Wind Chill Calculator

What is wind chill?

Wind chill describes how cold it feels on exposed skin when wind is added to low temperatures. The body warms a thin layer of air next to the skin; wind strips that layer away and replaces it with colder air, so heat is lost faster and skin cools as if the air were colder than it is.

Wind chill does not change the actual temperature, and it affects only things that are warmer than the air. A car radiator or a water pipe will not freeze unless the air itself is below freezing, no matter how strong the wind; the wind simply makes them cool down to air temperature faster. For people and animals, though, faster heat loss means a greater risk of frostbite and hypothermia.

How to calculate wind chill

The current Wind Chill Temperature index was introduced by the US National Weather Service and Environment Canada in 2001. It is based on a model of heat loss from a human face walking at about 3 mph into the wind on a clear night, and was validated with volunteers in a chilled wind tunnel. It replaced the older Siple-Passel index from the 1940s, which overstated the chill. At 10 °F with a 15 mph wind, the default example, it feels like about −7 °F.

WCT = 35.74 + 0.6215T − 35.75V^0.16 + 0.4275TV^0.16

WCT

wind chill temperature in °F

T

air temperature in °F (50 °F or below)

V

wind speed in mph at 33 ft (10 m), 3 mph or above

Metric form: WCT = 13.12 + 0.6215T − 11.37V^0.16 + 0.3965TV^0.16, with T in °C and V in km/h.

Frostbite

Frostbite is the freezing of skin and the tissues beneath it. It most often affects the fingers, toes, nose, ears, cheeks and chin. In the earliest stage, frostnip, skin turns red and stings, then goes numb; it recovers fully with warming. In deeper frostbite the skin turns white or grayish-yellow, feels unusually firm or waxy, and may blister after rewarming. Severe frostbite can destroy tissue permanently and lead to amputation.

Risk climbs quickly as wind chill drops. The National Weather Service estimates that exposed skin can freeze in about 30 minutes at a wind chill around −18 °F (−28 °C), and in 10 minutes or less at much lower values. Wet skin, tight clothing, smoking, alcohol, diabetes and poor circulation all increase the risk.

If you suspect frostbite, get into a warm place, remove wet clothing, and warm the area gently in warm (not hot) water or with body heat. Do not rub the skin or use heating pads or fires, because numb skin burns easily, and do not rewarm if there is a chance it will refreeze. Seek medical care for anything beyond mild frostnip.

Hypothermia

Hypothermia occurs when the body loses heat faster than it can produce it and the core temperature falls below 95 °F (35 °C). Early signs are shivering, fumbling hands, slurred speech, confusion and drowsiness, sometimes called the umbles: stumbles, mumbles, fumbles and grumbles. As it worsens, shivering stops, breathing and pulse slow, and the person may lose consciousness.

Older adults, infants, people who are outdoors for long periods, and anyone who is wet, exhausted or has been drinking are most at risk. Call emergency services, move the person somewhere warm, remove wet clothing and warm the center of the body first with dry layers and blankets. Hypothermia is a medical emergency.

Dress Warmly for Winter

Several loose layers trap warm air better than one thick garment, and let you shed a layer before you start to sweat; damp clothing loses much of its insulation. Cover the head, face and ears, wear mittens rather than gloves in severe cold, and keep feet dry with wool or synthetic socks and insulated, waterproof boots. Check the forecast, limit time outdoors when wind chill warnings are issued, and tell someone your plans.

Frequently asked questions

Sources

• National Weather Service – Wind Chill
• CDC – Winter weather: frostbite and hypothermia