What's the deal with the heat index?

[Bill McBlueState]

Is there a formula? Or is just something the weather people make up to sound more dramatic?

Here it's 95 with a heat index of 108. So even if it doesn't hit 100 today, all the evening newscasters will get to flash a big, scary three-digit number everywhere.

I smell a scam.

[Avalux]

1. It's a formula, based on humidity level.

I'm not sure of the specifics, but the higher the humidity the hotter it feels because it impedes a person's ability to perspire. Make sense?

[Bill McBlueState]

4. ok, I can see that

It has something to do with how quickly moisture evaporates given the humidity and temperature. Thanks!

[Mutley]

2. Heat index is the temperature the body feels

when heat and humidity are combined.



http://www.crh.noaa.gov/pub/heat.php

[Bill McBlueState]

3. ooh, a chart

Thanks!

Yeah, that's consistent with what I'm seeing here. 95 degrees, 55% humidity, heat index of 108.

I wonder how they come up with that. How hot it "feels" seems pretty subjective.

[Mutley]

5. There's a formula they use to figure it out,

but I'm not sure what it is.

[Bill McBlueState]

7. i found one on wikipedia

(see below)

what a mess!

[Mutley]

10. Yeah, I wanted to be a meteorologist

but I can't handle those crazy equations. :silly:

[Bill McBlueState]

6. holy crap, this is some formula!

As usual, Wikipedia is your friend...

Apparently the scale *is* based on subjective reports of how hot people feel under different combinations of temperature and humidity.

Here's a relatively simple rendition of the formula...



All the c's are numerical constants, T is the temperature, and R is the relative humidity.

And there's another one involving matrix multiplication. Oooh, matrix multiplication.

[HiFructosePronSyrup]

8. It's not a scam.

I thought the same thing when I first heard about it. Thought it was some sort feel-good pschyobabble mumbo-jumbo about "feeling hotter." Turns out it's got a legitimate scientific basis. Wind-chill does too.

[Bill McBlueState]

9. lol

feel-good pschyobabble mumbo-jumbo about "feeling hotter."

Pretty much what I was thinking. But it looks like they've got the numbers to back it up.

[Oeditpus Rex]

11. But do we need to know this?

I do think it's a scam of sorts — not mathematical or physical, but a marketing scam designed to attract more viewers to the Weather Channel and the 5/6/10/11 o' clock news and Action Weather. :eyes:

Just tell me "It's gonna be fucking hot" or "It's gonna be fucking cold," okay, Mr. and Ms. Helmet-Hair Meteorologist?

Edit: Or "It's gonna fucking rain."

[Bill McBlueState]

12. there might be a market for that

"The Misanthropic Weather Guy"

That would make a good segment after the last commercial break on the Daily Show.

"Don't forget your goddamn umbrellas, you idiots; it's gonna fucking rain. I will intentionally drive through puddles if I pass you on the street and you're running around like a drowned fucking Smurf."

[liontamer]

13. it's useful to know for preventing heat stroke

90 degree weather with low humidty, grandma can take a walk. If her thermometer reads 90 but the humidty is 90%, she'll over heat much more quickly while taking that same walk. It's better to have an idea before you go out than to wait till you feel the first signs of heat exhaustion