Fact Sheet: Old Wind Chill


Glen Conner
State Climatologist Emeritus for Kentucky

Wind Chill

• Everyone has noticed that in winter it seems colder when the wind is blowing. Mothers recognize this and tell their children to wear more clothes. The question the children ask is how much more clothes. Mothers answer very precisely because Mothers know everything. For the rest of us, wind chill calculations are the basis for determining the effect of wind on body heat loss.

Siple and Passel Experiments

• In 1941, Paul A.Siple and Charles F. Passel conducted experiments in Antarctica to determine the time required to freeze 250 grams of water exposed to the elements. Their measurements were in kilogram calories per square meter per hour. When plotted against wind speed, they found that it was the combination of wind and temperature that controlled the rate at which heat was lost. They used these heat loss findings to determine heat loss from the exposed skin of humans.

• Later modifications of the equation produced the wind chill equivalent temperature. This is what forecasters and weathercasters give as the wind chill. It means that you would feel as cold at the current temperature and wind speed as you would at the equivalent temperature when wind was not a factor. The four miles per hour speed of brisk walking is used as the wind speed of neutral effect.

Old Wind Chill Equation

• The wind chill equivalent temperature (Ce) equation is:
Ce = 33 - (10.45 + 10(sqrt(V) - V)(33 - C)/ 22.04
where C is the air temperature in Celsius and V is the wind speed in meters per second.

• Using the two charts below, you may now determine the wind chill equivalent temperature whenever you feel the need. Then you will know how much clothing to wear. Or, you can just ask your Mother.


AIR TEMPERATURE (F)
WIND
35
30
25
20
15
10
5
0
-5
-10
-15
-20
-25
-30
-35
MPH
4
35
30
25
20
15
10
5
0
-5
-10
-15
-20
-25
-30
-35
5
32
27
22
16
11
6
0
-5
-10
-15
-21
-26
-31
-36
-42
10
22
16
10
3
-3
-9
-15
-22
-27
-34
-40
-46
-52
-58
-64
15
16
9
2
-5
-11
-18
-25
-31
-38
-45
-51
-58
-65
-72
-78
20
12
4
-3
-10
-17
-24
-31
-39
-46
-53
-60
-67
-74
-81
-88
25
8
1
-7
-15
-22
-29
-36
-44
-51
-59
-66
-74
-81
-88
-96
30
6
-2
-10
-18
-25
-33
-41
-49
-56
-64
-71
-79
-86
-93
-101
35
4
-4
-12
-20
-27
-35
-43
-52
-58
-67
-74
-82
-89
-97
-105
40
3
-5
-13
-21
-29
-37
-45
-53
-60
-69
-76
-84
-92
-100
-107

 

    Estimating Wind Speed
4 - 7
  Wind felt on face, leaves on trees rustle
8 - 12
  Leaves and small twigs constantly move
13 - 17
  Loose paper is lifted, dust is raised
18 - 24
  Small trees sway
25 - 31
  Large branches move, overhead wires whistle
32 - 38
  Whole trees move, inconvenient walking
39 - 46
  Small twigs break, impeded walking
47 - 54
  Large branches and weak limbs break
55 - 63
  Moderate structural or tree damage
64+
   Heavy to severe structural or tree damage


Computing the Old Wind Chill

• When you enter the temperature in Fahrenheit and the wind speed in miles per hour in the form below, the wind chill equivalent temperature will be calculated and displayed for you.


Wind Chill
Temperature F Wind Velocity Wind Chill


References


• Falconer, Raymond. 1968: Windchill, A Useful Wintertime Weather Variable. Weatherwise, 21:6, pp 227-229, 253.

• Siple, Paul A. and Charles F. Passel. 1945: Measurements of Dry Atmospheric Cooling in Subfreezing Temperatures. Proceedings of the American Philosophical Society, 89:1, pp 177-179.

• Wind Chill. 1975: Environmental Information Summaries, C-3, U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Climatic Data Center, Asheville, NC.