73-mm recoilless \ ATW
rifle) 1
SD-44 (85-mm) ! ATW
14.5-mm KPU hvy MG ! AA
7.62-mm PKT MG j AA
DShK 1 AA
NSV/NSVT 1 MG
PK Series 1 MG
MT-LB j LAV
7.62-mm coaxial machine j MT
gun for all tanks |
1
1
1
1
1
1
\ _
1
1
1
1
1
1
1
1
N-4
FM 34-81-1
Table N-2. Weather effects from reduced visibility (continued].
WEATHER
VALUE
(METERS)
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT [ REMARKS
SYSTEM/EVENT | REMARKS
LT 1,500
1
I
1
)
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
7.62-mm MG |
15.5-mm heavy MG j
gun 1
BTR-50,-60,-70 ! AA/LAV
(14.5-mm) !
KPVT ! AA
ACRV Ml 974 1 LAV
DShK ! MG
NSV/NSVT MG
T-54, T-55. T-62 (main | MT
gun) 1
LT 2.000
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
T-12, MT-12 (lOO-mm) ] ATW
KPVT ] MG
BRDM-2 (14.5-mm) | LAV
T-80, T-72, T-64 (main | MT
gun) j
MATHOGO ]
MILAN 2 1
R8S-56 SPIGOT |
LT 2,500
1
1
1
1
1
SA-7 GRAIL j FSU SAM
ZU-23 j AA
ZSU-23-4 1 AA
LT 3,000
1
1
1
1
1
1
RED ARROW 73 \
RED ARROW 8 |
SUSONGP'O 1
AT-3 SAGGER |
LT 4,000
1
1
1
1
1
I
1
t
t
^
1
t
I
SA-9 GASKIN |
HOT 2 1
SWINGFIRE 1 FSU SAM
AT-2 SWATTER |
AT-5 SPANDREL |
AT-8 SONGSTER |
AT-10 STABBER j
SA-13 (Contrast Mode) | FSU SAM
LT 4,500
1
1
MA PATS !
LT 5,000
I
1
1
1
1
1
1
1
i
NIMROD ] ATGM
AT-6 SPIRAL ]
AT-11 SNIPER [
SWIFT (SF) 1
LT 6,000
I
1
1
I
t
1
120-mm, M-1943 \ MO
S-60 (57-mm) AA
LT 8,000
1
160-mm, M-160 ! MO
N-5
FM 34-81-1
Table N-3. Weather effects from reduced surface wind.
WEATHER
VALUE
(KNOTS)
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT 1 REMARKS
SYSTEM/EVENT ! REMARKS
NO CRITICAL VALUES !
IDENTIFIED 1
SEE INTRODUCTORY !
PARAGRAPH j
N-6
FM 34-81-1
Table N-4. Weather effects from temperature.
WEATHER
VALUE
(F/C)
SEVERE DEGRADATION
MODERATE DEGRADATION
SYSTEM/EVENT 1 REMARKS
SYSTEM/EVENT 1 REMARKS
NO CRITICAL VALUES I
IDENTIFIED 1
N-7
FM 34-81-1
Table IM-5. Weather effects from precipitation.
WEATHER
CONDITION
Light rain
Moderate
rain
Heavy
rain
SEVERE DEGRADATION
SYSTEM/EVENT
REMARKS
ALSO SEE
INTRODUCTORY
PARAGRAPH
NOTE: The list of air
defense radars on this page
should be considered as a
representative sample of
the various other types of
threat radars associated
with EW operations and
tactical and strategic SAM
systenns.
Not listed are a large
variety of threat combat
equipment (wheeled and
tracked) affected by
moderate or heavy rain and
snow.
