| 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 | 50 |
| Pollution index | 376,148 | 1,643,836 | 5,066,862 |
| 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, State | Population | Air Quality Index | National Avg. |
| Leon, IA | 1,995 | 39 | 22% |
| Weldon, IA | 181 | 39 | 22% |
| Chariton, IA | 4,219 | 39 | 22% |
| Garden Grove, IA | 183 | 39 | 22% |
| Derby, IA | 133 | 39 | 22% |
| Humeston, IA | 400 | 39 | 22% |
| City, State | Population | Air Quality Index | National Avg. |
| Amber, OK | 400 | 48 | 4% |
| Aneth, UT | 400 | 49 | 2% |
| Promised Land, SC | 400 | 31 | 38% |
| Manlius, IL | 400 | 42 | 16% |
| Mitchellville, AR | 400 | 43 | 14% |
| Humeston, IA | 400 | 39 | 22% |
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