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 weather for Chicago.

You can jump directly to data and descriptions for:

The numbers here are historical averages based on climate data gathered at the Chicago O'Hare International Airport, located in the northwestern part of Chicago.

Temperature Weather iconTemperature

75 °F September average high 24 °C
54 °F September average low 12 °C

In most years, Chicago averages a daily maximum temperature for September that's between 72 and 78 degrees Fahrenheit (22 to 25 degrees Celsius). The minimum temperature usually falls between 52 and 57 °F (11 to 14 °C).

The days at Chicago cool down quickly during September. By the end of the month, the temperature has dropped around 11 °F (6 °C) below what it was at the start.

21 days 70 °F max. or more (21 °C)
22 days 60 °F min. or less (16 °C)

Nearly every day in September warms to over 60 °F (16 °C) in Chicago. The city averages 9 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 9 nights. About once a decade September has a night that's cold enough for frost.

Rainy Weather iconRain

3.2 in total precipitation 82 mm
8 days of rain

Half the time, Chicago receives 1 to 4 inches (31 to 99 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.


These weather data are long-term historical averages provided by the National Climatic Data Center of the United States. The temperature and precipitation numbers are 1981-2010 normals while the humidity and thunderstorm statistics are 1961-1990 normals.

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