| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 20°F | 34°F | 26°F | 2.9" |
| February | 27°F | 47°F | 36°F | 2.2" |
| March | 35°F | 56°F | 44°F | 8.3" |
| April | 45°F | 65°F | 54°F | 4.8" |
| May | 51°F | 73°F | 61°F | 6.4" |
| June | 63°F | 87°F | 75°F | 4.8" |
| July | 67°F | 88°F | 77°F | 8.0" |
| August | 62°F | 84°F | 72°F | 5.8" |
| September | 58°F | 81°F | 69°F | 9.2" |
| October | 46°F | 69°F | 56°F | 8.5" |
| November | 35°F | 56°F | 45°F | 4.1" |
| December | 21°F | 36°F | 28°F | 2.6" |
| Index | Cromwell | Iowa | National |
| Air quality index | 39 | 39 | 42 |
| Pollution index | 338,773 | 1,154,535 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 306 |
| Days with moderate air quality | 59 |
| 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 | 0.000% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Shannon City, IA | 108 | 39 | 22.0% |
| Macksburg, IA | 97 | 39 | 22.0% |
| Tingley, IA | 105 | 39 | 22.0% |
| Creston, IA | 7,754 | 39 | 22.0% |
| Orient, IA | 434 | 39 | 22.0% |
| Cromwell, IA | 72 | 39 | 22.0% |
| City | Population | Air Quality Index | National Avg. |
| New Blaine, AR | 72 | 36 | 28.0% |
| Seba Dalkai, AZ | 72 | 45 | 10.0% |
| Mabie, CA | 72 | 44 | 12.0% |
| Smeltertown, CO | 72 | 16 | 68.0% |
| Ranger, GA | 72 | 43 | 14.0% |
| Cromwell, IA | 72 | 39 | 22.0% |
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