Much of the northern Illinois area is expected to experience heavy rainfall Monday evening and high winds amid unseasonably warm weather. | Graphic: NWS Chicago

The National Weather Service is warning about heavy rainfall and possible thunderstorms Monday evening in the Chicagoland area amid unseasonably warm weather.

The National Weather Service (NWS) issued a hazardous weather outlook early Monday morning for much of Illinois.

The outlook covers Lake, McHenry, Boone, Cook, Will, Winnebago, Ogle, Lee, DeKalb, Kane, DuPage, LaSalle, Kendall, Grundy, Kankakee, Livingston, Iroquois and Ford counties.

The NWS said there is a slight chance of thunderstorms Monday afternoon. Thunderstorm chances will increase on Monday evening.

A very low chance of localized severe weather could develop.

“If severe weather were to occur, localized damaging winds would be the primary threat,” the outlook said.

The weather service said the greater concern is areas receiving heavy rainfall Monday evening.

The NWS said rain could be enough to result in flash flooding in low-lying and poor-drainage areas.

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Many areas will see one to two inches of rain with totals of up to four inches possible.

Motorists are recommended to use caution when driving in heavy rain and stay up to date on the forecast, the NWS said. People should move indoors when they hear thunder.

After 8 p.m. Monday, wind gusts over 40 mph are possible, especially in the Chicago area and south and east of the Interstate 57 corridor, including northwest Indiana. High winds will continue into Tuesday.

The NWS called the weather “unseasonably warm and muggy.”