| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 15°F | 33°F | 22°F | 2.3" |
| February | 20°F | 39°F | 28°F | 3.1" |
| March | 34°F | 58°F | 44°F | 4.4" |
| April | 42°F | 65°F | 52°F | 10.1" |
| May | 55°F | 77°F | 65°F | 14.1" |
| June | 64°F | 85°F | 73°F | 6.4" |
| July | 67°F | 90°F | 78°F | 4.8" |
| August | 67°F | 87°F | 76°F | 9.9" |
| September | 58°F | 82°F | 68°F | 6.9" |
| October | 46°F | 69°F | 56°F | 8.1" |
| November | 31°F | 54°F | 40°F | 1.8" |
| December | 16°F | 34°F | 24°F | 2.8" |
| Index | Henderson | Iowa | National |
| Air quality index | 40 | 39 | 42 |
| Pollution index | 4,349,930 | 1,154,535 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 283 |
| Days with moderate air quality | 82 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.210% |
| Benzene | 0.040% |
| Carbon Tetrachloride | 0.004% |
| Lead | 0.100% |
| Mercury | 0.160% |
| City | Population | Air Quality Index | National Avg. |
| Emerson, IA | 462 | 40 | 20.0% |
| Silver City, IA | 320 | 40 | 20.0% |
| Mineola, IA | 220 | 40 | 20.0% |
| Carson, IA | 730 | 40 | 20.0% |
| Hastings, IA | 154 | 40 | 20.0% |
| Henderson, IA | 213 | 40 | 20.0% |
| City | Population | Air Quality Index | National Avg. |
| Nanwalek, AK | 213 | 31 | 38.0% |
| Sweet Water, AL | 213 | 36 | 28.0% |
| Ruth, CA | 213 | 42 | 16.0% |
| Westside, CA | 213 | 72 | 44.0% |
| Rye, CO | 213 | 20 | 60.0% |
| Henderson, IA | 213 | 40 | 20.0% |
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