Mountain Terrain, Weather, and Hazards

short time or with a minor shift in locality. The severity and variance of the weather causes it to have a
major impact on military operations.

CONSIDERATIONS FOR PLANNING
1-44. Mountain weather can be either a dangerous obstacle to operations or a valuable aid, depending on
how well it is understood and to what extent advantage is taken of its peculiar characteristics.

Weather often determines the success or failure of a mission since it is highly changeable.
Military operations plans must be flexible, especially in planning airmobile and airborne
operations. The weather must be anticipated to allow enough time for planning so that the
leaders of subordinate units can use their initiative in turning an important weather factor in their
favor. The clouds that often cover the tops of mountains and the fogs that cover valleys are an
excellent means of concealing movements that normally are made during darkness or in smoke.
Limited visibility can be used as a combat multiplier.

The safety or danger of almost all high mountain regions, especially in winter, depends upon a
change of a few degrees of temperature above or below the freezing point. Ease and speed of
travel depend mainly on the weather. Terrain that can be crossed swiftly and safely one day may
become impassable or highly dangerous the next due to snowfall, rainfall, or a rise in
temperature. The reverse can happen just as quickly. The prevalence of avalanches depends on
terrain, snow conditions, and weather factors.

Some mountains, such as those found in desert regions, are dry and barren, with temperatures
ranging from extreme heat in the summer to extreme cold in the winter. In tropical regions, lush
jungles with heavy seasonal rains and little temperature variation often cover mountains. High
rocky crags with glaciated peaks can be found in mountain ranges at most latitudes along the
western portion of the Americas and Asia.

Severe weather may decrease morale and increase basic survival problems. These problems can
be minimized when men have been trained to accept the weather by being self-sufficient.
Mountain Soldiers properly equipped and trained can use the weather to their advantage in
combat operations.

MOUNTAIN AIR
1-45. High mountain air is dry and may be drier in the winter. Cold air has a reduced capacity to hold
water vapor. Because of this increased dryness, equipment does not rust as quickly and organic material
decomposes slowly. The dry air also requires Soldiers to increase consumption of water. The reduced water
vapor in the air causes an increase in evaporation of moisture from the skin and in loss of water through
transpiration in the respiratory system. Due to the cold, most Soldiers do not naturally consume the quantity
of fluids they would at higher temperatures and must be encouraged to consciously increase their fluid
intake.

Pressure is low in mountainous areas due to the altitude. The barometer usually drops 2.5
centimeters for every 300 meters gained in elevation (3 percent).

The air at higher altitudes is thinner as atmospheric pressure drops with the increasing altitude.
The altitude has a natural filtering effect on the sun’s rays. Rays are absorbed or reflected in part
by the molecular content of the atmosphere. This effect is greater at lower altitudes. At higher
altitudes, the thinner, drier air has a reduced molecular content and, consequently, a reduced
filtering effect on the sun’s rays. The intensity of both visible and ultraviolet rays is greater with
increased altitude. These conditions increase the chance of sunburn, especially when combined
with a snow cover that reflects the rays upward.

WEATHER CHARACTERISTICS
1-46. The earth is surrounded by an atmosphere that is divided into several layers. The world’s weather
systems are in the lower of these layers known as the troposphere. This layer reaches as high as 40,000
feet. Weather is a result of an atmosphere, oceans, land masses, unequal heating and cooling from the sun,
and the earth’s rotation. The weather found in any one place depends on many things such as the air

26 July 2012

TC 3-97.61

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