| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 15°F | 36°F | 24°F | 1.5" |
| February | 15°F | 35°F | 24°F | 2.3" |
| March | 30°F | 51°F | 39°F | 3.5" |
| April | 41°F | 65°F | 52°F | 8.7" |
| May | 52°F | 74°F | 62°F | 7.1" |
| June | 62°F | 83°F | 72°F | 5.9" |
| July | 66°F | 87°F | 76°F | 7.3" |
| August | 63°F | 84°F | 72°F | 7.4" |
| September | 54°F | 77°F | 64°F | 10.8" |
| October | 43°F | 66°F | 53°F | 4.9" |
| November | 30°F | 50°F | 39°F | 4.4" |
| December | 22°F | 39°F | 30°F | 4.0" |
| Index | Humeston | Iowa | National |
| Air quality index | 39 | 39 | 42 |
| Pollution index | 376,148 | 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 | 0.001% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Corydon, IA | 1,659 | 39 | 22.0% |
| Millerton, IA | 125 | 39 | 22.0% |
| Osceola, IA | 5,160 | 39 | 22.0% |
| Leon, IA | 1,883 | 39 | 22.0% |
| Weldon, IA | 145 | 39 | 22.0% |
| Humeston, IA | 449 | 39 | 22.0% |
| City | Population | Air Quality Index | National Avg. |
| Seville, CA | 449 | 66 | 32.0% |
| Victor, CO | 449 | 16 | 68.0% |
| Houston, DE | 449 | 42 | 16.0% |
| Waveland, IN | 449 | 45 | 10.0% |
| Galien, MI | 449 | 39 | 22.0% |
| Humeston, IA | 449 | 39 | 22.0% |
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