The Wind Chill Factor When Traveling

Staying in comfort when traveling by understanding the wind chill factor

As we all know, wind, temperature and humidity have a bearing on our comfort. To indicate how combinations of these elements affect the weather we experience, two indices should be understood: wind chill factor and temperature/humidity comfort index.

The Wind Chill Factor

The wind chill factor is the cooking effect on the body of any combination of wind and temperature. It accounts for the rate at which our exposed skin loses heat under differing wind-temperature conditions. In a wind of 32 kph, -4°C will feel like -19°C. This effect is called "wind chill", the measure of cold one feels regardless of the temperature. Chill increases as the temperature drops and winds get stronger - up to about 72 kph, beyond which there is little increase. Thus at 12°C, increasing the wind from 0 to 8 kph reduces temperature by only two degrees, but a change in wind speed from 64 to 72 kph reduces it only 0.5°C.

The wind may not always be caused naturally. For example, someone skiing into the wind may receive quite a chill. If one is moving into the wind, the speed of travel is added to the wind speed; thus if the wind is blowing at 16 kph and one's speed is 24 kph into the wind, the actual air movement against the body is 40 kph. At -9°C this air speed gives a wind chill equivalent to -30°C. This is easily cold enough for exposed parts of the body to sustain frostbite.

A combination of warm temperatures and humidity also has a significant bearing on our comfort, particularly in warmer climates when the higher the relative humidity, the less comfortable we are. This is a result of the corresponding decrease in the rate at which moisture can evaporate from the skin's surface. Since the cooling of the air next to the skin by the evaporation of perspiration is what causes a cooling sensation, a day with 70 per cent relative humidity and 27°C temperature is far less comfortable than one with 25 per cent humidity and 43°C temperature. The THI was developed in order to measure this relative comfort. But remember, where there is low humidity and a high temperature, your comfort can mislead you, for though you feel safe, you may be in danger of burning.