MODERATE DEGRADATION
SYSTEM/EVENT
REMARKS
LOW BLOW (fire control)
STRAIGHT FLUSH (12 gHz)
(Tracking)
THIN SKIN (Height finder)
j SAM
! radar
1 SAM
I radar
I SAM
I radar
STRAIGHT FLUSH
(Acquisition)
SAM
radar
LOW BLOW (Fire control)
THIN SKIN (Height finder)
j SAM
I radar
I SAM
j radar
I
N-8
FM 34-81-1
PART II
COMPARISON OF WEATHER EFFECTS ON
US AND THREAT SYSTEMS
The following tables illust rate how sim ilar capabilities of weapon systems
may be compared. For example, [Figure N-l| shows the T-series tanks' acquisition
capabilities are more limited. Obviously, the advantage lies with the friendly tanks.
Under similar weather conditions, the M-1 and M-60 tanks can acquire targets up
to 3000 meters.
Figure N-2 shows similar visibility comparisons of friendly and threat anti-
tank guided missile systems.
N-9
FM 34-81-1
S5
>
LU ^
gi
o
O
o
o
CO
s
CD
CO
o
§
O
GO
C\J
<Q
CO
1 1 ! !
1 1 i i 1 i i i
1111(1111
j 1 1 .! ( t.. I <. i
1 1 1 1 i 1 1 1 1
1 1 1 1 1 1 1 1 t
1 1 1 I J 1 1 1
1 I 1 1 1 1 ! 1
III
i i 1 i i
1 1 1 t 1
I 1 1 1 1
II 1 !
f 1 1 )
( 1 1 1 1 1 1 1
1 1 i i i i i
1 1 1 1 1 1 1
1 1 1 1 1 1 1
!! 1 1 1 1 1 1
1 1 1 1 1 1 1 t
1 1
1 1
1 1
1 1
1 i
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
1 r 1 1 1 1 1 j 1 II
1 1 1 1 t 1 1 1 1 11
1 1 1 i 1 1 i i i 1 i
1 1 1 1 1 1 1 1 1 II
1 1 1 1 i 1 1 1 1 II
1 1 1 .1 ( I I I .. [ 1 1
1 1 1 1 1 t 1 1 1 1
1 1 1 1 I t 1 1 1 1
1 1 1 1 1 t 1 1 1 1
1 ! ! 1 i 1 1 1 1 1
1 1 1 1 ^ t 1 1 1 1
1 1 1 1 1 1 1 1 1 1
1 1 1
^^^^^^^^^^^^^^^^^^^^^^^^^S
1 1 1 1 1
J 1 ! 1 1 1 1 1
1 ; 1 ! 1 1 I 1
1 1 1 1 1 1 ) 1
1 « 1 1 1 J I 1
i
i 1
i 1 i 1 1 i r 1
1 1 1 1 t J 1 i
1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1
I 1 1 1 1 1 1 1
1 1 1 1 1
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
i i 1 i I ! 1 i
1 1 1 1 1 1 1 1
1 1 1 1- L- I I 1
1 1 1 { 1 1 1 1
I 1 f ! ! 1 ! I
1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1
( 1 1 f J 1 1 1
1 ! ! ^ ! 1 ! I
1 1 1 1 1
^^^^^^^^^^^^^^^^^^^^B
1 1 1 f 1
1 1 1 ; 1
1 1 1 1 1
1 ( ( 1 1
i i i i i
_..J i 1 1 1 -. -,
1 1 1 1 J I 1 t t 1 1 t 1 t
! 1 1 1 ) < 1 t 1 1 ( ) 1 t
( 1 1 1 ( 1 < 1 1 1 1 I 1 1
1 1 1 1 1 t 1 » 1 1 1 1 J 1
1 1 1 1 1 1 1 t 1 1 1 S 1 1
1 1 1 1 1 1 i 1 1 1 1 ! 1 1
1 1 1 1 1 i i i 1 i i « 1 i
1 1 1 1 1 i 1 t ^ 1 I S 1 1
1 i 1 1 1 1 1 I 1 i 1
j 1 1 1 ^ ] i i 1 i i i
o
o
o
o
o
o
o
o
o
to
o
o
o
csT
T-54, T-55, T-62
T-64, T-72, T-80
M-1
M-60
o
o
o
Figure N-1. Comparison of US and threat tanks.
