| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 13°F | 31°F | 21°F | 2.9" |
| February | 15°F | 33°F | 23°F | 2.6" |
| March | 29°F | 49°F | 38°F | 4.2" |
| April | 39°F | 62°F | 50°F | 6.5" |
| May | 51°F | 74°F | 61°F | 6.2" |
| June | 61°F | 82°F | 71°F | 7.9" |
| July | 64°F | 84°F | 73°F | 6.6" |
| August | 61°F | 82°F | 71°F | 9.8" |
| September | 53°F | 76°F | 64°F | 6.2" |
| October | 42°F | 64°F | 52°F | 6.1" |
| November | 30°F | 50°F | 39°F | 4.3" |
| December | 19°F | 34°F | 26°F | 4.0" |
| Index | DeWitt | Iowa | National |
| Air quality index | 42 | 39 | 42 |
| Pollution index | 1,592,910 | 1,154,535 | 2,726,193 |
| Measurement | Total |
| Days measured | 364 |
| Days with good air quality | 268 |
| Days with moderate air quality | 96 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.090% |
| Benzene | 0.030% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.010% |
| Mercury | 0.010% |
| City | Population | Air Quality Index | National Avg. |
| Camanche, IA | 4,342 | 42 | 16.0% |
| Princeton, IA | 942 | 42 | 16.0% |
| Charlotte, IA | 378 | 42 | 16.0% |
| Goose Lake, IA | 298 | 42 | 16.0% |
| Cordova, IL | 685 | 42 | 16.0% |
| DeWitt, IA | 5,215 | 42 | 16.0% |
| City | Population | Air Quality Index | National Avg. |
| Deer Lake, NL | 5,214 | n/a | |
| Ranson, WV | 5,217 | 38 | 24.0% |
| McGregor, TX | 5,212 | 38 | 24.0% |
| Brewton, AL | 5,210 | 41 | 18.0% |
| Anthony, TX | 5,210 | 53 | 6.0% |
| DeWitt, IA | 5,215 | 42 | 16.0% |
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