| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 29°F | 46°F | 37°F | 4.5" |
| February | 31°F | 49°F | 39°F | 3.7" |
| March | 41°F | 61°F | 50°F | 7.8" |
| April | 51°F | 72°F | 61°F | 7.9" |
| May | 60°F | 80°F | 69°F | 6.9" |
| June | 69°F | 90°F | 79°F | 6.4" |
| July | 70°F | 90°F | 79°F | 5.7" |
| August | 68°F | 89°F | 77°F | 4.3" |
| September | 60°F | 83°F | 70°F | 2.8" |
| October | 49°F | 73°F | 60°F | 4.4" |
| November | 39°F | 60°F | 49°F | 8.5" |
| December | 33°F | 49°F | 40°F | 8.2" |
| Index | Charleston | Missouri | National |
| Air quality index | 44 | 97 | 42 |
| Pollution index | 2,522,770 | 1,630,255 | 2,726,193 |
| Measurement | Total |
| Days measured | 364 |
| Days with good air quality | 261 |
| Days with moderate air quality | 103 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.060% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.002% |
| Lead | 0.030% |
| Mercury | 0.040% |
| City | Population | Air Quality Index | National Avg. |
| Matthews, MO | 635 | 26 | 48.0% |
| Cairo, IL | 1,884 | 44 | 12.0% |
| Anniston, MO | 222 | 44 | 12.0% |
| East Prairie, MO | 2,980 | 44 | 12.0% |
| Pinhook, MO | 0 | 44 | 12.0% |
| Charleston, MO | 5,478 | 44 | 12.0% |
| City | Population | Air Quality Index | National Avg. |
| Preston, ID | 5,477 | 44 | 12.0% |
| Somerdale, NJ | 5,479 | 51 | 2.0% |
| New Holland, PA | 5,479 | 45 | 10.0% |
| Cameron, TX | 5,476 | 42 | 16.0% |
| Orchard Homes, MT | 5,480 | 40 | 20.0% |
| Charleston, MO | 5,478 | 44 | 12.0% |
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