Hourly Weather | Today Tuesday, July 21, 2026
Active Weather Warnings
O'Fallon, Missouri
4 AM
Stormy Weather
79°
Feels Like 82°
65
Humidity: 89%
UV Index: 0
Wind: 7 mph
5 AM
Cloudy Night
77°
Feels Like 84°
43
Humidity: 91%
UV Index: 0
Wind: 7 mph
6 AM
Sunny with a Chance of Thunderstorms
79°
Feels Like 82°
51
Humidity: 88%
UV Index: 0
Wind: 7 mph
7 AM
Cloudy Weather
79°
Feels Like 88°
47
Humidity: 84%
UV Index: 1
Wind: 8 mph
8 AM
Cloudy Weather
81°
Feels Like 90°
43
Humidity: 80%
UV Index: 2
Wind: 8 mph
9 AM
Cloudy Weather
84°
Feels Like 95°
47
Humidity: 75%
UV Index: 3
Wind: 8 mph
10 AM
Sunny with a Chance of Thunderstorms
86°
Feels Like 97°
51
Humidity: 72%
UV Index: 5
Wind: 9 mph
11 AM
Cloudy Weather
90°
Feels Like 102°
40
Humidity: 62%
UV Index: 7
Wind: 9 mph
12 PM
Cloudy Weather
91°
Feels Like 102°
34
Humidity: 54%
UV Index: 10
Wind: 9 mph
1 PM
Cloudy Weather
91°
Feels Like 102°
29
Humidity: 48%
UV Index: 11
Wind: 9 mph
2 PM
Cloudy Weather
93°
Feels Like 102°
20
Humidity: 44%
UV Index: 10
Wind: 9 mph
3 PM
Cloudy Weather
93°
Feels Like 100°
20
Humidity: 40%
UV Index: 7
Wind: 10 mph
4 PM
Cloudy Weather
93°
Feels Like 97°
20
Humidity: 41%
UV Index: 5
Wind: 10 mph
5 PM
Cloudy Weather
91°
Feels Like 93°
20
Humidity: 42%
UV Index: 3
Wind: 10 mph
6 PM
Cloudy Weather
90°
Feels Like 90°
20
Humidity: 46%
UV Index: 2
Wind: 10 mph
7 PM
Cloudy Weather
86°
Feels Like 88°
13
Humidity: 50%
UV Index: 1
Wind: 10 mph
8 PM
Cloudy Weather
84°
Feels Like 82°
0
Humidity: 55%
UV Index: 0
Wind: 9 mph
9 PM
Cloudy Night
81°
Feels Like 81°
0
Humidity: 62%
UV Index: 0
Wind: 7 mph
10 PM
Cloudy Night
79°
Feels Like 79°
0
Humidity: 68%
UV Index: 0
Wind: 7 mph
11 PM
Cloudy Night
75°
Feels Like 75°
0
Humidity: 73%
UV Index: 0
Wind: 7 mph

Hourly Air Quality Forecast - AQI (US EPA)

4 AM
14 AQI
Good air quality Dominant pollutant: O3
Details

Pollutant Concentrations:

  • PM2.5: 2.82 µg/m³
  • PM10: 3.43 µg/m³
  • O3: 0.015 ppm
  • NO2: 0.6 ppb
  • SO2: 0 ppb
  • CO: 0.08 ppm

Health Recommendations:

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

5 AM
16 AQI
Good air quality Dominant pollutant: O3
Details

Pollutant Concentrations:

  • PM2.5: 2.74 µg/m³
  • PM10: 3.4 µg/m³
  • O3: 0.018 ppm
  • NO2: 0.6 ppb
  • SO2: 0 ppb
  • CO: 0.08 ppm

Health Recommendations:

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

6 AM
17 AQI
Good air quality Dominant pollutant: O3
Details

Pollutant Concentrations:

  • PM2.5: 2.67 µg/m³
  • PM10: 3.33 µg/m³
  • O3: 0.018 ppm
  • NO2: 0.6 ppb
  • SO2: 0.1 ppb
  • CO: 0.08 ppm

