| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 25°F | 44°F | 33°F | 5.3" |
| February | 27°F | 47°F | 35°F | 4.6" |
| March | 37°F | 59°F | 47°F | 6.2" |
| April | 47°F | 69°F | 57°F | 9.5" |
| May | 55°F | 76°F | 65°F | 8.4" |
| June | 64°F | 86°F | 74°F | 6.1" |
| July | 67°F | 88°F | 77°F | 9.0" |
| August | 66°F | 87°F | 75°F | 9.8" |
| September | 58°F | 80°F | 68°F | 7.6" |
| October | 47°F | 69°F | 57°F | 7.0" |
| November | 37°F | 57°F | 46°F | 8.3" |
| December | 28°F | 45°F | 36°F | 4.6" |
| Index | Farmington | Missouri | National |
| Air quality index | 54 | 97 | 42 |
| Pollution index | 753,473 | 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 | 0.001% |
| Benzene | 0.010% |
| Carbon Tetrachloride | 0.001% |
| Lead | 0.020% |
| Mercury | 0.020% |
| City | Population | Air Quality Index | National Avg. |
| Irondale, MO | 575 | 54 | 8.0% |
| Terre du Lac, MO | 2,382 | 54 | 8.0% |
| Junction City, MO | 270 | 54 | 8.0% |
| Bonne Terre, MO | 7,037 | 54 | 8.0% |
| Desloge, MO | 4,901 | 54 | 8.0% |
| Farmington, MO | 18,792 | 54 | 8.0% |
| City | Population | Air Quality Index | National Avg. |
| Bellwood, IL | 18,799 | 55 | 10.0% |
| Jacksonville, IL | 18,784 | 40 | 20.0% |
| Madisonville, KY | 18,801 | 43 | 14.0% |
| Seminole, FL | 18,772 | 43 | 14.0% |
| Onalaska, WI | 18,814 | 35 | 30.0% |
| Farmington, MO | 18,792 | 54 | 8.0% |
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