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O'Fallon, MO Weather & Growing Conditions

Local forecast, frost dates, hardiness zone and planting guidance for O'Fallon, a city in St. Charles County, Missouri.

Today
96°F
Partly Sunny
Partly sunny, with a high near 96. Heat index values as high as 100. Southwest wind 3 to 7 mph.

7-day forecast for O'Fallon

WhenTempForecastWindPrecip
Today 96°F Partly Sunny 3 to 7 mph SW 1%
Tonight 72°F Partly Cloudy 1 to 5 mph SW 4%
Sunday 90°F Chance Rain Showers then Slight Chance Showers And Thunderstorms 2 to 6 mph W 42%
Sunday Night 66°F Showers And Thunderstorms Likely 7 mph N 71%
Monday 76°F Showers And Thunderstorms Likely 8 mph NE 71%
Monday Night 59°F Chance Showers And Thunderstorms 8 mph NE 29%
Tuesday 69°F Slight Chance Rain Showers then Mostly Cloudy 10 mph N 20%
Tuesday Night 53°F Mostly Cloudy 5 to 8 mph N 3%
Wednesday 72°F Mostly Sunny 7 mph N 1%
Wednesday Night 55°F Partly Cloudy 2 to 6 mph N 0%
Thursday 75°F Mostly Sunny 2 to 6 mph N 3%
Thursday Night 57°F Partly Cloudy 5 mph NE 4%
Friday 76°F Partly Sunny 5 mph NE 8%
Friday Night 57°F Partly Cloudy 3 mph NE 6%

Forecast source: National Weather Service (api.weather.gov) for O'Fallon (38.785, -90.721). Updated through the day.

Growing snapshot for O'Fallon

Last spring frost
Apr 10
First fall frost
Oct 26
Growing season
199 days
Hardiness zone
6b

More local growing data for O'Fallon: nearby ZIP 63368 weather · frost dates · planting calendar · Missouri frost dates

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Climate data from the nearest NOAA station, Weldon Spring Nws, Mo (4.4 mi from O'Fallon). Frost dates are 1991–2020 averages, not a forecast. Page updated Sep 19, 2026.