Health Recommendations:

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

7 AM
17 AQI
Good air quality Dominant pollutant: O3
Details

Pollutant Concentrations:

  • PM2.5: 2.75 µg/m³
  • PM10: 3.4 µg/m³
  • O3: 0.019 ppm
  • NO2: 0.7 ppb
  • SO2: 0.1 ppb
  • CO: 0.09 ppm

Health Recommendations:

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

8 AM
18 AQI
Good air quality Dominant pollutant: O3
Details

Pollutant Concentrations:

  • PM2.5: 2.96 µg/m³
  • PM10: 3.59 µg/m³
  • O3: 0.019 ppm
  • NO2: 0.9 ppb
  • SO2: 0.1 ppb
  • CO: 0.09 ppm

Health Recommendations:

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

9 AM
19 AQI
Good air quality Dominant pollutant: O3
Details

Pollutant Concentrations:

  • PM2.5: 3.2 µg/m³
  • PM10: 3.82 µg/m³
  • O3: 0.021 ppm
  • NO2: 0.9 ppb
  • SO2: 0.2 ppb
  • CO: 0.09 ppm

Health Recommendations:

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

10 AM
24 AQI
Good air quality Dominant pollutant: O3
Details

Pollutant Concentrations:

  • PM2.5: 3.46 µg/m³
  • PM10: 4.08 µg/m³
  • O3: 0.026 ppm
  • NO2: 0.7 ppb
  • SO2: 0.2 ppb
  • CO: 0.09 ppm

Health Recommendations:

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

11 AM
34 AQI
Good air quality Dominant pollutant: O3
Details

Pollutant Concentrations:

  • PM2.5: 3.48 µg/m³
  • PM10: 4.09 µg/m³
  • O3: 0.037 ppm
  • NO2: 0.3 ppb
  • SO2: 0.4 ppb
  • CO: 0.09 ppm

Health Recommendations:

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

12 PM
36 AQI
Good air quality Dominant pollutant: O3
Details

Pollutant Concentrations:

  • PM2.5: 3.58 µg/m³
  • PM10: 4.17 µg/m³
  • O3: 0.038 ppm
  • NO2: 0.3 ppb
  • SO2: 0.5 ppb
  • CO: 0.09 ppm

Health Recommendations:

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

1 PM
36 AQI
Good air quality Dominant pollutant: O3
Details

Pollutant Concentrations:

  • PM2.5: 3.78 µg/m³
  • PM10: 4.34 µg/m³
  • O3: 0.039 ppm
  • NO2: 0.2 ppb
  • SO2: 0.4 ppb
  • CO: 0.09 ppm

Health Recommendations:

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

2 PM
36 AQI
Good air quality Dominant pollutant: O3
Details

Pollutant Concentrations:

  • PM2.5: 3.72 µg/m³
  • PM10: 4.22 µg/m³
  • O3: 0.039 ppm
  • NO2: 0.2 ppb
  • SO2: 0.4 ppb
  • CO: 0.09 ppm

Health Recommendations:

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

3 PM
36 AQI
Good air quality Dominant pollutant: O3
Details

Pollutant Concentrations:

  • PM2.5: 3.54 µg/m³
  • PM10: 3.97 µg/m³
  • O3: 0.039 ppm
  • NO2: 0.2 ppb
  • SO2: 0.3 ppb
  • CO: 0.09 ppm

Health Recommendations:

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

4 PM
36 AQI
Good air quality Dominant pollutant: O3
Details

Pollutant Concentrations:

  • PM2.5: 3.56 µg/m³
  • PM10: 3.93 µg/m³
  • O3: 0.039 ppm
  • NO2: 0.2 ppb
  • SO2: 0.2 ppb
  • CO: 0.09 ppm

Health Recommendations:

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

5 PM
38 AQI
Good air quality Dominant pollutant: O3
Details

Pollutant Concentrations:

