| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 28°F | 46°F | 36°F | 4.7" |
| February | 31°F | 50°F | 40°F | 4.6" |
| March | 39°F | 60°F | 49°F | 5.7" |
| April | 48°F | 71°F | 59°F | 5.8" |
| May | 55°F | 76°F | 65°F | 4.4" |
| June | 62°F | 82°F | 72°F | 5.0" |
| July | 66°F | 84°F | 75°F | 6.8" |
| August | 65°F | 84°F | 74°F | 3.8" |
| September | 58°F | 79°F | 68°F | 4.1" |
| October | 47°F | 70°F | 58°F | 3.6" |
| November | 38°F | 59°F | 48°F | 4.8" |
| December | 33°F | 50°F | 41°F | 6.4" |
| Index | Decatur | Tennessee | National |
| Air quality index | 30 | 76 | 42 |
| Pollution index | 7,263,220 | 2,454,916 | 2,726,193 |
| Measurement | Total |
| Days measured | 357 |
| Days with good air quality | 316 |
| Days with moderate air quality | 41 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.240% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.003% |
| Lead | 0.080% |
| Mercury | 0.300% |
| City | Population | Air Quality Index | National Avg. |
| Dayton, TN | 7,357 | 1 | 98.0% |
| Riceville, TN | 771 | 30 | 40.0% |
| Athens, TN | 13,931 | 30 | 40.0% |
| Spring City, TN | 2,242 | 30 | 40.0% |
| Etowah, TN | 3,505 | 30 | 40.0% |
| Decatur, TN | 1,612 | 30 | 40.0% |
| City | Population | Air Quality Index | National Avg. |
| Saint-François-de-la-Rivière-du-Sud, QC | 1,612 | n/a | |
| Pine Valley, CA | 1,611 | 64 | 28.0% |
| New Buffalo, MI | 1,613 | 37 | 26.0% |
| Nescopeck, PA | 1,613 | 38 | 24.0% |
| Shiremanstown, PA | 1,611 | 44 | 12.0% |
| Decatur, TN | 1,612 | 30 | 40.0% |
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