2025 Compare Climate & Weather:
Naperville, IL vs O'Fallon, MO

Highlights

On average, there are 200 sunny days per year in O'Fallon. Naperville averages 189 sunny days per year. The US average is 205 sunny days.

O'Fallon, Missouri gets 42.7 inches of rain, on average, per year. Naperville, Illinois gets 38.6 inches of rain, on average, per year. The US average is 38.1 inches of rain per year.

O'Fallon averages 13.4 inches of snow per year. Naperville averages 28.7 inches of snow per year. The US average is 27.8 inches of snow per year.

Weather Highlights

O'Fallon, Missouri
Summer High: the July high is around 88 degrees
Winter Low: the January low is 20.7
Rain: averages 42.7 inches of rain a year
Snow: averages 13.4 inches of snow a year

Naperville, Illinois
Summer High: the July high is around 83.8 degrees
Winter Low: the January low is 15.1
Rain: averages 38.6 inches of rain a year
Snow: averages 28.7 inches of snow a year

BestPlaces Comfort Index

The annual BestPlaces Comfort Index for O'Fallon is 7.2 (10=best), which means it is more comfortable than most places in Missouri.

The annual BestPlaces Comfort Index for Naperville is 6.9 (10=best), which means it is less comfortable than most places in Illinois.

Today's Weather - Naperville, IL

61°F

Today's Weather - O'Fallon, MO

60°F

Average Monthly High / Low (°F)

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

July is the hottest month for Naperville with an average high temperature of 83.8°, which ranks it as cooler than most places in Illinois. In Naperville, there are 5 comfortable months with high temperatures in the range of 70-85°. The most pleasant months of the year for Naperville are June, September and August.

July is the hottest month for O'Fallon with an average high temperature of 88.0°, which ranks it as about average compared to other places in Missouri. In O'Fallon, there are 3 comfortable months with high temperatures in the range of 70-85°. The most pleasant months of the year for O'Fallon are September, May and June.

January has the coldest nighttime temperatures for Naperville with an average of 15.1°. This is colder than most places in Illinois.

January has the coldest nighttime temperatures for O'Fallon with an average of 20.7°. This is about average compared to other places in Missouri.

In Naperville, there are 8.6 days annually when the high temperature is over 90°, which is one of the coolest places in Illinois.

In O'Fallon, there are 32.2 days annually when the high temperature is over 90°, which is about average compared to other places in Missouri.

In Naperville, there are 135.4 days annually when the nighttime low temperature falls below freezing, which is colder than most places in Illinois.

In O'Fallon, there are 104.1 days annually when the nighttime low temperature falls below freezing, which is about average compared to other places in Missouri.

In Naperville, there are 6.1 days annually when the nighttime low temperature falls below zero°, which is about average compared to other places in Illinois.

In O'Fallon, there are 3.1 days annually when the nighttime low temperature falls below zero°, which is about average compared to other places in Missouri.

August is the wettest month in Naperville with 4.2 inches of rain, and the driest month is January with 1.9 inches. The wettest season is Autumn with 32% of yearly precipitation and 16% occurs in Spring, which is the driest season. The annual rainfall of 38.6 inches in Naperville means that it is about average compared to other places in Illinois.


May is the wettest month in O'Fallon with 4.9 inches of rain, and the driest month is January with 2.4 inches. The wettest season is Summer with 29% of yearly precipitation and 19% occurs in Spring, which is the driest season. The annual rainfall of 42.7 inches in O'Fallon means that it is drier than most places in Missouri.

May is the rainiest month in Naperville with 12.0 days of rain, and September is the driest month with only 7.9 rainy days. There are 120.3 rainy days annually in Naperville, which is rainier than most places in Illinois. The rainiest season is Summer when it rains 28% of the time and the driest is Winter with only a 22% chance of a rainy day.

May is the rainiest month in O'Fallon with 11.6 days of rain, and January is the driest month with only 7.2 rainy days. There are 106.5 rainy days annually in O'Fallon, which is one of the rainiest places in Missouri. The rainiest season is Summer when it rains 30% of the time and the driest is Spring with only a 22% chance of a rainy day.

An annual snowfall of 28.7 inches in Naperville means that it is snowier than most places in Illinois.

An annual snowfall of 13.4 inches in O'Fallon means that it is about average compared to other places in Missouri.

January is the snowiest month in Naperville with 9.1 inches of snow, and 6 months of the year have significant snowfall.

February is the snowiest month in O'Fallon with 4.5 inches of snow, and 5 months of the year have significant snowfall.