Decatur (IL) Weather & Climate: Best Time to Visit

Depending on the time of the year, temperatures range from comfortable to chilly in Decatur. Average maximum daytime temperatures range from a comfortable 30°C (86°F) in July, the warmest time of the year, to a chilly 2°C (36°F) during cooler months like January.

At night, you can expect temperatures ranging from 19°C (66°F) in July to around -7°C (19°F) during January.

Check out our detailed temperature page for more information.

Temperature ranges by month

Decatur has a relatively rain/snowy climate with high precipitation levels, averaging 1057 mm (42 in) of rain/snowfall annually. Significant seasonal changes in precipitation occur throughout the year. In the wettest month, June it receives high rainfall, averaging 149 mm (5.9 in) of precipitation, recorded across 12 rainy days. In contrast, the driest month January brings less snow/rainfall, with 43 mm (1.7 in) over 8 snowy/rainy days. For more details, please visit our Decatur Precipitation page.

The mean monthly precipitation over the year, including rain, hail, and snow

The average number of days each month with precipitation

Seasonal changes in sunshine hours are quite dramatic in Decatur. While July receives considerable daily sunshine with up to 10.7 hours, December marks the darkest time of the year, where sunshine is scarce with only 4.3 hours of sunlight per day.

Visit our detailed sunshine hours page for more information.

Monthly hours of sunshine

Daily hours of sunshine

Daily percentage of sunshine

The relative humidity is high throughout the year in Decatur.

The city experiences its highest humidity in December, reaching 78%. In April, the humidity drops to its lowest level at 65%. What does this mean? Read our detailed page on humidity levels for further details.

Relative humidity over the year