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.
Tonight
73°F
Slight Chance Showers And Thunderstorms then Mostly Clear
A slight chance of showers and thunderstorms before 8pm. Mostly clear, with a low around 73. Southeast wind around 3 mph. Chance of precipitation is 20%.
7-day forecast for O'Fallon
| When | Temp | Forecast | Wind | Precip |
|---|---|---|---|---|
| Tonight | 73°F | Slight Chance Showers And Thunderstorms then Mostly Clear | 3 mph SE | 17% |
| Saturday | 96°F | Partly Sunny | 3 to 7 mph SW | 5% |
| Saturday Night | 72°F | Partly Cloudy | 1 to 5 mph SW | 5% |
| Sunday | 91°F | Chance Rain Showers then Chance Showers And Thunderstorms | 5 mph W | 31% |
| Sunday Night | 66°F | Chance Showers And Thunderstorms then Showers And Thunderstorms Likely | 6 mph N | 66% |
| Monday | 77°F | Showers And Thunderstorms Likely | 7 mph N | 69% |
| Monday Night | 59°F | Showers And Thunderstorms Likely | 8 mph N | 66% |
| Tuesday | 70°F | Slight Chance Rain Showers then Mostly Cloudy | 9 mph N | 23% |
| Tuesday Night | 54°F | Mostly Cloudy | 5 to 8 mph N | 5% |
| Wednesday | 73°F | Mostly Sunny | 6 mph N | 0% |
| Wednesday Night | 55°F | Partly Cloudy | 5 mph N | 1% |
| Thursday | 74°F | Mostly Sunny | 5 mph N | 3% |
| Thursday Night | 57°F | Partly Cloudy | 3 mph NE | 3% |
| Friday | 75°F | Mostly Sunny | 5 mph NE | 8% |
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.