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Illinois Weather and climate

Data source:Meteostat
Update date:2025-09

Illinois year round climate
  • Spring (March–May): Average 44–67°F, gradually warming climate with abundant rainfall, but significant temperature fluctuations. Common activities: Outdoor excursions, flower viewing. Recommended clothing: Layered clothing, jacket, long-sleeved shirts, comfortable shoes.
  • Summer (June–August): Average 75–75°F, hot and humid with higher rainfall, occasional thunderstorms. Common activities: Swimming, camping, outdoor BBQ. Recommended clothing: Light and breathable clothing, sun hat, sunglasses.
  • Autumn (September–November): Average 67–44°F, gradually decreasing temperatures, pleasant weather, reduced rainfall. Common activities: Maple viewing, hiking, harvesting crops. Recommended clothing: Comfortable long-sleeved shirts, light jacket, warm clothing.
  • Winter (December–February): Average -35–35°F, cold and dry, snowfall varies by year. Common activities: Skiing, ice skating, indoor activities. Recommended clothing: Warm clothing, thick jacket, hat, gloves, scarf.
Illinois climatological average

Annual average temperature: approx. 54.7°F / Annual rainfall: approx. 1179 mm / Summer humidity: 60%–75% / Rainiest month: August

Illinois monthly average temperature and precipitation
Month
Air temperature (°F)
Precipitation (mm)
January
28.8°F
69.9
February
34.7°F
92.4
March
44.1°F
121.3
April
53.8°F
113.8
May
67.3°F
108
June
75°F
114.6
July
75.7°F
151.9
August
73.8°F
163.7
September
67.6°F
53.4
October
56.1°F
61.5
November
44.2°F
80.9
December
35.6°F
48.4
Illinois weather for the next seven days
10/15
Wednesday
Sunny
77.9°F/56.8°F
10/16
Thursday
Cloudy
78.1°F/58.6°F
10/17
Friday
Cloudy
73.6°F/54.1°F
10/18
Saturday
Moderate rain
71.6°F/60.3°F
10/19
Sunday
Sunny
63.3°F/48.7°F
10/20
Monday
Sunny
69.8°F/44°F
10/21
Tuesday
Sunny
79.7°F/50.7°F