Today | Weather | Monday, September 21, 2026

Weather in O'Fallon, Missouri

12:52 PM
Now
Cloudy Weather
72° F
Feels Like 73°
Precipitation 16 %
Wind 7 mph
UV Index (0 - 11+) 1
Humidity 81 %
Today
Cloudy Weather
Day 73°
Night 64°
Precipitation 25 %
Wind 7 mph
UV Index (0 - 11+) 1

O'Fallon Weather Forecast Updated

5 minutes ago
Last updated on
Weather Forecast History
Last Year's Weather on This Day (September 21, 2025)
Stormy Weather

Day

88°

Night

66°

Wind

5 mph

Precipitation

99 %

Air Quality in O'Fallon

NOW
25 AQI
Good air quality Dominant pollutant: O3

Pollutant Concentrations:

PM2.5 4.86 µg/m³
PM10 4.93 µg/m³
O3 0.028 ppm
NO2 0.8 ppb
SO2 0.2 ppb
CO 0.12 ppm
NH3 0.21 µg/m³
NO 0.2 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)
PM2.54.86 µg/m³
PM104.93 µg/m³
O354.05 µg/m³
NO21.49 µg/m³
SO20.44 µg/m³
CO141.41 µg/m³
NH30.21 µg/m³
NO0.2 µg/m³