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Outdoor Article of the Month - February 1997
Windchill
Outdoor Article of the Month - February 1997
Windchill
During cold weather our bodies lose heat through five major mechanisms: Conduction, Convection, Radiation, Evaporation and Respiration. Conduction is when you lose heat touching something colder than you are. Convection is simply the wind blowing away the layer of warm air that is normally next to your skin. Radiation is the process by which your body radiates heat. Evaporation translates to losing heat when water (such as perspiration) changes phase from liquid to gas. Respiration is breathing and breathing in cold air cools your core. Convection and evaporation together can rapidly strip heat away from your body. The windchill equivalent temperature is simply a way or relating how wind appears to make a given temperature cool things as though it were really much colder.
Windchill Equivalent Temperature
km/h
mph
0
-5
-10
-15
-20
-25
-30
-35
10
6
-2
-7
-12
-17
-22
-27
-32
-38
20
12
-7
-13
-19
-25
-31
-37
-43
-50
30
18
-11
-17
-24
-31
-37
-44
-50
-57
40
24
-13
-20
-27
-34
-41
-48
-55
-62
50
30
-15
-22
-29
-36
-44
-51
-58
-66
60
36
-16
-23
-31
-38
-45
-53
-60
-68
Windchill Factor (in Watts per Square Meter)
0
-5
-10
-15
-20
-25
-30
-35
10
6
933
1075
1216
1358
1499
1641
1782
2009
20
12
1092
1257
1423
1588
1753
1919
2084
2248
30
18
1189
1369
1549
1729
1909
2089
2269
2449
40
24
1253
1443
1633
1823
2013
2202
2393
2583
50
30
1298
1494
1691
1887
2084
2280
2477
2673
60
36
1327
1529
1730
1931
2132
2334
2535
2736
Windchill Factor / (Equivalent Temperature)
Effect of Windchill
Under 900 (-3 C)
Conditions comfortable with normal winter clothing.
900 - 1400 (-18 C)
Conditions no longer pleasant for outdoor activities on overcast days. Work and recreation becomes uncomfortable unless properly clothed. Hats, coats and gloves are recommended.
1400 - 1600 (-25 C)
Conditions no longer pleasant for outdoor activities on sunny days. Outdoor work and travel are safe with quality winter clothing.
1600 - 1800 (-30 C)
Frostbite can occur with prolonged exposure. Heavy outer clothing is essential. Your weather office will add the current wind chill to public forecasts at this level.
1800 - 2000 (-35 C)
Frostbite can occur in a few minutes. Multiple layers of clothing become essential.
2000 or more (-40 C)
Unprotected skin can freeze in one minute. Adequate face protection becomes important. Elementary school children require continuous adult supervision while outdoors. Work and travel alone is not advisable.
2200 or more (-45 C)
Adequate face protection becomes mandatory. Work and travel alone is hazardous. Special warm-up breaks are recommended for outside workers.
2300 or more (-50 C)
Outdoor conditions become dangerous. School closures should be considered. Exposed areas freeze in less than one minute for the average person.
2400 or more (-60 C)
Outdoor conditions are dangerous even for short periods of time. All non- emergency outdoor work should cease. Buddy system and observation are mandatory.
2600 or more (-65 C)
Exposed flesh freezes in less than one half minute on average. These are rare wind chill values which will be experienced in some major blizzards. Danger is extreme.
Other factors can affect comfort and your degree of risk including: age, body type, humidity, clothing, level of physical activity, sunshine and even your food intake.
Rescue Dynamics Copyright © 1997 Cyril Shokoples
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