N-10
FM 34-81-1
>
LU LL
CO
CD
8
1
o
s
a>
<D
CO
CD
o
CO
in
CD"
o
00
CO"
o
o
o
CD"
o
o
o
o
o
o
o
o
o
CO"
o
o
o
cnI
o
o
o
AT-4 (SPIGOT)
AT-1 (SNAPPER)
AT-3 (SAGGER)
AT-2 (SWATTER)
AT-5 (SPANDREL)&
AT-8 (SONGSTER)
AT-6 (SPIRAL)
TOW
DRAGON
VIPER
LAW
Figure N-2. Comparison between US and threat
anti-tank guided missiles.
N-11
FM 34-81-1
APPENDIX O
WEATHER AND ENVIRONMENTAL ELEMENTS AND PARAMETERS
IMPACTING ARMY SYSTEMS AND OPERATIONS
The data elements and parameters listed in this appendix are from a study
conducted by the US Army Intelligence School as part of the lEW Mission Area
Analysis (lEWMAA). Each TRADOC branch was asked to survey the impact of
weather and environmental elements on their operations, systems, and personnel.
They ranked these impacts as either essential (E) or desired (D). Other Army
agencies also submitted their weather data element requirements which are
incorporated here.
To be listed as E, some positive action had to be taken by the user based on
severe current or forecasted weather conditions. Weather conditions, elements, or
parameters listed as D were identified as having some impact, but the degree of
impact is uncertain or not mission-threatening.
Note that for each element or parameter listed, at least one responder identified
it as essential for one or more of their operations, systems, or personnel.
Some data elements and parameters are known to have an impact, but exact
critical thresholds have not been determined. Others cannot be measured or
sensed with present technology. But identifying these data elements or
parameters now allows for further research in how to collect the raw data (where
applicable), determine the frequency of collection, establish data accuracy, and
learn other supporting information.
Just prior to this printing, 10 of the 24 agencies stating requirements submitted
updates to their original needs. Ninety two new essential requirements and 22
new desired requirements were added. Additionally, 9 desired requirements were
upgraded to essential, and 11 essential requirements were downgraded to
desirable. Four existing requirements were deleted.
These updated data requirements are reflected in [Figure 0-l| . As users and
planners continue to learn more about weather and environmental impacts, the
misconception there is such a hypothetical thing as an Army "all-weather" system
or operation fades. New values and impacts will be added to this manual as the
information becomes available.
O-l
FM 34-81-1
WEATHER AND ENVIRONMENTAL
DATA ELEPvlENTS IMPACTING ARMY SYSTEMS/OPERATIONS
A - AIR DEFENSE t - FINANCE Q = ORDNANCE M&M
B = ADJUTANT GENERAL J = HEALTH SERVICES R = PUBLIC AFFAIRS
C = ARMOR K = INTELLIGENCE S = QUARTERMASTER
D ^ AVIATION L = INFANTRY T = SIGNAL
E = CHAPLAIN M = JUDGE ADVOCATE U = SPECIAL FORCES
F = DEFENSE AMMUNITION CENTER N - MILITARY POLICE V = SOLDIER SUPPORT
II G = ENGINEER = CHEMICAL W = TRANSPORTATION
H = FIELD ARTILLERY P - ORDNANCE X = JOINT READINESS TRNG CENTER
REQUIREMENT DESIGNATORS: E = ESSENTIAL SUPPORT NEEDS D = DESIRABLE SUPPORT NEEDS
SPECIAL GROUP CATEGORIES: [GS] = GROUND STATE [SS] = SEA STATE ISW] = SEVERE WEATHER CRITERIA
DATA ELEMENT CATEGORY
A
B
■9^'
D
E
F
Q
H
1
J
.*:
L
M
N
O
p
^■\
R
■;si-
T
■;^:
V
m
X
1. ALTIMETER SETTING
E
E
\^,'
m:
':■ '■:■ :
2. ATMOSPHERIC CONTAMINANTS
E
D
D
E
D
E
E
.,: .
