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PostPosted: Wed Feb 06, 2019 9:44 pm 

Joined: Thu Jul 15, 2004 3:42 pm
Posts: 35
Location: Kansas
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 8419 times ]
PostPosted: Wed Feb 20, 2019 8:42 pm 

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