What Does it Take to Get a Wind Chill Warning? Chicago’s All-Time Record Low

A Wind Chill Advisory is announced when “Dangerous wind chills of -20°F to -30°F.

A Wind Chill Warning is announced when Extreme wind chills of -30°F or colder.

The average low for today’s date in Chicago is 14°F and the average high for this date is 29°F. Even though the days are getting longer and sunshine is getting slightly warmer, there is a lag of temperatures called seasonal lag.

Seasonal lag is the phenomenon whereby the date of maximum average air temperature at a geographical location on a planet is delayed until some time after the date of maximum insolation, which is a measure of solar radiation energy received on a given surface area in a given time. This also applies to the minimum temperature being delayed until some time after the date of minimum insolation.

If seasonal lag did not exist, the coldest days of the year would tend to fall around the Winter Solstice about December 21.

The all-time record low for Chicago is -27°F — that’s not wind chill that’s the regular temperature. The record low occurred on January 20, 1985. Notice that’s the same as today’s date.

The wind chill at the time of the all-time record low in Chicago on January 20, 1985 was about -53°F at about 7:00 a.m.

The wind chill actually might have been a little colder at 10:00 a.m when the air temperature was -22°F but the wind gusted to 26.5 mph — that’s -54°F.

The National Weather Service 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).

More info …
See the National Weather Service Wind Chill Index page for more information. The web page from the National Weather Service includes a table and a calculator.