| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 23°F | 44°F | 32°F | 2.1" |
| February | 25°F | 46°F | 35°F | 1.8" |
| March | 36°F | 60°F | 47°F | 3.7" |
| April | 46°F | 71°F | 58°F | 5.3" |
| May | 55°F | 78°F | 66°F | 4.5" |
| June | 65°F | 87°F | 76°F | 4.8" |
| July | 68°F | 90°F | 79°F | 2.9" |
| August | 66°F | 89°F | 77°F | 3.4" |
| September | 58°F | 82°F | 69°F | 3.9" |
| October | 46°F | 70°F | 57°F | 3.0" |
| November | 36°F | 59°F | 46°F | 2.8" |
| December | 27°F | 45°F | 35°F | 3.1" |
| Index | O'Fallon | Missouri | National |
| Air quality index | 54 | 97 | 42 |
| Pollution index | 3,042,530 | 1,630,255 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 134 |
| Days with moderate air quality | 221 |
| Days w/ poor A.Q. for sensitive groups | 8 |
| Days with unhealthy air quality | 2 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.040% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.010% |
| Mercury | 0.001% |
| City | Population | Air Quality Index | National Avg. |
| Chain of Rocks, MO | 252 | 54 | 8.0% |
| Lake St. Louis, MO | 16,357 | 54 | 8.0% |
| Crystal Lake Park, MO | 440 | 54 | 8.0% |
| St. Peters, MO | 57,536 | 54 | 8.0% |
| Clarkson Valley, MO | 2,619 | 54 | 8.0% |
| O'Fallon, MO | 88,132 | 54 | 8.0% |
| City | Population | Air Quality Index | National Avg. |
| Palm Coast, FL | 88,222 | 31 | 38.0% |
| Champaign, IL | 88,288 | 42 | 16.0% |
| Newton, MA | 88,322 | 43 | 14.0% |
| Reading, PA | 88,333 | 42 | 16.0% |
| Conroe, TX | 88,369 | 52 | 4.0% |
| O'Fallon, MO | 88,132 | 54 | 8.0% |
Here are the best places to live in Missouri
Most Dangerous States In The US
These are the largest cities in Missouri
Check out the 10 most dangerous cities in Missouri