Wind Chill

 

Weather reports and forecasts are almost as bad as commercials: they all make it abundantly clear that they consider their audience too stupid to understand simple relationships, in particular the possibility that our experience of getting cold depends on two variables in different ways. The temperature of the air is one factor; the transport of heat by that air is another. The latter depends on how rapidly the warmed-up air next to your skin is replaced by new cold air. That is, upon your clothing and upon the wind.

We hear, "The temperature is minus five, but with the wind chill factor it feels like minus twenty-two."

No it doesn't! It feels like minus five with a wind.

They never tell us what the wind speed is, but we can look it up separately. Consulting the table on WikipediA's "Wind chill" page reveals that (assuming US units) -5 F supposedly "feels like" -22 F if the wind speed is 10 mph. So let's assume the wind speed is 10 mph.

Does -5 F in a 10 mph wind really feel like -22 F (presumably in still air, although they never specify that)? Hell no! It feels like -5 F in a 10 mph wind! Who among us could not tell the difference? Would you dress the same for both, ignoring the penetrability of that bulky sweater that keeps you cozy warm in still air? Let's hope not. If so, how many people have frozen to death in windy -5 F weather because they blindly accepted the idiotic distortions of weatherfolks? Perhaps a class action suit is in order.

The WikipediA page also informs us that, "The wind chill temperature is never higher than the air temperature, and the windchill is undefined at higher temperatures (above 10oC [50oF]). Humidity on the skin can result in a higher perceived air temperature, which is accurately termed the heat index (or humidex), and is used instead; note however that heat index figures do not include any reference to wind speed."

How dumb is that? The same factors that determine how fast you lose heat due to thermal contact with the air determine how fast the sweat on your skin will evaporate - our bodies' main mechanism for thermal regulation at high temperature. So still air with high humidity is a killer; that's why we invented fans a few thousand years ago. Air with lower water content will keep you cooler; so will a nice breeze. But we are too stupid to grasp such complex relationships. The best our self-appointed caregivers can do is to report a "humidex" in the form of, "Feels like a hundred degrees!"

No it doesn't. Not unless it is a hundred degrees.

 

Published by Jess

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