| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 23°F | 48°F | 34°F | 2.4" |
| February | 25°F | 51°F | 37°F | 2.1" |
| March | 36°F | 63°F | 48°F | 3.8" |
| April | 45°F | 71°F | 57°F | 5.2" |
| May | 54°F | 78°F | 65°F | 5.9" |
| June | 64°F | 87°F | 75°F | 4.7" |
| July | 68°F | 91°F | 79°F | 4.3" |
| August | 66°F | 90°F | 77°F | 4.0" |
| September | 58°F | 83°F | 69°F | 5.4" |
| October | 46°F | 72°F | 58°F | 4.0" |
| November | 35°F | 61°F | 47°F | 3.2" |
| December | 26°F | 48°F | 36°F | 3.0" |
| Index | Mount Vernon | Missouri | National |
| Air quality index | 39 | 97 | 42 |
| Pollution index | 504,674 | 1,630,255 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 322 |
| Days with moderate air quality | 43 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.001% |
| Benzene | 0.010% |
| Carbon Tetrachloride | 0.001% |
| Lead | 0.000% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Crane, MO | 1,470 | 18 | 64.0% |
| Freistatt, MO | 329 | 37 | 26.0% |
| Wentworth, MO | 107 | 37 | 26.0% |
| Stotts City, MO | 138 | 37 | 26.0% |
| La Russell, MO | 146 | 37 | 26.0% |
| Mount Vernon, MO | 4,490 | 39 | 22.0% |
| City | Population | Air Quality Index | National Avg. |
| Ligonier, IN | 4,489 | 37 | 26.0% |
| Scottsville, KY | 4,489 | 43 | 14.0% |
| Denton, MD | 4,488 | 36 | 28.0% |
| Mount Vernon, IA | 4,487 | 39 | 22.0% |
| La Vale, MD | 4,486 | 36 | 28.0% |
| Mount Vernon, MO | 4,490 | 39 | 22.0% |
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