Warm
Average highs sit around 30°C, giving warm days by monthly-average standards.
Weather Guide
O'Fallon, Illinois, United States Average Monthly Weather
Weather score53Mixed annual avg
Best months: August, June, July
Across the year, average daytime temperatures are around 18°C, sunshine averages 7.1h per day, and rainfall totals about 944mm.
Annual weather
Annual averages
Temp
18°C
Rain
944mm
Annual total
Sun
7.1h
Weather score
53
Mixed avg
Seasonal climate calendar
TemperatureTemp
RainRain
SunSun
Weather scoreWeather score
Trip feel
Drier
Rainfall averages 79mm, which is relatively low for holiday planning.
Bright
Sunshine averages 9h per day, so bright days are a strong part of the month.
Map
Weather map
Compare O'Fallon, Illinois, United States with nearby places by weather score, rain, sun, temperature, and swim conditions.
Temperature
August30°C average high
August is one of O'Fallon's warmest months, with daytime heat above the yearly average.
Warmest monthsMay to September
This stretch sets the upper range for average daytime heat.
Rain
August79mm average rain
August sits near O'Fallon's yearly rainfall average, so rain is a normal planning factor rather than an outlier.
Driest monthsJanuary to February and October to December
This is the drier part of the year, when outdoor plans usually need less weather flexibility.
Sun
August9 hours average sun
August is brighter than O'Fallon's yearly average, though the strongest sunshine usually sits closer to the peak months.
Brightest monthsMay to August
This stretch has the strongest sunshine in the monthly averages.
Weather score
August83 weather score
August is one of O'Fallon's best weather-score months, combining the strongest overall balance in the yearly averages.
Best weather monthsJune to September
These months have the strongest weather score in the monthly averages.
