Chicago Weather in August

Chicago's summer weather grows stormier in August. The month receives much more rain than any other. Yet between storms August has more clear days than most months.

This page gives detailed information on the typical August weather for Chicago, Illinois.

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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

82 °F August average high 28 °C
63 °F August average low 17 °C

In most years, Chicago averages a daily maximum temperature for August that's between 79 and 85 degrees Fahrenheit (26 to 29 degrees Celsius). The minimum temperature usually falls between 60 and 66 °F (15 to 19 °C).

The days at Chicago begin to cool during August. By the end of the month, the temperature has dropped around 3 °F (2 °C) below what it was at the start.

19 days 80 °F max. or more (27 °C)
27 days 70 °F min. or less (21 °C)

Nearly every day in August warms to over 70 °F (21 °C) in Chicago. The city averages 4 days this month when the thermometer reaches into the 90s °F (over 32 °C). Temperatures above 100 °F (38 °C) are not expected here during August.

The thermometer dips to 60 °F (16 °C) or below on 10 nights. But only rarely does August get as cold as 50 °F (10 °C).

Rainy Weather iconRain

4.9 in total precipitation 124 mm
10 days of rain

August is Chicago's rainiest month of the year. Half the time, Chicago receives 3 to 7 inches (63 to 168 mm) of rainfall in August. One in four years has drier weather, while another one in four is wetter.

Sunny Weather iconSun

62 % sunshine
9 days clear skies

The sun's rays reach the ground in Chicago during 62 percent of daylight hours on average in August, for a total of 265 hours in the month. Typically on 9 days this month the sky is mainly clear, with at most 30 percent cloud cover.

Sunlight in August at Chicago lasts for 13 hours and 48 minutes a day on average. The longest day of the month is the 1st with 14 hours and 24 minutes of daylight. By the end of the month, the days have shortened to 13:10 from sunrise to sunset. These durations can vary by a minute or two from year to year.

Humid Weather iconHumidity

71 % August average humidity

The relative humidity in Chicago during August 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 85 85 67 57 55 61 75

Windy Weather iconWind

8.2 mph August wind speed average 13.2 kph

The wind is calmest in Chicago during August.

Stormy Weather iconStorms

3 days rainfall of 0.5 inches (13 mm) or more
6 days with thunderstorms in August

More heavy rainstorms drench Chicago in August compared with other months. The city averages two days this month when a downpour drops at least an inch (25 mm) of rain.


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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