| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 22°F | 42°F | 30°F | 3.2" |
| February | 24°F | 45°F | 33°F | 4.1" |
| March | 37°F | 59°F | 46°F | 5.9" |
| April | 46°F | 68°F | 56°F | 9.3" |
| May | 55°F | 76°F | 65°F | 7.4" |
| June | 65°F | 86°F | 75°F | 9.6" |
| July | 69°F | 89°F | 78°F | 12.2" |
| August | 66°F | 88°F | 76°F | 9.2" |
| September | 58°F | 80°F | 68°F | 8.8" |
| October | 47°F | 69°F | 57°F | 8.6" |
| November | 36°F | 57°F | 46°F | 7.2" |
| December | 26°F | 44°F | 34°F | 6.6" |
| Index | Hartwell | Missouri | National |
| Air quality index | 47 | 97 | 42 |
| Pollution index | 1,664,220 | 1,630,255 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 210 |
| Days with moderate air quality | 154 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.090% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.001% |
| Lead | 0.020% |
| Mercury | 0.040% |
| City | Population | Air Quality Index | National Avg. |
| Clinton, MO | 8,792 | 47 | 6.0% |
| Garden City, MO | 1,506 | 47 | 6.0% |
| Urich, MO | 530 | 47 | 6.0% |
| Brownington, MO | 107 | 47 | 6.0% |
| La Due, MO | 80 | 47 | 6.0% |
| Hartwell, MO | 99 | 47 | 6.0% |
| City | Population | Air Quality Index | National Avg. |
| Cullomburg, AL | 99 | 36 | 28.0% |
| Faunsdale, AL | 99 | 35 | 30.0% |
| Black Springs, AR | 99 | 38 | 24.0% |
| Tumacacori-Carmen, AZ | 99 | 31 | 38.0% |
| Alleghany, CA | 99 | 44 | 12.0% |
| Hartwell, MO | 99 | 47 | 6.0% |
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