Today | Weather | Monday, September 21, 2026

Weather in St. Charles, Missouri

12:53 PM
Now
Cloudy Weather
72° F
Feels Like 73°
Precipitation 16 %
Wind 7 mph
UV Index (0 - 11+) 1
Humidity 84 %
Today
Cloudy Weather
Day 73°
Night 64°
Precipitation 25 %
Wind 7 mph
UV Index (0 - 11+) 1

St. Charles Weather Forecast Updated

24 minutes ago
Last updated on
Weather Forecast History
Last Year's Weather on This Day (September 21, 2025)
Sunny with a Chance of Thunderstorms

Day

90°

Night

68°

Wind

6 mph

UV Index

50

Precipitation

59 %

Air Quality in St. Charles

NOW
28 AQI
Good air quality Dominant pollutant: O3

Pollutant Concentrations:

PM2.5 4.54 µg/m³
PM10 4.6 µg/m³
O3 0.031 ppm
NO2 0.7 ppb
SO2 0.2 ppb
CO 0.12 ppm
NH3 0.15 µg/m³
NO 0.17 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)
PM2.54.54 µg/m³
PM104.6 µg/m³
O360.41 µg/m³
NO21.28 µg/m³
SO20.42 µg/m³
CO135.73 µg/m³
NH30.15 µg/m³
NO0.17 µg/m³