Chicago area residents need to break out their hats and heavy coats as the region is under a freeze warning this week.

The coldest air of the season has already arrived, dropping temperatures below their normal levels and paving the way for fall’s first sub-freezing nighttime temperatures.

Here you will find everything you need to know.

Which areas will be most affected?

A freeze warning has been issued for McHenry, DeKalb, Kane, LaSalle, Kendall and Grundy counties, according to the National Weather Service. This warning goes into effect at 1 a.m. and lasts until mid-morning Wednesday.

A freeze warning is in effect for Northern Cook County, Will County and Kankakee County Wednesday morning, with slightly warmer temperatures possibly helping to avoid a hard freeze.

When do the coldest temperatures occur?

According to the National Weather Service, the coldest temperatures on Wednesday will occur just before dawn, with lows in the upper 20s in the western suburbs.

In parts of the area affected by the frost warning, low temperatures are likely to settle around 30 degrees and slowly warm up after daybreak.

The Chicago area will get a glimpse of winter temperatures this week as a Freeze Advisory and Freeze Advisory go into effect overnight and Wednesday.

Is this type of cold normal this time of year?

In fact it is. In fact, according to the National Weather Service, most of the Chicago area experiences its first frost of fall in mid-October, between October 11th and 20th.

The exact normal date for the first frost in Chicago is October 19th. In areas closer to the lake, this date moves to the last week of the month or even the first week of November due to the proximity to Lake Michigan.

In the remaining suburbs, the first frost typically occurs earlier, around October 13th in Rockford.

In 2023, the first freezing temperature in Chicago did not occur until October 30, when the minimum temperature was 31 degrees. The following day, nearly an inch of snow fell in the city, the first measurable snowfall of the season.

How long will the cold temperatures last?

For those residents who aren’t thrilled about the cold, the good news is that it won’t last long. Temperatures will still be cool on Wednesday, with highs in the mid to upper 50s, but a warming trend will really begin on Thursday.

Forecast models show temperatures will rise back into the upper 60s on Thursday and highs will rise back into the upper 70s across the region on Saturday, with overnight lows in the upper 40s and lower 50s.

These conditions are expected to continue for several more days, with partly to mostly sunny conditions expected.

What about the rain?

Lake effect rain could continue into the overnight hours in the Chicago area, but will slowly drift eastward as winds begin to shift and blow the plume of moisture away from the city.

After the moveout, it is expected to remain mostly dry for several days and the extended forecast does not currently call for a sustained chance of rain.