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Wind Chill
The NWS implemented a replacement Wind Chill Temperature (WCT) Index during the 2001/2002 Winter Season. The reason for this change was to improve upon the old WCT Index used by the NWS and the Meteorological Services of Canada, which was based on the 1945 Siple and Passel Index.
| Wind Chill is the term used to describe the rate of heat loss from the human body resulting from the combined effect of low temperature and wind. As winds increase, heat is carried away from the body at a faster rate, driving down both the skin temperature and eventually the internal body temperature. |
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The Wind Chill Index is designed for heat loss in humans. It has no effect on inanimate objects.
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Wind Chill, the measure of the rate of heat loss based on air temperature and wind speed, is not a true temperature, but it allows us to understand how heat is lost to the wind.
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The old WCT formula was introduced by Antarctic explorer Paul A. Siple in his 1939 dissertation, "Adaptation of the Explorer to the Climate of Antarctica." During the 1940s, Siple (who coined the term "wind chill") and Charles F. Passel experimented with measuring the time it took to freeze 250 grams of water in different temperature and wind conditions. They developed empirical formulas relating that data to the rate of heat loss from exposed human skin.
The new WCT formula makes use of advances in science, technology and computer modeling to provide a more accurate, understandable and useful formula for calculating the dangers from winter winds and freezing temperatures. In addition, clinical trials have been conducted and the results of those trials have been used to verify and improve the accuracy of the new formula.
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Specifically, the WCT Index:
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Uses wind speed calculated at the average height (5 feet) of the human face, instead of 33 feet (the standard anemometer height),
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Is based on a human face model,
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Incorporates modern heat transfer theory,
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Lowers the calm wind threshold to < 3 mph,
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Uses a consistent standard for skin tissue resistance,
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Assumes the worst case scenario for solar radiation (clear night sky).
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New Wind Chill Chart
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Temperature (° F)
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Wind Speed
(mph) |
calm |
40 |
35 |
30 |
25 |
20 |
15 |
10 |
5 |
0 |
-5 |
-10 |
-15 |
-20 |
-25 |
| 5 |
36 |
31 |
25 |
19 |
13 |
7 |
1 |
-5 |
-11 |
-16 |
-22 |
-28 |
-34 |
-40 |
| 10 |
34 |
27 |
21 |
15 |
9 |
3 |
-4 |
-10 |
-16 |
-22 |
-28 |
-35 |
-41 |
-47 |
| 15 |
32 |
25 |
19 |
13 |
6 |
0 |
-7 |
-13 |
-19 |
-26 |
-32 |
-39 |
-45 |
-51 |
| 20 |
30 |
24 |
17 |
11 |
4 |
-2 |
-9 |
-15 |
-22 |
-29 |
-35 |
-42 |
-48 |
-55 |
| 25 |
29 |
23 |
16 |
9 |
3 |
-4 |
-11 |
-17 |
-24 |
-31 |
-37 |
-44 |
-51 |
-58 |
| 30 |
28 |
22 |
15 |
8 |
1 |
-5 |
-12 |
-19 |
-26 |
-33 |
-39 |
-46 |
-53 |
-60 |
| 35 |
28 |
21 |
14 |
7 |
0 |
-7 |
-14 |
-21 |
-27 |
-34 |
-41 |
-48 |
-55 |
-62 |
| 40 |
27 |
20 |
13 |
6 |
-1 |
-8 |
-15 |
-22 |
-29 |
-36 |
-43 |
-50 |
-57 |
-64 |
| 45 |
26 |
19 |
12 |
5 |
-2 |
-9 |
-16 |
-23 |
-30 |
-37 |
-44 |
-51 |
-58 |
-65 |
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"Calm-air" as used in wind chill determinations actually refers to the conditions created by a person walking briskly (at 4 miles-per-hour) under calm wind conditions.
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Frostbite Time for Exposed Skin (minutes)
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30 |
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15 |
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10 |
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5 |
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Wind Chill Formula: **
| WCT (°F) = 35.74 + 0.6215T - 35.75(V 0.16) + 0.4275T(V 0.16) |
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where, T = Air Temperature (° F), V = Wind Speed (mph)
(** - valid only for wind speeds > 4 mph)
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Exposure to cold can cause frostbite or hypothermia, and become life-threatening. Infants and elderly people are most susceptible.
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Frostbite is damage to body tissue caused by extreme cold. A wind chill of -20° F will cause frostbite in just 30 minutes. Frostbite causes a loss of feeling and a white or pale appearance in extremities, such as finger, toes, earlobes, or the tip of the nose. If symptoms are detected, get medical help immediately! If you must wait for help, slowly rewarm the affected areas. However, if the person is also showing signs of hypothermia, warm the body core before the extremities.
Hypothermia is a condition brought on when the body core temperature drops to less than 95
° F. It can kill. For those who survive, there are likely to be lasting kidney, liver, and pancreas problems. Warning signs include uncontrollable shivering, memory loss, disorientation, incoherence, slurred speech, drowsiness, and apparent exhaustion.
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If Medical Care is Not Available, warm the person slowly, starting with the body core. Warming the arms and legs first drives cold blood toward the heart, and can lead to heart failure. If necessary, use your body heat to help. Get the person in to dry clothing and wrap them in a warm blanket, covering the head and neck. Do NOT immediately give the person alcohol, drugs, coffee, or any hot beverage or food. Once the body core temperatures warms back to normal, warm broth is the first food to offer.
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