Originally published August 12, 2015.
As I have alluded, the calculation for Heat Index– the “feels like” temperature– has associated with it a number of assumptions:
- All raw temperature and humidity readings are taken in the shade.
- There is a lower bound on both temp & humidity readings.
- (And, technically speaking if I’m reading the literature correctly, an upper bound on relative humidity at really really hot temperatures that don’t typically obtain in real life placed where people live.)
There’s another assumption that especially interests me and it is the assumption of surface area.
The whole entire idea of a heat index– as I, in my Country Mouse ignerance understans, it– is based on cooling. To the regression line that is the heat index, you and I are nothing more than surface areas maintained at a more or less (that’s ± for you folks who don’t understand statistics, “more or less” being the more honest phrase) constant temperature of 98.6°F. The rate at which our surface areas cool is related to the temperature and relative humidity, and to how big we are. And– and I bet you didn’t know this– what kinds of clothes we are wearing!
All of these factors are built into the calculation of the Heat Index AS ASSUMPTIONS.
The assumptions are 5’7″ tall and 147 lbs.; long trousers and short sleeves shirt (84% of body covered).
In my dreams I am 5’7″ but I’ve got a ways to go before I hit 147. I have discovered that loose long pants are actually cooler than short cut offs– but maybe I’m getting old.
The minor point is that what it feels like for me on any given day where the ambient temperature in the shade is greater than or equal to 80°… may not be what it feels like for you.
The major point is this. We know a LOT about the weather and our local environs. That’s not right. I should have worded that passively. A lot is known. I’d venture to say “we” don’t know very much at all.
People just don’t ask questions anymore. And that’s too bad for people. People should be asking, “If the temperature is 79°F and the relative humidity– what does that mean?– is 72% and I have a surface area of … what does it feel like for me?”
We put a man on the moon. Why oh why can’t you tell me what it feels like when it’s …
“Spot on, Rocky! You poor fellows can’t even sweat.”
“What?What? I do say! What?”
“Sorry, Missy. We were just talking about the weather.”