  • PM2.5: 3.89 µg/m³
  • PM10: 4.22 µg/m³
  • O3: 0.041 ppm
  • NO2: 0.2 ppb
  • SO2: 0.2 ppb
  • CO: 0.09 ppm

Health Recommendations:

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

6 PM
39 AQI
Good air quality Dominant pollutant: O3
Details

Pollutant Concentrations:

  • PM2.5: 4.43 µg/m³
  • PM10: 4.72 µg/m³
  • O3: 0.042 ppm
  • NO2: 0.3 ppb
  • SO2: 0.2 ppb
  • CO: 0.10 ppm

Health Recommendations:

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

7 PM
40 AQI
Good air quality Dominant pollutant: O3
Details

Pollutant Concentrations:

  • PM2.5: 4.9 µg/m³
  • PM10: 5.14 µg/m³
  • O3: 0.043 ppm
  • NO2: 0.4 ppb
  • SO2: 0.2 ppb
  • CO: 0.10 ppm

Health Recommendations:

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

8 PM
39 AQI
Good air quality Dominant pollutant: O3
Details

Pollutant Concentrations:

  • PM2.5: 5.39 µg/m³
  • PM10: 5.57 µg/m³
  • O3: 0.043 ppm
  • NO2: 0.6 ppb
  • SO2: 0.2 ppb
  • CO: 0.10 ppm

Health Recommendations:

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

9 PM
37 AQI
Good air quality Dominant pollutant: O3
Details

Pollutant Concentrations:

  • PM2.5: 5.97 µg/m³
  • PM10: 6.11 µg/m³
  • O3: 0.040 ppm
  • NO2: 0.8 ppb
  • SO2: 0.2 ppb
  • CO: 0.11 ppm

Health Recommendations:

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

10 PM
36 AQI
Good air quality Dominant pollutant: O3
Details

Pollutant Concentrations:

  • PM2.5: 6.53 µg/m³
  • PM10: 6.64 µg/m³
  • O3: 0.039 ppm
  • NO2: 0.9 ppb
  • SO2: 0.2 ppb
  • CO: 0.11 ppm

Health Recommendations:

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

11 PM
34 AQI
Good air quality Dominant pollutant: O3
Details

Pollutant Concentrations:

  • PM2.5: 6.62 µg/m³
  • PM10: 6.71 µg/m³
  • O3: 0.036 ppm
  • NO2: 0.9 ppb
  • SO2: 0.2 ppb
  • CO: 0.11 ppm

Health Recommendations:

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

Weather Alerts and Warnings for O'Fallon

Moderate Expected Likely

Heat Advisory

Heat Advisory issued July 21 at 2:48AM CDT until July 21 at 7:00PM CDT by NWS St Louis MO
Jul 21, 2:48 AM Jul 21, 7:00 PM
WHAT: Heat index values of 100 to 110 degrees.

WHERE: Portions of south central and southwest Illinois and
central, east central, and southeast Missouri.

WHEN: Until 7 PM CDT this evening.

IMPACTS: Hot temperatures and high humidity may cause heat
illnesses.

ADDITIONAL DETAILS: This is the fourth straight day with heat
index values of 100 degrees or higher over parts of the area.
+ Read More
Drink plenty of fluids, stay in an air-conditioned room, stay out of the sun, and check up on relatives and neighbors. Young children and pets should never be left unattended in vehicles under any circumstances. Take extra precautions if you work or spend time outside. When possible reschedule strenuous activities to early morning or evening. Know the signs and symptoms of heat exhaustion and heat stroke. Wear lightweight and loose fitting clothing when possible. To reduce risk during outdoor work, the Occupational Safety and Health Administration recommends scheduling frequent rest breaks in shaded or air conditioned environments. Anyone overcome by heat should be moved to a cool and shaded location. Heat stroke is an emergency! Call 9 1 1.
Updated: Jul 21, 2:58 AM Source: NWS Alert