September weather forecastChicago, IL
September
Weather in September
September is a transitional month in Chicago with a shift from warm summer days to the mild and pleasant days of fall. The significant decrease in temperature from August makes this month a comfortable time with ample daylight hours and robust sunshine. Receive autumn with open arms, as the city turns into vibrant hues of orange, red, and yellow. The cooler evenings set in, providing a delightful contrast to the warm sunny days.Temperature
With the onset of September, Chicago experiences a modest temperature adjustment, with the average high-temperature gently receding from a warm 77.5°F (25.3°C) in August to a pleasant 71.1°F (21.7°C). An average nighttime temperature of 61.2°F (16.2°C) is observed during September.Humidity
In Chicago, the average relative humidity in September is 75%.Rainfall
In Chicago, during September, the rain falls for 14.5 days and regularly aggregates up to 3.23" (82mm) of precipitation. In Chicago, during the entire year, the rain falls for 160.2 days and collects up to 36.97" (939mm) of precipitation.Snowfall
June through October are months without snowfall.Ocean temperature
In Chicago, the average seawater temperature in September is 68.5°F (20.3°C).Note: Most people find it challenging to enjoy swimming in water that is 68.5°F (20.3°C). As water temperature falls below 69.8°F (21°C), controlling breathing grows increasingly difficult.
Daylight
In September, the average length of the day is 12h and 28min.On the first day of the month, sunrise is at 6:17 am and sunset at 7:23 pm. On the last day of September, sunrise is at 6:47 am and sunset at 6:33 pm CDT.
Sunshine
The average sunshine in September is 9.1h.UV index
In Chicago, the average daily maximum UV index in September is 4. A UV Index value of 3 to 5 symbolizes a moderate health risk from unprotected exposure to Sun's UV rays for ordinary individuals.Note: A daily maximum UV index of 4 in September translates into the following instructions:
Act with care - The need to guard against sun damage is communicated. The Sun's most harmful UV rays are emitted around midday; avoid staying outdoors for long during this time. Wearing a wide-brim hat can block approximately 50% of UV radiation, protecting the eyes.
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
Average temperature in September
Chicago, IL
- Average high temperature in September: 71.1°F
The warmest month (with the highest average high temperature) is August (77.5°F).
The month with the lowest average high temperature is January (29.7°F).
- Average low temperature in September: 61.2°F
The month with the highest average low temperature is July (67.8°F).
The coldest month (with the lowest average low temperature) is January (20.7°F).
Average pressure in September
Chicago, IL
- Average pressure in September: 30.03"Hg
The month with the highest atmospheric pressure is January (30.11"Hg).
The month with the lowest atmospheric pressure is June (29.92"Hg).
Average wind speed in September
Chicago, IL
- Average wind speed in September: 9.3mph
The windiest month (with the highest average wind speed) is January (12.5mph).
The calmest month (with the lowest average wind speed) is July (7.7mph).
Average humidity in September
Chicago, IL
- Average humidity in September: 75%
The month with the highest relative humidity is January (82%).
The month with the lowest relative humidity is October (73%).
Average rainfall in September
Chicago, IL
- Average rainfall in September: 3.23"
The wettest month (with the highest rainfall) is June (4.88").
The driest month (with the least rainfall) is December (1.65").
Average rainfall days in September
Chicago, IL
- Average rainfall days in September: 14.5 days
The month with the highest number of rainy days is July (18.5 days).
The month with the least rainy days is February (5.5 days).
Average snowfall in September
Chicago, IL
- Average snowfall in September: 0"
The month with the highest snowfall is February (3.54").
The months with the least snowfall are June, July, August, September and October (0").
Average snowfall days in September
Chicago, IL
- Average snowfall days in September: 0 days
The month with the highest number of snowfall days is January (10.6 days).
The months with the least snowfall days are June, July, August and September (0 days).
Average sea temperature in September
Chicago, IL
- 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 /
Average sunshine in September
Chicago, IL
- Average daylight in September: 12h and 30min
The month with the longest days is June (Average daylight: 15h and 12min).
The month with the shortest days is December (Average daylight: 9h and 12min).
- Average sunshine in September: 9h and 6min
The months with the most sunshine are July and August (Average sunshine: 10h and 36min).
The month with the least sunshine is January (Average sunshine: 3h and 42min).
Average sunshine days in September
Chicago, IL
- Average sunshine days in September: 12.1 days
The month with the most sunshine days is December (15.5 days).
The month with the least sunshine days is July (9.3 days).
Average UV index in September
Chicago, IL
- Average UV index in September: 4
The months with the highest UV index are July and August (UV index 6).
The months with the lowest UV index are January and December (UV index 1).
Average cloud cover in September
Chicago, IL
- Average cloud cover in September: 30
The month with the most cloud cover is January (Cloud cover 62).
The months with the least cloud cover are July and August (Cloud cover 27).
Average visibility in September
Chicago, IL
- Average visibility in September: 6mi
The months with the highest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).
The months with the lowest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).
