Chicago Weather

What is a red flag warning? What to know as alert issued in parts of Chicago area

The warning begins at 12 p.m. for several Chicago-area counties

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Editor's Note: Our updated weather story for Tuesday, Feb. 27 can be found here. Our original story continues below.

A red flag warning was issued across parts of the Chicago area Monday, but what does it mean and what should residents watch for?

The warning begins at 12 p.m. for McHenry, Kane, DuPage, Kendall, Grundy, Will, Kankakee, DeKalb and LaSalle counties in Illinois.

It remains in effect until 6 p.m.

Here's an explanation:

What is a red flag warning?

According to the National Weather Service, a red flag warning "means that critical fire weather conditions are either occurring now, or will shortly."

"A combination of strong winds, low relative humidity, and warm temperatures can contribute to extreme fire behavior," the alert states.

What's happening in the Chicago area?

In the counties under the alert, wind gusts of up to 35 mph are possible Monday, while relative humidity levels drop as low as 18 percent.

"Dry fuels, low relative humidity, and strong winds will create conditions favorable for the rapid spread of wildfires," the alert states.

The weather service warned that grass or brush fires ignited during the red flag warning could "rapidly" spread out of control.

"Strong south winds, gusting over 30 mph, record warm temps, & very dry conditions will make make it so that any brush fires that start will spread rapidly & become difficult to control," NWS wrote on X, formerly known as Twitter, Monday morning. "Exercise extreme caution disposing of smoking materials, consider postponing outdoor burning."

What's next?

The warning comes amid potentially record-breaking warmth for the Chicago area.

According to the NBC 5 Storm Team, Monday afternoon could see temperatures reaching well above 60 degrees.

The average high for Feb. 26 is 40 degrees, NBC 5 Storm Team Meteorologist Alicia Roman said. Monday's predicted high temperature will be significantly warmer, at 69 degrees. That temperature is expected to break a record high temperature, set in 2000, of 64 degrees, Roman said.

"Some areas could hit 70," Roman said.

Other areas are expected to remain in the mid- to upper- 60s, Roman added.

Overnight Monday, parts of the Chicago area could see a low chance for showers or isolated thunderstorms, Roman said.

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