Content-Length: 9728 | pFad | http://weather.uky.edu/aen599/wchart.htm
(Wind Chill Equivalent Temperature)
Wind chill is based on the rate of heat loss from exposed skin caused by combined effects of wind and cold. As the wind increases, heat is carried away from the body at an accelerated rate, driving down the body temperature.
(MPH) 35 30 25 20 15 10 5 0 -5 -10 -15 -20 -25 -30
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5: 32 27 22 16 11 6 0 -5 -10 -15 -21 -26 -31 -36
10: 22 16 10 3 -3 -9 -15 -22 -27 -34 -40 -46 -52 -58
15: 16 9 2 -5 -11 -18 -25 -31 -38 -45 -51 -58 -65 -72
20: 12 4 -3 -10 -17 -24 -31 -39 -46 -53 -60 -67 -74 -81
25: 8 1 -7 -15 -22 -29 -36 -44 -51 -59 -66 -74 -81 -88
30: 6 -2 -10 -18 -25 -33 -41 -49 -56 -64 -71 -79 -86 -93
35: 4 -4 -12 -20 -27 -35 -43 -52 -58 -67 -74 -82 -89 -97
40: 3 -5 -13 -21 -29 -37 -45 -53 -60 -69 -76 -84 -92 -100
15°F to 30°F COLD. Unpleasant.
0°F to 15°F VERY COLD. Very unpleasant.
-20°F to 0°F BITTER COLD. Frostbite possible.
-20°F to -60°F EXTREMELY COLD. Frostbite likely. Outdoor activity becomes dangerous.
* Wind speeds greater than 40 MPH have little additional cooling effect.
Wind chill factor (equivalent temperatures) can also be useful in determining the influence of weather on livestock. The response of livestock to cold varies considerably, depending upon the species, breed, condition, and the ration being fed. In general, lower temperatures increase the amount of feed required to maintain a given production level. The animal may sense that the weather is colder either by a drop in the air temperature or an increase in wind speed.
When determining air temperature with a typical thermometer, the location and exposure of the device generally has much more effect on accuracy than the inherent instrument error. For proper measurement of air temperature with a thermometer, it should be sheltered from precipitation and direct sunlight but be open to free air movement. If you have no instrument to measure wind speed, the Table below can be useful in making an estimate.-------------- ---------------------------------------------
Less than 1 Calm. Smoke rises vertically.
1 - 3 Direction of wind shown by smoke drift, not by
wind vanes.
4 - 7 Wind felt on face; leaves rustle; ordinary vane
moved by wind.
8 - 12 Leaves and small twigs in constant motion; wind
extends light flag.
13 - 18 Raises dust and loose paper; small branches are
moved.
19 - 24 Small trees in leaf begin to sway; crested wavelets
form in inland waters.
25 - 31 Large branches in motion; whistling heard in
telephone wires; umbrellas used with dificulty.
32 - 38 Whole trees in motion; inconvenience felt in
walking against wind.
WIND CHILL FORMULA(S):
If you have units of wind in mph and temp in degrees F...try
this:
T(wc) = 0.0817(3.71V**0.5 + 5.81 -0.25V)(T - 91.4) + 91.4
T(wc) is the wind chill, V is in the wind speed in statute miles per
hour and T is the temperature in degrees Fahrenheit.
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Here's another formula with temp in Kelvin and wind in meters per sec.
Wind Chill T (in K) = 306.15 - (0.453843 * SQRT(Speed) + 0.464255
- 0.0453843 * Speed) * (306.15 - Temp [in K])
As you can see it is a bit complicated but this is the "official" NWS
formula. I hope I typed it out correctly!
Note: Speed (above) is in meters per second and Temps are in degrees Kelvin.
Developed by Siple and Passel (1945):
H = (SQRT(100V) + 10.45 - V) x (33 - T)
where H = windchill in kilocalories per square metre of exposed flesh
per hour
V = wind speed in metres per second and T = air temperature in degrees C
For more information concerning wind chill, contact your local county
extension agent or Tom Priddy in the UK Ag Weather Center.
Fetched URL: http://weather.uky.edu/aen599/wchart.htm
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