See exactly when rain will start and stop with a minute-by-minute precipitation nowcast for the next hour.
36°
Mostly Cloudy
Feels Like: 39°
Min: 24°
Max: 37°
The next few hours will be clear, with today reaching 37°C and dropping to 24°C. The coming days will be partly cloudy throughout the day.
Compare today's weather with yesterday's data and track temperature trends over time.
Hourly Forecast
Daylight Hours
06:50
Sunrise
19:04
Sunset
Moon
Waxing Crescent
11:35
Moonrise
20:43
Moonset
Daily Forecast
Today
Wednesday
Thursday
Friday
Saturday
Sunday
Monday
Tuesday
Wednesday
Thursday
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Weather in O'Fallon today, September 15, 2026
O'Fallon starts September 15, 2026 looking damp, with rain in the forecast and wetter spells likely at times. Waterproof kit is the safer call for early plans.
Expect highs of 37°C and cooler readings close to 24°C. Relative humidity sits between 39% and 86%, reaching its peak around 23:00. Winds stay light, near 9.2 km/h by 18:00, so the day feels still more than breezy.
Expect persistent cloud later on, with amounts around 100% by 17:00. Sunshine remains the exception, not the rule. Visibility stays generally good near 13.2 km on average, though it can drop toward 3.3 km in thicker cloud or showers. The sun rises at 06:50 and sets at 19:04, for a total of 12 hours 14 minutes of sunlight today.
Taken together, O'Fallon looks wet enough on September 15, 2026 that flexible outdoor plans work best, with temperatures peaking near 37°C.
Frequently asked questions about weather in O'Fallon
How warm does it get in O'Fallon?
The warmest month in O'Fallon is July, with average high temperatures of 31°C. The average temperature during this period is around 26°C.
How cold does it get in O'Fallon?
The coldest month in O'Fallon is January, with average low temperatures of -3°C. The average temperature during this period is around 0°C.
What is the wettest time of year in O'Fallon?
The wettest month in O'Fallon is May, with an average of 130mm of precipitation.
What is the driest time of year in O'Fallon?
The driest month in O'Fallon is December, with an average of 52mm of precipitation.
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