D
im^
x>
;ix>-^
3. ATMOSPHERIC DENSITY
E
E
t'
4. ATMOS. TRAMSMiSSION COEFFICIENT
E
0.^-;
_
'■ w ■
■ . -:■' :
5. BAROMETRIC PRESSURE
D
t
E
E
E
E
■■:!;■:
'■' >: '■:
:fe;:
e
6. CLOUD COVER AMOUNT
b
■E-
E
E
E
E
E
E
E
D
■£■
D
E
:.|E
e
7. CLOUD BASE HEIGHT
E
E
E
E
E
E
■■^E-
E
D
E
E
£
e
8. CLOUD TOP HEIGHT
E
E
E
:pi
9. DAMAGING WINDS [SW]
e
E
£
E
E
D
E
E
E
E
E
E
f
E
E
D
:.£■
E
;r
E
E
E
■;*:
E
10. DENSITY ALTITUDE
E
E
E
::E-
:■:':■: ':
e
11. EXTINCTION COEFFICIENT
E
E
:''-■■
P
:;--■■;:::
1 2, EXTREME HEAT/COLD [SWl
E
E
E
E
E
E
E
E
£
E
E
E
£
E
■■■^
D
■El
E
;:£
E
i-E
E
£
E
13, FLOODING. RtVER STAGE [GSl
E
E
E
E
E
E
D
E
E
E
E
E
E
E
D
e
E
M
E
■E
E
E
E
14. FREEZE/THAW DEPTH [GS]
D
E
E
E
D
E
E
E
E
P
E
E
"M
E
E
15. FREEZING PRECIPITATION [SWj
E
E
E
E
E
E
E
E
E
E
E
£
E
E
D
E
E
£
E
£
E
E
E
16. HEAVY RA!N/SNOVy [SW]
E
E
E
E
E
D
E
E
E
E
E
E
e
E
E
E
D
E
■£■
E
■;e
E
M
E
17. HUMIDITY, ABSOLUTE
D
E
E
E
e
-.£■
::■■:;:■
^■E.
'■-•:■•■■
E
18. HUMIDITY, ABSOLUTE, PROFILE
D
E
E
E
E
E
:■:;>■
■£■
?>
E
19. HUMIDITY, RELATIVE
E
E
D
E
E
E
£
p
E
■E;
E
20. HUMIDITY, RELATIVE. PROFILE
E
■'■■-:
p
;;;.■:
21 . HURRICANES/TYPHOONS ISWt
E
E
£
E
E
E
E
E
E
E
E
E
E
E
D
E
E
\t
E
£
E
■£■
E
22. ICE/SNOW DEPTH/COVER [GSi
D
E
E
E
D
E
E
E
E
P
D
E
■M
E
P
■:■ :■:
E
23. ICING, FLIGHT ISW|
_
E
E
E
E
;-: ■
::E^
E
24. ILLUMINATION
e
E
E
E
E
E
E
E
E
D
b
E
£
E
E
^5. !R TARGET/BACKGROUND CONTRAST
E
E
D
E
D
■:-. '-.
■£•
E
26. IR THERMAL CONTRAST X-OVER TIME
E
E
D
E
E
.:: ■:
i::l
E:-
;;■ y
E
27. IONOSPHERIC DISTURBANCES
■
D
D
E
■::
*i-:i;i
E
E
28. LIGHT DATA
E
E
E
D
E
D
E
E
E
D
b
b
D
E
P
D
23. LIGHTNINGm HUNDERSTORMS [SVv'i
D
E
E
E
D
E
;i
.£:;
■i: :■
E
30. LITTORAL CURRENT [SS]
D
D
E
D
b
E
%
31. PRECIPITATION, ACCUMULATION
D
E
E
D
D
E
D
D
E
E
E
E
D
E
D
ji
E
£
E
;:e;
D
Figure 0-1. Weather and environmental data elements Impacting
Army systems and operations.
