NWS, American, European side by side around O'Fallon and nearby towns.Live rain radar →
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Next 14 hours
consensus of the three models
7-day forecast
where the models agree, and where they split
O'Fallon, MO is at its warmest in Jul (average highs near 88°F) and coldest in Jan (lows around 27°F), with roughly 45 in of precipitation across the year. Below, compare what NWS, American, European forecast for O'Fallon right now, and see exactly where they disagree.
O'Fallon climate by month
average daytime high and overnight low across a typical year
Jan
42°
27°
Feb
53°
33°
Mar
58°
38°
Apr
69°
48°
May
79°
58°
Jun
87°
66°
Jul
88°
70°
Aug
86°
69°
Sep
81°
62°
Oct
71°
51°
Nov
57°
40°
Dec
48°
34°
Common questions
What's the weather in O'Fallon today?
On this page we show what NWS, American, European each forecast for O'Fallon today, side by side and updated live. When all three agree the forecast is reliable; when they split, we flag it so you know the day is genuinely less certain.
Will it rain in O'Fallon today or tomorrow?
Check the hourly strip and 7-day forecast above. We compare rain from NWS, American, European for O'Fallon and flag the days where the models disagree on whether showers actually arrive, which is exactly when a single app can catch you out.
Which forecast is most accurate for O'Fallon?
No single model is always right. NWS, American, European each run their own physics, so we line all three up: when they agree the O'Fallon forecast is reliable, and when they split you should expect surprises. See our tested US accuracy scoreboard for how the models compare.
What is the warmest month in O'Fallon?
Jul is typically the warmest month in O'Fallon, with average highs around 88°F.
How cold does O'Fallon get?
The coldest month in O'Fallon is Jan, when overnight lows average about 27°F.
How much rain does O'Fallon get?
O'Fallon sees roughly 45 in of precipitation a year, with Aug usually the wettest month.
The forecasts Americans check
The two biggest apps keep their model a secret, so we can't show their numbers, only link you to them. The National Weather Service is public, so its data sits right in the comparison above.