O'Fallon, IL Weather

The most pleasant months of the year for O'Fallon are May, September and October. In O'Fallon, there are 3 comfortable months with high temperatures in the range of 70-85°. July is the hottest month for O'Fallon with an average high temperature of 89.2°, which ranks it as one of the hottest places in Illinois. January is the snowiest month in O'Fallon with 3.8 inches of snow, and 4 months of the year have significant snowfall. July is the most humid month, though humidity is low for most of the year.

Today's Weather - O'Fallon, IL

73°F

Weather Highlights

Summer High: the July high is around 89 degrees
Winter Low: the January low is 22
Rain: averages 43 inches of rain a year
Snow: averages 12 inches of snow a year

BESTPLACES COMFORT INDEX

The annual BestPlaces Comfort Index for the O'Fallon area is 7.3 (10=best), which means it is more comfortable than most places in Illinois.

7.3 / 10

A higher score indicates a more comfortable year-round climate. The US average for the comfort index is 7.8. Our index is based on the total number of days annually within the comfort range of 70-80 degrees, and we also applied a penalty for days of excessive humidity.

Average Monthly High and Low (°F)

Hot, Freezing, Rainy, Snowy Days: O'Fallon

YOU SHOULD KNOW

Many people confuse weather and climate but they are different. Weather is the conditions of the atmosphere over a short period of time, and climate is how the atmosphere is over long periods of time.

Weather is how the atmosphere is behaving and its effects upon life and human activities. Weather can change from minute-to-minute. Most people think of weather in terms of temperature, humidity, precipitation, cloudiness, brightness, visibility, wind, and atmospheric pressure.

Climate is the description of the long-term pattern of weather in a place. Climate can mean the average weather for a particular region and time period taken over 30 years. Climate is the average of weather over time.