Chicago Weather in September

Chicago, Illinois usually sees the last of hot weather in September. Many days have pleasant temperatures and relatively few days this month have rain.

This page gives detailed information on the typical September temperature, precipitation, sun, humidity, wind and storms for Chicago. The numbers here are historical averages based on temperature, rain and snow measurements gathered at Chicago Midway Airport and other climate data from Chicago O'Hare International Airport.

Temperature Weather iconTemperature

77 °F September average high 25 °C
59 °F September average low 15 °C
23 days 70 °F max. or more (21 °C)
17 days 60 °F min. or less (16 °C)

Nearly every day in September warms to over 60 degrees Fahrenheit (16 degrees Celsius) in Chicago. The city averages 11 days this month when the thermometer reaches into the 80s °F (over 26 °C). Temperatures above 100 °F (38 °C) are not expected here during September.

The thermometer dips to 50 °F (10 °C) or below on 5 nights. September does not normally get cold enough for frost.

Rainy Weather iconRain

3.3 in total precipitation 85 mm
8 days of rain

Half the time, Chicago receives 1.9 to 4.2 inches (47 to 107 mm) of rainfall in September. One in four years has drier weather, while another one in four is wetter. None of the precipitation falls as snow.

Sunny Weather iconSun

59 % sunshine
9 days clear skies

The sun's rays reach the ground in Chicago during 59 percent of daylight hours on average in September, for a total of 221 hours in the month. Typically on 9 days this month the sky is mainly clear, with at most 30 percent cloud cover.

Sunlight in September at Chicago lasts for 12 hours and 27 minutes a day on average. The longest day of the month is the 1st with 13 hours and 7 minutes of daylight. By the end of the month, the days have shortened to 11:47 from sunrise to sunset. These durations can vary by a minute or two from year to year.

Humid Weather iconHumidity

71 % September average humidity

The relative humidity in Chicago during September usually peaks at 85 percent in the morning then drops to 55 percent by mid afternoon.

Local Time12 am3 am6 am9 am12 pm3 pm6 pm9 pm
Humidity % 81 84 85 69 57 55 63 76

Windy Weather iconWind

8.9 mph September wind speed average 14.3 kph

September is less windy than most other months in Chicago.

Stormy Weather iconStorms

2 days rainfall of 0.5 inches (13 mm) or more
5 days with thunderstorms in September

Chicago sees a sharp decline in stormy weather during September compared with the previous month.


The weather data here are long-term averages provided by the US National Centers for Environmental Information (NCEI). Temperature and precipitation are 1991-2020 normals while humidity and thunderstorms are 1961-1990 normals.

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