Thursday, December 07, 2006

Wind Chill and Heat Index Formulas

OK, I'm writing this because nobody seems to have an easy to copy and paste formula out there for coders or even for spread sheets.

It's all fine-and-dandy that somebody understands all the ins-and-outs of weather and the math behind it, but sometimes we just want to display the Wind Chill or Heat Index, and that's it. I don't need to know all about the weather ... some of us have deadlines to meet. These formulas are for those of you who are of a similar mind set.

Here are the formulas to calculate the Heat Index and the Wind Chill in spreadsheets and for PHP scripts (programs)...

Heat Index:

Should be calculated only when air temperatures are greater than 80°F (27°C), dew point temperatures are greater than 60°F (16°C), and relative humidities are higher than 40%.


Where A1 holds the TEMP, and B1 holds the HUMIDITY.


The variables should be self explanitory.

Wind Chill:

Should only be calculated when temperatures are at or below 50°F and wind speeds are above 3 MPH. Bright sunshine may increase the wind chill temperature by 10°F to 18°F.


Where A1 holds the TEMP and B1 holds the WIND VELOCITY (SPEED).


Again, the variables should be self explanitory.

I hope this helps somebody, to keep them from spending an hour debugging their code while it was a simple typo that may have messed them up.

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