Wind Chill: It Makes For An Extra Chilly Day!

Cold weather can be miserable on its own but adding wind into the mix can make winter weather feel even worse.

Wind chill is defined as the apparent temperature of an air flow over human skin. On breezy days, the wind will carry heat away from the human body leading to the body getting colder faster. The equation meteorologists use to calculate wind chill was derived from experimental data and is reliant on a few key assumptions and simplifications.

The calculation is based on winds hitting a human face with no influence inferred from the sun. Winds for this calculation are first reduced to an estimated flow at 5 feet above ground level based on wind observations taken from 33 feet up, or around 10 meters. That may seem arbitrary at first, but most automated weather stations take wind observations around this height by convention so it’s a necessary assumption.

Wind chill, like its close relative heat index, is not calculated at all temperatures and for all wind speeds. While there may be a slight wind chill when a 10-mph wind occurs on a 60 degree day, it won’t be very noticeable. The cut-offs for wind chill calculations are 50 degrees and 3 mph for this reason.

While the equation to calculate wind chill is complicated, using wind chill isn’t. A stronger wind will produce a lower wind chill temperature, leading to colder skin and a higher risk of cold-related illnesses like hypothermia and frostbite.

When wind chills are in play, it’s a very good idea to cover as much skin as possible especially on days where air temperatures will already be below freezing. Be sure to do your best to stay dry as well, as evaporation from wet clothes and skin will only serve to cool your body faster.

It’s also worth keeping in mind that certain wind chill values can be used to estimate how quickly frostbite will set in on unprotected skin in that environment. When the wind chill is below negative 17 degrees, frostbite will likely set in within 30 minutes, with frostbite likely after 5 minutes when the wind chill is below negative 50 degrees.

Winter weather can turn dangerous in a hurry, but only if proper precautions aren’t taken. Hopefully, this advice will help you use wind chill as a tool to assess risk when cold weather comes to town.

Source: NWS

Story Image: The University of Wisconsin-Madison on a frigid day. (Corey Coyle via Wikimedia Commons)