| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 14°F | 30°F | 21°F | 1.4" |
| February | 17°F | 33°F | 24°F | 2.7" |
| March | 31°F | 50°F | 39°F | 3.7" |
| April | 40°F | 63°F | 50°F | 7.2" |
| May | 52°F | 74°F | 62°F | 7.7" |
| June | 62°F | 82°F | 72°F | 7.8" |
| July | 65°F | 85°F | 74°F | 7.6" |
| August | 63°F | 82°F | 72°F | 7.4" |
| September | 54°F | 77°F | 64°F | 7.1" |
| October | 43°F | 64°F | 53°F | 6.9" |
| November | 32°F | 50°F | 40°F | 3.7" |
| December | 20°F | 35°F | 27°F | 5.3" |
| Index | Montezuma | Iowa | National |
| Air quality index | 39 | 39 | 42 |
| Pollution index | 684,464 | 1,154,535 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 287 |
| Days with moderate air quality | 78 |
| 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 | 0.001% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Gibson, IA | 30 | 35 | 30.0% |
| What Cheer, IA | 715 | 35 | 30.0% |
| Keswick, IA | 295 | 35 | 30.0% |
| Barnes City, IA | 147 | 35 | 30.0% |
| Thornburg, IA | 55 | 35 | 30.0% |
| Montezuma, IA | 1,490 | 39 | 22.0% |
| City | Population | Air Quality Index | National Avg. |
| Bement, IL | 1,490 | 44 | 12.0% |
| Saint-Malachie, QC | 1,490 | n/a | |
| Pierson, FL | 1,491 | 31 | 38.0% |
| Herscher, IL | 1,489 | 0 | 100.0% |
| Ness City, KS | 1,489 | 15 | 70.0% |
| Montezuma, IA | 1,490 | 39 | 22.0% |
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