| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 35°F | 61°F | 46°F | 5.5" |
| February | 36°F | 64°F | 49°F | 6.1" |
| March | 43°F | 73°F | 57°F | 6.3" |
| April | 50°F | 80°F | 65°F | 5.3" |
| May | 58°F | 85°F | 71°F | 4.3" |
| June | 67°F | 92°F | 79°F | 4.0" |
| July | 70°F | 93°F | 80°F | 5.3" |
| August | 70°F | 93°F | 80°F | 4.6" |
| September | 63°F | 89°F | 75°F | 3.0" |
| October | 50°F | 80°F | 64°F | 3.0" |
| November | 40°F | 71°F | 54°F | 3.6" |
| December | 37°F | 63°F | 49°F | 6.3" |
| Index | Decatur | Mississippi | National |
| Air quality index | 36 | 40 | 42 |
| Pollution index | 811,660 | 1,514,109 | 2,726,193 |
| Measurement | Total |
| Days measured | 245 |
| Days with good air quality | 229 |
| Days with moderate air quality | 16 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.000% |
| Benzene | 0.010% |
| Carbon Tetrachloride | 0.001% |
| Lead | 0.010% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Hickory, MS | 463 | 36 | 28.0% |
| Union, MS | 2,581 | 36 | 28.0% |
| Lake, MS | 507 | 36 | 28.0% |
| Chunky, MS | 255 | 36 | 28.0% |
| Newton, MS | 3,190 | 36 | 28.0% |
| Decatur, MS | 1,755 | 36 | 28.0% |
| City | Population | Air Quality Index | National Avg. |
| Kaibito, AZ | 1,755 | 45 | 10.0% |
| Portola, CA | 1,755 | 44 | 12.0% |
| Prudenville, MI | 1,755 | 36 | 28.0% |
| Corvallis, MT | 1,755 | 40 | 20.0% |
| Mercer, PA | 1,755 | 31 | 38.0% |
| Decatur, MS | 1,755 | 36 | 28.0% |
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