What is the Wind Chill formula?
Wednesday, July 24, 2013, 11:17 AM - The wind chill formula was changed because it was not reflective of what was happening at ground level. The previous formula was giving too cold of a wind chill value. The revised formula places more emphasizes on the current temperature to obtain the wind chill value. The wind measurement is taken at 10 metres above the ground.
The new formula takes into account an assumed friction of 1.52 metres (5-6 feet) above the ground and uses a model of a human face, incorporates modern heat transfer theory (heat loss from the body on cold and breezy/windy days), reduces the calm wind threshold to 4.827 km/h, uses a consistent standard for skin tissue resistance and assumes the worst case scenario for solar radiation, for example a clear night sky. The new calculation is:
WCT = 13.12 + 0.6215 x Tair - 11.37 x V10metre0.16 +0.3965 x Tair x V10metre0.16
Tair - is the surface temp in C
V10metre - is the standard surface wind speed in km/hr
The WCT Chart with these calculations is attached immediately below:
Forecast-your-own Wind Chill
If you know the temperature outside, you can estimate the wind speed by observing the movement of trees and flags, and then find the wind chill on the second chart.
|Wind Speed||What to look for|
|10 km/h||Wind felt on face; leaves rustle; wind vanes begin to move.|
|20 km/h||Leaves & small twigs constantly moving; small flags extended.|
|30 km/h||Dust, leaves, & loose paper lifted; large flags flap; small tree branches move.|
|40 km/h||Small trees begin to sway; large flags extend and flap.|
|50 km/h||Larger tree branches moving; whistling heard in power lines; large flags extend and flap more wildly.|
|60 km/h||Whole trees moving; resistance felt in walking against wind; large flags extend fully and flap only at the end.|