Illinois · NWS LSX office

O'Fallon, IL weather

It is 50°F and clear at St. Louis Downtown Airport as of Oct 28, 12:25 AM CDT. Overnight: Mostly Clear, low near 51°F. Forecast from the National Weather Service, issued Oct 28, 12:56 AM CDT.

Updated Oct 28, 1:27 AM CDT (snapshot)

Current conditions

Temperature

50°F

Clear

Wind

S 3 mph

Humidity 94% · dew point 48°F

Pressure · visibility

30.20 inHg

Visibility 10 mi

Observed at St. Louis Downtown Airport (KCPS), Oct 28, 12:25 AM CDT. Station readings can lag or be missing.

Alerts for this area

No active NWS alerts cover the O'Fallon forecast zone right now.

Around the NWS LSX forecast area

No active alerts in zones served by the LSX office near O'Fallon.

From the alert snapshot of Oct 28, 2026, 2:15 AM EDT. No alerts are active anywhere in Illinois.

For official warnings, check weather.gov and your local authorities. OpenForecast repeats National Weather Service alerts and may be delayed or incomplete. Follow instructions from emergency officials.

Next 24 hours

Hourly forecast for O'Fallon (local time)
TimeTempForecastPrecip. chanceWind
Wed 1 AM54°FMostly Clear2%S 2 mph
Wed 2 AM53°FMostly Clear2%S 2 mph
Wed 3 AM53°FMostly Clear2%S 2 mph
Wed 4 AM52°FMostly Clear2%S 2 mph
Wed 5 AM51°FMostly Clear2%S 2 mph
Wed 6 AM51°FSunny2%S 2 mph
Wed 7 AM51°FSunny2%S 2 mph
Wed 8 AM52°FSunny2%S 3 mph
Wed 9 AM57°FSunny2%S 5 mph
Wed 10 AM65°FSunny2%S 5 mph
Wed 11 AM70°FSunny2%S 7 mph
Wed 12 PM74°FSunny3%S 8 mph
Wed 1 PM77°FSunny2%S 9 mph
Wed 2 PM78°FSunny0%S 9 mph
Wed 3 PM79°FSunny0%S 10 mph
Wed 4 PM80°FSunny2%S 10 mph
Wed 5 PM78°FSunny2%S 9 mph
Wed 6 PM75°FClear0%S 8 mph
Wed 7 PM70°FClear0%S 7 mph
Wed 8 PM64°FClear0%S 7 mph
Wed 9 PM62°FClear0%S 6 mph
Wed 10 PM61°FMostly Clear0%S 6 mph
Wed 11 PM60°FClear0%S 6 mph
Thu 12 AM59°FClear0%S 5 mph

Hourly values come from the NWS gridded forecast for the 2.5 km grid square that covers the city's center point. Conditions elsewhere in O'Fallon can differ.

7-day forecast

Overnight

Low 51°F

Mostly clear, with a low around 51. South wind around 2 mph.

Wednesday

High 78°F·Low 54°F

Sunny, with a high near 78. South wind 2 to 10 mph.

Wednesday Night: Clear, with a low around 54. South wind 5 to 8 mph.

Thursday

High 82°F·Low 56°F

Sunny, with a high near 82. Southwest wind around 7 mph.

Thursday Night: Partly cloudy, with a low around 56. Southeast wind around 3 mph.

Friday

High 79°F·Low 57°F

Partly sunny, with a high near 79.

Friday Night: Mostly cloudy, with a low around 57.

Saturday

High 72°F·Low 57°F

A slight chance of rain showers after 1pm. Mostly cloudy, with a high near 72. Chance of precipitation is 20%.

Saturday Night: Rain showers likely. Mostly cloudy, with a low around 57. Chance of precipitation is 60%.

Sunday

High 70°F·Low 57°F

A chance of rain showers. Mostly cloudy, with a high near 70. Chance of precipitation is 40%.

Sunday Night: A slight chance of rain showers after midnight. Mostly cloudy, with a low around 57. Chance of precipitation is 20%.

Monday

High 72°F·Low 57°F

A chance of rain showers before noon, then a chance of showers and thunderstorms. Mostly cloudy, with a high near 72. Chance of precipitation is 40%.

Monday Night: Rain showers likely. Mostly cloudy, with a low around 57. Chance of precipitation is 60%.

Tuesday

High 70°F

A chance of rain showers. Mostly cloudy, with a high near 70. Chance of precipitation is 50%.

Nearby cities

Larger cities in the area

Other cities in St. Clair County

See every city we cover in Illinois, or check all active alerts.

About this forecast

Forecast office
O'Fallon is served by the National Weather Service LSX forecast office, forecast zone ILZ101, county zone ILC163.
Location used
The Census Bureau's internal point for O'Fallon (38.6000, -89.9154), in St. Clair County. Population: 32,169 (2024 estimate), number 59 of the 121 Illinois cities on this site.
Radar
Nearest NWS radar: KLSX. View it on radar.weather.gov.

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Sources

  • Forecast, hourly forecast, observations and alerts: National Weather Service API, api.weather.gov/points/38.6,-89.9154 (forecast issued Oct 28, 12:56 AM CDT).
  • Official forecast page: forecast.weather.gov.
  • City location and population: U.S. Census Bureau, Vintage 2024 population estimates and 2024 Gazetteer files.
  • Snapshot taken Oct 28, 2026. The NWS and Census Bureau do not endorse OpenForecast.

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