When assessing weather conditions for troops operating in mountainous regions or for flight personnel in aircraft, altitude may need to be considered, if weather measurements are obtained from stations at low elevations. Temperatures, windchills and the risk of cold injury at high altitudes can differ considerably from those at low elevations. In general, it can be assumed that air temperature is 3.6 o F lower with every 1000 feet above the site at which temperature was measured. Winds are usually more severe at high altitude, and there is less cover above the tree line. Individuals are more susceptible to frostbite and other cold injuries at altitudes above 8,000 feet than at sea level, due to the lower temperatures, higher winds, and lack of oxygen.
Water can conduct heat away from the body much faster than air of the same temperature.
When clothing becomes wet due to snow, rain, splashing water, or accumulated sweat, the body's loss of heat accelerates. For example, when air temperature is 40 o F, heat loss in wet clothing is double what it is in dry clothing. Swimmers and persons working or wading in water can lose a great deal of body heat even when water temperatures are only mildly cool. Individuals working in cold water should be closely watched while they enter the water, since sudden plunging into cold water can produce irregular heart beats, gasping, and hyperventilation, which could cause inhalation of water, heart failure, and drowning. Metal objects and liquid fuels that have been left outdoors in the cold can pose a serious hazard.