Chicago
Illinois, USA
Long-term weather forecast
Long-term weather forecast

September weather forecast and climate
Chicago, IL

An aerial view of the city of Chicago in Illinois, on the shores of Lake Michigan, with a superb view of the sandy beach of Oak Street
An aerial view of the city of Chicago in Illinois, on the shores of Lake Michigan, with a superb view of the sandy beach of Oak Street
September is one of the best times to visit Chicago in the beautiful autumn season. The weather is usually calm with warm temperatures that average in the 54°F (12.2°C) to 75°F (23.9°C) range. A few days cross 80°F (26.7°C), but it is rare to record temperatures above 90°F (32.2°C). Nights are comfortable and seldom drop below 40°F (4.4°C).
September sunshine lasts for a daily 12 hours, while rain is moderate to the tune of 3.2" (81.3mm), there are clear skies for many days. Leaves start to change colors by mid to the third week of September, and the temperatures gradually cool down by the end of the month.
  • Average high temperature in September: 75.3°F

The warmest month (with the highest average high temperature) is July (84.2°F).
The month with the lowest average high temperature is January (31.5°F).

  • Average low temperature in September: 57.5°F

The month with the highest average low temperature is July (67.5°F).
The coldest month (with the lowest average low temperature) is January (18.2°F).

  • Average humidity in September: 71.1%

The month with the highest relative humidity is December (75.5%).
The month with the lowest relative humidity is May (64.1%).

  • Average rainfall in September: 3.3"

Wettest months (with the highest rainfall) are May and June (4.1").
The driest month (with the lowest rainfall) is February (1.9").

  • Average rainfall days in September: 8.2 days

The month with the highest number of rainy days is May (11.4 days).
The month with the lowest number of rainy days is September (8.2 days).

  • Average snowfall in September: 0"

The month with the highest snowfall is January (11.5").
Months with the lowest snowfall are May, June, July, August and September (0").

  • Average snowfall days in September: 0 days

The month with the highest number of snowfall days is January (8.1 days).
Months with the lowest number of snowfall days are May, June, July, August and September (0 days).

  • Average sea temperature in September: 68.6°F

The best month for swimming (with the highest average sea temperature) is August (73.9°F).
The coldest month (with the lowest average sea temperature) is February (36.9°F).

  • Average daylight in September: 13.4h

The month with the longest days is June (Average daylight: 16.3h).
The month with shortest days is December (Average daylight: 10.2h).

  • Average sunshine in September: 7.6h

The month with most sunshine is June (Average sunshine: 10.4h).
The month with least sunshine is December (Average sunshine: 3.4h).

  • Average UV index in September: 6

Months with the highest UV index are June and July (UV index 9).
Months with the lowest UV index are January and December (UV index 1).

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