| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 2°F | 26°F | 14°F | 0.6" |
| February | 5°F | 30°F | 17°F | 0.7" |
| March | 19°F | 45°F | 31°F | 0.9" |
| April | 31°F | 61°F | 45°F | 2.3" |
| May | 43°F | 72°F | 57°F | 3.5" |
| June | 53°F | 82°F | 68°F | 3.6" |
| July | 58°F | 88°F | 73°F | 3.7" |
| August | 55°F | 84°F | 69°F | 2.5" |
| September | 46°F | 78°F | 61°F | 2.1" |
| October | 34°F | 63°F | 47°F | 2.0" |
| November | 19°F | 47°F | 32°F | 0.6" |
| December | 6°F | 28°F | 17°F | 1.0" |
| Index | Mellette | South Dakota | National |
| Air quality index | 20 | 36 | 42 |
| Pollution index | 206,038 | 345,623 | 2,726,193 |
| Measurement | Total |
| Days measured | 122 |
| Days with good air quality | 112 |
| Days with moderate air quality | 10 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.000% |
| Benzene | 0.003% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.000% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Mansfield, SD | 91 | 20 | 60.0% |
| Chelsea, SD | 54 | 20 | 60.0% |
| Northville, SD | 155 | 20 | 60.0% |
| Ashton, SD | 91 | 20 | 60.0% |
| Stratford, SD | 42 | 20 | 60.0% |
| Mellette, SD | 191 | 20 | 60.0% |
| City | Population | Air Quality Index | National Avg. |
| Coffee Springs, AL | 191 | 35 | 30.0% |
| Vredenburgh, AL | 191 | 52 | 4.0% |
| Hackberry, AZ | 191 | 13 | 74.0% |
| Dixon, IA | 191 | 46 | 8.0% |
| Hanlontown, IA | 191 | 15 | 70.0% |
| Mellette, SD | 191 | 20 | 60.0% |
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