Digital Atmosphere using pre-2001 Wind Chill Formula

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Posts: 46
Joined: Thu Jul 15, 2004 3:42 pm
Location: Kansas

Digital Atmosphere using pre-2001 Wind Chill Formula

Post by geophi »

Hi Tim,

It appears as if DA 3.10a is still using the pre 2001 wind chill formula when calculating wind chills. Below is a graphic.

For the site circled in red in South Dakota (KD07), the temperature in Fahrenheit is plotted as -4 (-20.0C in the QC window) and the wind is from the north at 18 kts. DA plots the wind chill in Fahrenheit as -45 (lower right number on the plot for D07). The NWS webpage on the left has the wind chill calculator using the formula in use since 2001. Plugging in the -20.0C temp and 18 kt wind, gives a wind chill in Fahrenheit of -27.6.

Could this be fixed, or an additional Wind Chill value added for the newer formula? Thanks.

DA_Old_Wind_Chill.jpg (226.66 KiB) Viewed 18599 times

Tim Vasquez
Posts: 527
Joined: Sat Nov 22, 2003 10:47 pm

Re: Digital Atmosphere using pre-2001 Wind Chill Formula

Post by Tim Vasquez »

Looking around at the current formulas, it does look like we need to update it.

Here is the formula we have been using so far. I will make some changes to add the new index and allow access to the old formula for those that want to use it.

function windchill(tempc:real;windspd:real):real;
ftemp, workvalue : real;
ftemp := ctof(tempc);
if (windspd < 4) then windspd := 4;
workvalue := ((((33 - (10.45 + (10 * sqrt (windspd /
1.943)) - (windspd / 1.943)) * (33 - ((ftemp - 32)
* 0.5556)) / 22.04) / 0.5556) + 32));
result := workvalue;

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