| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 33°F | 54°F | 42°F | 6.1" |
| February | 36°F | 57°F | 45°F | 6.6" |
| March | 42°F | 63°F | 51°F | 8.6" |
| April | 53°F | 75°F | 63°F | 7.8" |
| May | 61°F | 82°F | 71°F | 8.3" |
| June | 70°F | 88°F | 78°F | 6.4" |
| July | 68°F | 88°F | 77°F | 5.9" |
| August | 70°F | 91°F | 79°F | 6.0" |
| September | 65°F | 89°F | 76°F | 13.1" |
| October | 55°F | 78°F | 66°F | 6.4" |
| November | 43°F | 64°F | 52°F | 2.4" |
| December | 38°F | 54°F | 45°F | 3.5" |
| Index | Duncan | Mississippi | National |
| Air quality index | 43 | 40 | 42 |
| Pollution index | 1,813,640 | 1,514,109 | 2,726,193 |
| Measurement | Total |
| Days measured | 364 |
| Days with good air quality | 270 |
| Days with moderate air quality | 94 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.001% |
| Benzene | 0.040% |
| Carbon Tetrachloride | 0.002% |
| Lead | 0.010% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Lyon, MS | 439 | 43 | 14.0% |
| Mound Bayou, MS | 1,695 | 43 | 14.0% |
| Alligator, MS | 229 | 43 | 14.0% |
| Shelby, MS | 1,666 | 43 | 14.0% |
| Gunnison, MS | 430 | 43 | 14.0% |
| Duncan, MS | 320 | 43 | 14.0% |
| City | Population | Air Quality Index | National Avg. |
| Sand City, CA | 320 | 37 | 26.0% |
| Limestone, FL | 320 | 36 | 28.0% |
| Epworth, GA | 320 | 1 | 98.0% |
| Silver City, IA | 320 | 40 | 20.0% |
| Ewing, IL | 320 | 43 | 14.0% |
| Duncan, MS | 320 | 43 | 14.0% |
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