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
| When | Temp | Forecast | Wind | Precip |
|---|---|---|---|---|
| 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
Nearby towns & communities
Augusta
Cottleville
Dardenne Prairie
Defiance
Flint Hill
Foristell
Josephville
Lake St. Louis
New Melle
St. Paul
St. Peters
Weldon Spring
Weldon Spring Heights
Wentzville
West Alton
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.