Weather
Illinois Weather: First Frost Season Nears Chicago
Chicago, IL – Northern Illinois is entering its October frost season, with chilly nights developing outside Chicago, although the immediate forecast keeps most temperatures above frost levels.
By Rachel Monroe · 2026-10-04T13:10:46.219Z
Chicago, IL – Northern Illinois is entering its October frost season, with chilly nights developing outside Chicago, although the immediate forecast keeps most temperatures above frost levels.
According to the National Weather Service in Chicago, dry and seasonable weather will continue through at least the middle of the week. Overnight temperatures will be noticeably cooler away from Chicago’s urban heat island.
The pattern comes as northern Illinois moves deeper into the time of year when gardeners and growers increasingly watch for the first frost. However, the current NWS forecast does not call for widespread frost or freezing temperatures.
Sunday will be sunny with highs from 68 to 74 degrees, although areas near the Lake Michigan shore should remain in the middle 60s. Sunday night lows are forecast from 41 to 47 across the region, while Chicago stays closer to 50.
Monday brings the chilliest morning in the five day outlook. Temperatures outside the city are expected to fall to around 40 to 44 degrees, while Chicago remains in the upper 40s. Afternoon highs will reach 64 to 70, with lower 60s near the lake.
A quick warmup follows. Tuesday highs are forecast from 67 to 73 with overnight lows of 50 to 55. Wednesday turns warmer, reaching 70 to 78 degrees before lows fall to 46 to 53 Wednesday night.
Thursday should bring highs of 67 to 74 and nighttime temperatures from 47 to 54.
For residents waiting on northern Illinois’ first frost, the next several nights will feel increasingly like fall, particularly outside Chicago, but the current forecast keeps temperatures above typical frost levels. Dry, seasonable weather remains the main story through midweek.