0-2
FM 34-81-1
DATA ELEMENT CATEGORY
A
B
c
D
E
F
GJH
1
J
k
L
fj\
N
P
q|r
s
T
i'W
V
w
\^
32. PRECIPITATION, RATE
£
D
1 ^t'l 1
E
D
E
E
D
E
£
E
D
E
E
D
: --■:•■
D
■£-.
£
E
T
T
E
33. PRECIPITATION, HAIL SIZE
£
■■:
E
..
E
D
■ :-,
E
E
E
:.'.;
E
't.
P
■•:=::;
34. PRECIPITATION, TYPE
£
D
E
E
D
E
E
E
E
E
D
E
E
D
D
E
E
6
E
t
E
35. PRESSURE ALTITUDE
.
E
E
E
E
E;
>'■'■'■
E
36. REFRACTIVE INDEX
£
£
E
D
■ ,]'
E
E
D
_ . ■;
■■;■■
•';.;
. :■■ :
:t:
37. RESTRICTION TO VISIBILITY
E
E
D
D
E:
E
E
■■:
£
E
e
:;. :'
E
38. SEE ABILITY (millimeter wave, infrarfo. ultraviolet}
E
t
E
E
E
E
E
E
E
V
■ .'■■
E
E.
D
39. SEVERE WEATHER CONDiTlONS iSWl
£
E
£
E
£
E
E
E
E
E
£
E
E
;E
D
■:£:
E
■E
E
^E
E
E-
El
40. SNOW STATE CONDITION IGS!
D
e:
E
E
E
E
E
E
E
P
D
:£
Ej
£
D
i]
41 . SNOW DRIFT DEPTH [GSl
D
D
:■£■
D
D
E
E
E
;■ ■
E
.:■;
E
E
:•■■ ••■
il
42. SOIL/GROUND MOISTURE [GS]
D
E
E
D
£
D
E
E
£
£
D
E
D
£
D
'-A
£
43. SOIL/GROUND TEMPERATURE |GS1
£
E
D
E
D
E
E
E
E
E
:•' :'
D
D
E
E
E
E
44. SOLAR RADIATION
E
D
:,
: : :■
:e
45. STABILITY INDEX
■■■
E
E
■£:;
rr
;:-:
i]
46. STANDING WATER/POOLING [GS]
£
E
D
■£.
D
E
E
E
E
D
D
;£•
D
:e'
£
P
E
47. STATIC ELECTRICITY POTENTIAL
E
E
E
:■ ■
48. SURF HEIGHT iSS]
D
e,
D
E
!:■>
E
E
49. SWELL DIRECTION/HEIGHT ISSj
D
D
E
-:'■
E
*****
50. TEMPERATURE, AIR, SURFACE
E
E
E
E
£
E
E
E
E
E
E
E
£
E
D
E
P
£
E
£
E
£
51. TEMPERATURE, AIR, PROFILE
E
E
E
E
E
iO^
: .■ ■
52. TEMPERATURE, AIR. UPPER AIR
E
E
E
E;
:•• ■
P
El
53. TEMPERATURE, DEWPOINT
£
E
D
E
E
:■.■:
£
e\
54. TEMPERATURE, DEWPOINT, PROFILE
E
E
E
£
■ "•: -.
P
. :.- ■'.
55. TEMPERATURE. WINDCHILL FACTOR
D
D
E
D
D
E
E
E
P
E
£
D
£
E
E
:EJ
56. TEMPERATURE. INVERSION LEVEL(S)
E
E
E
£
£
:e|
'■'. ■■
:■■ ■
D
£
57. TEMPERATURE, SEA SURFACE ISS]
D
E
D
p
E
■ ::
E
B
58. TEMPERATURE, WATER, INLAND [GS|
D
E
D
E
…[truncated]