Scott, I've included the equations below but I recommend visiting my web
site where I have a variety of meteorological links including standards,
equations, DIY projects, and more:

      http://www.teleport.com/~thandley/Wilbure.htm

   The standard formula for Wind Chill used by the National Weather Service:

      Twc = 0.0817 * (3.71 * sqrt(V) + 5.81 - 0.25 * V) * (T - 91.4) + 91.4

      Where:

         Twc = Wind Chill in degrees Fahrenheit.
         T   = Current temperature in degrees Fahrenheit.
         V   = Wind speed in Statute miles per hour.

   The following is the Dewpoint equation. Note, I broke the equation up
into smaller pieces for convenience. If you already have Tc, ignore the
first line.

      Tc  = (Tf - 32) / 1.8
      a   = (7.5 * Tc) / (237.7 + Tc)
      Pw  = 6.11 * 10^a
      Pwp = Pw * (RH / 100)
      b   = log10(Pwp) - log10(6.11)
      DPc = (237.7 * b) / (7.5 - b)
      DPf = (DPc * 1.8) + 32

      Where:
         RH  = Relative Humidity (%)
         Tf  = Temperature (F)
         Tc  = Temperature (C)
         DPc = Dewpoint (C)
         DPf = Dewpoint (F)

      Note, there are other ways to measure Dewpoint depending on the
      the sensors. For example, it's more common to measure Dewpoint
      can calculate RH. I used RH since the sensors cost less.

   Ok, now for the Heat Index... In my weather station, I use lookup tables
for all this...

Input Variables

   t = temperature (in Fahrenheit)
   rh = relative humidity

Output Variables

   heatindex = heat index (in Fahrenheit)

Temporary Variables

   t2 = t * t
   t3 = t2 * t
   rh2 = rh * rh
   rh3 = rh2 * rh

Algorithm

heatindex = 16.923 + 0.185212*t + 5.37941*rh - 0.100254*t*rh + (0.941695e-2)
*t2 + (0.728898e-2)*rh2 + (0.345372e-3)*t2*rh - (0.814971e-3)*t*rh2 +
(0.102102e-4)*t2*rh2 - (0.38646e-4)*t3 + (0.291583e-4)*rh3 + (0.142721e-5)*
t3*rh + (0.197483e-6)*t*rh3 - (0.218429e-7)*t3*rh2 + (0.843296e-9)*t2*rh3 -
(0.481975e-10)*t3*rh3

   - Tom

At 02:35 PM 10/30/00 -0600, Scott Newell wrote:
>Hi.
>
>Anyone got a good link to formulas for calculating heat index and wind chill?
>
>
>thanks,
>newell


------------------------------------------------------------------------
Tom Handley
New Age Communications
Since '75 before "New Age" and no one around here is waiting for UFOs ;-)

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