| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 8°F | 29°F | 18°F | 0.6" |
| February | 10°F | 34°F | 21°F | 0.9" |
| March | 24°F | 48°F | 35°F | 1.3" |
| April | 35°F | 62°F | 48°F | 3.0" |
| May | 45°F | 73°F | 59°F | 3.9" |
| June | 57°F | 82°F | 70°F | 5.2" |
| July | 61°F | 87°F | 75°F | 3.2" |
| August | 59°F | 84°F | 71°F | 4.4" |
| September | 51°F | 78°F | 64°F | 3.2" |
| October | 38°F | 64°F | 50°F | 3.1" |
| November | 24°F | 49°F | 36°F | 1.0" |
| December | 11°F | 32°F | 21°F | 1.4" |
| Index | Hartford | South Dakota | National |
| Air quality index | 36 | 36 | 42 |
| Pollution index | 2,464,570 | 345,623 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 321 |
| Days with moderate air quality | 43 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.000% |
| Benzene | 0.030% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.020% |
| Mercury | 0.001% |
| City | Population | Air Quality Index | National Avg. |
| Crooks, SD | 1,408 | 36 | 28.0% |
| Sioux Falls, SD | 180,927 | 36 | 28.0% |
| Montrose, SD | 551 | 36 | 28.0% |
| Dell Rapids, SD | 3,678 | 36 | 28.0% |
| Harrisburg, SD | 6,420 | 36 | 28.0% |
| Hartford, SD | 3,300 | 36 | 28.0% |
| City | Population | Air Quality Index | National Avg. |
| Heron Bay, GA | 3,300 | 52 | 4.0% |
| Water Valley, MS | 3,300 | 33 | 34.0% |
| Elma, WA | 3,299 | 20 | 60.0% |
| Pagedale, MO | 3,301 | 54 | 8.0% |
| Southampton, NY | 3,301 | 41 | 18.0% |
| Hartford, SD | 3,300 | 36 | 28.0% |
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