What is wind chill?

SIOUX FALLS, S.D. (KELO) — The human face is central to calculating wind chill.

The public will be hearing about wind chill this weekend and week as predicted highs will be in the single digits or just barely into double digits and lows drop below zero across South Dakota and into parts of southwestern Minnesota and northwestern Iowa.

Here’s where the human face plays a role.

Wind chill involves calculated wind speed at an average height of five feet, the typical height of an adult human face, according to the National Weather Service. The calculation formula incorporates heat transfer theory based on heat loss from the body to its surroundings, during cold and windy days.

Laura Edwards, the state climatologist in South Dakota, said in short, the wind chill is “the feels like temperature.”

“What the wind is doing is blowing away the shallow layer of body heat you have right around your skin,” KELOLAND meteorologist Adam Rutt said. “When it’s windy it pushes that layer away, that’s where you get that wind chill effect from. That’s why it feels a lot colder than it actually is.”

Rutt said the face, nose and fingers can be vulnerable in wind chill. The body will focus on keeping a person warm with more attention to internal organs, Rutt said.

“What’s going to keep you alive? That’s the highest priority for keeping you alive,” Rutt said.

Wind chill is about how fast will exposed skin freeze, Edwards said.

The faster the wind speed, the faster body heat is taken away and the colder it feels, according to the NWS.

The wind chills this weekend into the week may not be as cold as back around Dec. 19 but any breeze will make it feel colder than the actual temperature. The higher the wind and wind gust, the colder it feels, Rutt said.

Wind chills well below zero can cause frostbite in 30 minutes or as quickly as five minutes, Edwards said.

Those were the kinds of conditions residents were feeling at times around the week of Dec. 19. This weekend and upcoming week’s wind won’t be a high as that December stretch.

“When you are looking at wind chills of negative 50 or negative 60, you are talking five minutes, maybe 10 (before frostbite),” Edwards said.

Dangerous wind chills can also cause hypothermia, a condition where the body temperature drops abnormally low, Rutt said. Often hypothermia is associated with someone who has been in a cold, or frozen, body of water, he said.

“If you are outdoors for too long, and we’re talking about wind chills of minus 40 or minus 50, hypothermia can be just as big of concern, outside of any kind of frozen body of water as it would in it,” Rutt said.

Edwards said South Dakota has seen the December predicted dangerous wind chills before.

The Aberdeen area, for example, may see streak of 40 below wind chills every couple of years, she said. It may be a few years between the winters with 40 below wind chills in the Sioux Falls area, Edwards said.