| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 37°F | 54°F | 45°F | 8.1" |
| February | 35°F | 55°F | 44°F | 5.4" |
| March | 44°F | 67°F | 55°F | 5.9" |
| April | 49°F | 72°F | 59°F | 7.1" |
| May | 56°F | 82°F | 69°F | 2.9" |
| June | 66°F | 89°F | 77°F | 4.9" |
| July | 70°F | 89°F | 78°F | 7.2" |
| August | 72°F | 94°F | 82°F | 5.2" |
| September | 63°F | 88°F | 75°F | 7.8" |
| October | 51°F | 76°F | 63°F | 3.6" |
| November | 41°F | 65°F | 52°F | 8.0" |
| December | 35°F | 55°F | 44°F | 5.0" |
| Index | Decatur | Alabama | National |
| Air quality index | 41 | 37 | 42 |
| Pollution index | 6,960,530 | 3,012,339 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 306 |
| Days with moderate air quality | 59 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.100% |
| Carbon Tetrachloride | 0.060% |
| Lead | 0.030% |
| Mercury | 0.010% |
| City | Population | Air Quality Index | National Avg. |
| Hartselle, AL | 14,421 | 41 | 18.0% |
| Somerville, AL | 653 | 41 | 18.0% |
| Mooresville, AL | 87 | 41 | 18.0% |
| Hillsboro, AL | 590 | 41 | 18.0% |
| Athens, AL | 26,686 | 41 | 18.0% |
| Decatur, AL | 54,344 | 41 | 18.0% |
| City | Population | Air Quality Index | National Avg. |
| Rocky Mount, NC | 54,330 | 36 | 28.0% |
| Yucaipa, CA | 54,358 | 89 | 78.0% |
| Albany, OR | 54,442 | 28 | 44.0% |
| Westchester, FL | 54,470 | 41 | 18.0% |
| Colton, CA | 54,215 | 89 | 78.0% |
| Decatur, AL | 54,344 | 41 | 18.0% |
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