O'Fallon, MO Weather & Climate Normals
O'Fallon's real weather, in one number
O'Fallon, MO scores 48/100 on this site's reading of NOAA's own 30-year normals: strongly seasonal. Comfortable weather is limited to a shorter window; summers, winters, or precipitation swing wide. 5 of the year's 12 months average between 55 and 75°F, the range this site counts as mild.
O'Fallon's hottest and coldest months
O'Fallon's hottest month is Jul, averaging 77°F; its coldest is Jan, averaging 30°F, a 47.1°F swing across the year, one of the widest gaps in this dataset.
Rain and snow in O'Fallon
O'Fallon averages 44.42in of precipitation a year across roughly 107 days with measurable rain or snow, and 13.5in of snow a year.
Where O'Fallon ranks
O'Fallon ranks 2297 of 4876 US cities in this dataset for comfort score, and 36 of 135 within MO. About 95,355 people live there.
If you need tomorrow's forecast, not the 30-year average
Everything above is a 30-year average from WELDON SPRING NWS, MO US, 5.9 miles from O'Fallon, not a prediction for any specific day.
More on how this is worked out
What a 30-year climate normal actually is · Why this uses the nearest NOAA station