Wind Chill Science Revisited

I stumbled across this article on aweathermoment.com with regards to how the “Wind Chill Temperature” is calculated in today’s public forecasts, and the inherent flaws, or rather, extremely simplified assumptions used to translate the values to a “temperature” simply because the public can relate better to a “Feels Like” comment.

From “Brad’s” blog post on Environment Canada’s change in Wind Chill Warning mechanisms;

“As I’ve shown above, there are some egregious assumptions made that oversimplify the reality of how wind chill can be measured. In addition to that, there are fundamental parameters that can be dramatically altered by body type and clothing. The idea that there’s a “one size fits all” solution to wind chill simply isn’t rooted in reality.”

The post referenced a BAMS article from 2005 by RANDALL OSCZEVSKI and MAURICE BLUESTEIN that spoke to the revised US conversion chart updated in 2001, and once again, the weaknesses in the assumptions used to develop the formula.

“Because one’s experience of the equivalent temperature depends on facial skin temperature, which varies from person to person because cheek thermal resistances vary widely, WCT is not an ideal way to express the combined effect of wind and low temperature.”

I doubt the average person knows the exact wind chill conversion formula.

WCT (°C) = 13.12 + 0.6215T – 11.37V^0.16 + 0.3965TV^0.16 (where T is in degrees Celcius and V is in km/hour).

But, as raised by Brad,

“The other thing worth noting is all those weird numbers. Where did 13.12 come from? What’s with 0.6215 and 11.37? I’ve heard of squaring things, but what’s with an exponent of 0.16?

Those are all coefficients that were determined in the linear regression of the series of equations to produce a single equation that requires only wind speed and temperature. To put it in simpler terms, those numbers are assumptions.”

He goes on to talk about how the simplified formula itself, while expressed in degrees Celsius, is in fact unitless, or rather produces a value that is not the scientific equivalent of “temperature”.

Additionally the various components used to make up the simplified formula include:

– Height of face

– Width of face

– Walking speed

– Body thermal conductance

– Wind power exponent

– Wind speed

– Air temperature

The first 4 vary widely from person to person based on genetics and clothing.  And if we account for the uncertainty, the value has little to no accurate meaning;

 

Maybe its not as interesting to you, but Wind Chill has always been a beef of mine, due to the way its presented as something the average person can gauge, when most people have no idea what the temperature is based on how their skin feels.  /rant

 

PMB_Z

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