NWS wind chill chart shows how long it takes skin to freeze at different wind chill temperatures.
Hopefully, it won’t be long before wind chill babble disappears from the vocabulary of over zealous meteorologists in the Upper Midwest. These “lazy” winter days in Minnesota are like forecasting weather in Arizona. How many different ways can you say “clear and cold?” In Arizona months go by where you have to figure out yet another way to say “sunny & hot.”
Believe it or not, there is a method to the madness of wind chill. People have observed for decades that you feel colder when the wind blows in winter. The NWS quantifies that feels like temperature on your skin through something called “the human face model.”
People often ask me how wind chill is really calculated. If you’re a math wiz, have a crack at the wind chill formula below.
Windchill (ºF) = 35.74 + 0.6215T – 35.75(V^0.16) + 0.4275T(V^0.16)
Where: T = Air Temperature (F)
V = Wind Speed (mph)
^ = raised to a power (exponential)
Now you know why I prefer to use the chart above.
The NWS updated the wind chill chart in the last few years to better reflect the actual heat loss on exposed skin in cold weather. A series of human trials were conducted in wind tunnel conditions with heat sensors attached to the faces of volunteers.
“The NWS Windchill Temperature (WCT) index uses advances in science, technology, and computer modeling to provide an accurate, understandable, and useful formula for calculating the dangers from winter winds and freezing temperatures. The index:
-Calculates wind speed at an average height of five feet, typical height of an adult human face, based on readings from the national standard height of 33 feet, typical height of an anemometer
-Is based on a human face model
-Incorporates heat transfer theory, heat loss from the body to its surroundings, during cold and breezy/windy days
-Lowers the calm wind threshold to 3 mph
-Uses a consistent standard for skin tissue resistance
-Assumes no impact from the sun (i.e., clear night sky).
Windchill Temperature is only defined for temperatures at or below 50 degrees F and wind speeds above 3 mph. Bright sunshine may increase the wind chill temperature by 10 to 18 degrees F.”
It amazes me to see people these days wandering around outside without jackets in Minnesota when it’s 20 degrees outside with a brisk wind. It seems our mentality these days is we can handle anything, who needs a coat? I have often said 20 is the new 40 when it comes to how Minnesotans dress in winter.