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Heat Index

26th July 2005, 02:29 pm by Dick Kusleika

They say that if you don’t like the weather in Nebraska, just wait five minutes. Of course they say the same thing for every place in the United States, except maybe San Diego and Miami.

According to weatherimages.org you can calculate the heat index if you know the dry air temperature and the relative humidity. All you need is this simple formula:

=ROUND(16.923+((1.85212*(10^-1))*A2)+(5.37941*B2)-((1.00254*(10^-1))*A2*B2)+
(9.41695*(10^-3)*(A2^2))+(7.28898*(10^-3)*(B2^2))+(3.45372*(10^-4)*(A2^2)*B2)-
(8.14971*(10^-4)*A2*(B2^2))+(1.02102*(10^-5)*(A2^2)*(B2^2))-(3.8646*(10^-5)*(A2^3))+
(2.91583*(10^-5)*(B2^3))+(1.42721*(10^-6)*(A2^3)*B2)+(1.97483*(10^-7)*A2*(B2^3))-
(2.18429*(10^-8)*(A2^3)*(B2^2))+(8.43296*(10^-10)*(A2^2)*(B2^3))-(4.81975*(10^-11)*(A2^3)*(B2^3)),0)

where A2 is the temperature and B2 is the relative humidity. Here’s Omaha’s calculation for yesterday and today:

excel range showing heat index of 105 and 76 on consecutive days

People have been complaining about the excessive heat for a week around here. Not me. It won’t be long until I’m shoveling my driveway, so I’m counting my blessings.

(Thanks, DA, for the link to the formula.)

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4 Comments

  1. Dave:

    There must be some lower limit for where this formula becomes irrelevant. For example, I opened a new workbook and pasted the formula into C2. With everything else blank, that meant Temperature=0 and Humidity=0. It gave me a heat index of 17! And if I set Humidity to 50, I got 308…

    27 July 2005, 11:36 am

  2. Hui...:

    The http://www.weatherimages.org/data/heatindex.html site only has tables from 90-105 F, that would answer your query.

    28 July 2005, 5:54 am

  3. Rich:

    Thanks, Dick. I showed this to a co-worker:

    Here response was, “Heat Index? Am I sweating????”

    LOL

    28 July 2005, 7:46 am

  4. Scott:

    Thanks for the formula, now I can actually give people an indication of how hot it really can get in South Dakota! I’m sick of people saying it’s all “dry heat!”

    20 November 2005, 6:40 pm

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