Monday, June 22, 2009

It's not the heat...

It's the humidity.

This is from the weather history for Little Rock yesterday

Mean Temperature.....85 °F
Max Temperature......95 °F
Min Temperature......74 °F

Dew Point............72 °F
Average Humidity.....65
Maximum Humidity.....94
Minimum Humidity.....36

Then I went to this other cool website to calculate the Heat Index, which has this to say about Heat Index:

What Is Heat Index?
Heat index (HI) is sometimes referred to as the "apparent Temperature". The HI, given in degrees F, is a measure of how hot it feels when relative humidity (RH) is added to the actual air temperature.

The following equation approximates the heat index. There are many assumptions made to produce this, far too many to list here. The equation was obtained by multiple regression analysis and there is a ±1.3 degree °F error.

HI = -42.379 + 2.04901523T + 10.14333127R - 0.22475541TR - 6.83783x10 -3 T 2 - 5.481717x10 -2 R 2 + 1.22874x10 -3 T 2R + 8.5282x10 -4 TR 2 - 1.99x10 -6 T 2 R 2


T = ambient dry bulb temperature degrees Fahrenheit
R = relative humidity

Yeah... whatever. More importantly there was a calculator that you could plug in the numbers, click on the "Calculate HI" and it magically gave you the Heat Index. The answer was an invigorating 103 degrees.

Take that 103 degrees and place yourself in some hilly woods. Let's add a little more by imagining there's a breeze, but you can't feel it. You're almost there: you are hot, it's humid, there's no breeze. Are you drenched in sweat yet? No? How about one more little thing to make the experience complete, 1.5 - 2 hours of physical exertion! Sounds like fun, huh?

There were about 10 of us that ended up making the trip from Texas for the 3 Legged Dawg race in Little Rock. While just surviving the heat/humidity seemed to be a major accomplishment, most of the group made it to the podium.

It was a fun trail and except for the added misery brought on by the high Heat Index issue it was a fun race. I'm glad we made the last minute decision to go, just wish we had a portable a/c unit to mount on the bike.

1 comment:

zero said...

my problem with heat index is that it exaggerates the perceived heat. i think it should be baselined at 40 or 50% humidity instead of 0% humidity. That way when it's 95 in Arizona with zero humidity, you can say yeah but the heat index is only 80 (or so, i didn't plug in the formulas, sorry, what am i a math major?)

Of course using the same formula it would have "only" felt like 99 not 103 at your race. See doesn't that make you feel cooler already?

I wonder if the portable a/c unit on your bike violates any self sufficiency MTB rules? I suppose as long it is battery powered and you don't have to run a long plug back to the start line, you are probably ok there.