Today | Weather | Monday, April 27, 2026
Active Weather Warnings

Weather in O'Fallon, Missouri

01:49 PM
Now
Cloudy Weather
75° F
Feels Like 75°
Precipitation 49 %
Wind 20 mph
UV Index (0 - 11+) 2
Humidity 72 %
Today
Stormy Weather
Day 79°
Night 52°
Precipitation 96 %
Wind 17 mph
UV Index (0 - 11+) 2

O'Fallon Weather Forecast Updated

Last updated on

Air Quality in O'Fallon

NOW
21 AQI
Good air quality Dominant pollutant: O3

Pollutant Concentrations:

PM2.5 1.02 µg/m³
PM10 1.16 µg/m³
O3 0.023 ppm
NO2 0.2 ppb
SO2 0 ppb
CO 0.10 ppm
NH3 0.36 µg/m³
NO 0.1 µg/m³
PM2.5 – Fine particles <2.5μm
PM10 – Inhalable particles <10μm
O3 – Ozone
NO2 – Nitrogen dioxide
SO2 – Sulfur dioxide
CO – Carbon monoxide
NH3 – Ammonia
NO – Nitric oxide

Health Recommendations:

Air quality is considered satisfactory, and air pollution poses little or no risk.

Show raw pollutant concentrations (µg/m³)
PM2.51.02 µg/m³
PM101.16 µg/m³
O344.62 µg/m³
NO20.47 µg/m³
SO20.06 µg/m³
CO118.64 µg/m³
NH30.36 µg/m³
NO0.1 µg/m³

Weather Alerts and Warnings for O'Fallon

Severe Future Possible

Flood Watch

Flood Watch issued April 27 at 11:18AM CDT until April 27 at 9:00PM CDT by NWS St Louis MO
Apr 27, 11:18 AM Apr 27, 9:00 PM
WHAT: Flash flooding caused by excessive rainfall is possible.

WHERE: Portions of Illinois, including the following areas, Bond
IL, Calhoun IL, Clinton IL, Fayette IL, Greene IL, Jersey IL,
Macoupin IL, Madison IL, Marion IL, Monroe IL, Montgomery IL, Saint
Clair IL and Washington IL and Missouri, including the following
areas, Audrain MO, Boone MO, Callaway MO, Cole MO, Franklin MO,
Gasconade MO, Jefferson MO, Lincoln MO, Moniteau MO, Montgomery MO,
Osage MO, Pike MO, Saint Charles MO, Saint Louis City MO, Saint
Louis MO and Warren MO.

WHEN: Until 9 PM CDT this evening.

IMPACTS: Excessive runoff may result in flooding of rivers,
creeks, streams, and other low-lying and flood-prone locations.

ADDITIONAL DETAILS:
- Thunderstorms producing heavy rainfall moving over the same areas
will have the potential to produce flash flooding.
+ Read More
You should monitor later forecasts and be prepared to take action should Flash Flood Warnings be issued.
Updated: Apr 27, 12:20 PM Source: NWS Alert