Brrr!! It’s cold outside, and the temperature las night was expected to drop to 0 degrees, and rise up only to a high of 10 on Friday, according to Accuweather. More snow is on the way Friday night, too.
The cold, however, is the more immediate threat. If you think temperatures dropping to 0 are cold, look out! It’s going to feel even worse.
Residents of the Chicago region know that when the National Weather Service issues a wind chill advisory, as it has for tonight through 10 a.m. Friday, that the wind is going to make it feel colder than the air temperature — in fact, as cold as minus 15 to 25 degrees below zero cold overnight. But what’s that really mean?
Let’s take a look.
First, what exactly is wind chill? The website Mental Floss has a page dedicated to the topic, and it describes wind chill as the effect wind has on exposed skin. Wind actually draws heat away from exposed skin, which is one reason a breeze on a hot summer day feels cool.
The National Weather Service gets concerned about wind chill when wind accompanies already frigid temperatures, because that gets dangerous for people. A severe wind chill can cause hypothermia and frostbite — just how quickly depends on the real air temperature and the wind speed. The lower the temperature and the higher the wind, the greater the wind chill — up to a point, anyway. Some reference materials indicate wind speeds of more than 40 mph have little additional chilling effect.
Oddly enough, however, Mental Floss states that wind chill has little effect on inanimate objects except to cool them to air temperature more quickly. Water freezes at an air temperature of 32 degrees, not when the wind chill is 32. So if your car does well starting up at, say 5 below 0, it should start just as well at that temperature when the wind chill is 50 below.
To skin, however, wind chill poses a very real threat.
The National Weather Service wind chill chart shows general ranges for the danger. For example, depending on wind speed, frostbite can occur within 30 minutes:
- At -10 to -15 degrees in calm conditions.
- At 0 degrees when winds are 10 to 15 mph.
- At 5 degrees when winds are 25 to 30 mph.
Frostbite can occur within 10 minutes:
- At between -40 and -57 degrees in calm conditions.
- At -5 degrees when winds are between 30 and 35 mph.
Frostbite can occur within five minutes when:
- At -45 degrees when winds are 10 to 15 mph.
- At -20 degrees when winds are 30 to 35 mph.
- At -10 degrees when winds are 55 to 60 mph.
So what’s the coldest wind chill ever recorded? Mental Floss says that’s a tough one to call because the formula for determining wind chill has been revised many times over the years. But on July 4, 2003, Mental Floss states that an east Antarctica weather station recorded -94 degrees with winds of 75 mph. That’s a wind chill of -150.