| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 14°F | 35°F | 23°F | 0.9" |
| February | 17°F | 39°F | 26°F | 1.2" |
| March | 30°F | 54°F | 41°F | 2.2" |
| April | 41°F | 67°F | 53°F | 4.9" |
| May | 51°F | 76°F | 63°F | 4.9" |
| June | 62°F | 86°F | 74°F | 6.5" |
| July | 66°F | 89°F | 77°F | 4.2" |
| August | 64°F | 87°F | 75°F | 5.1" |
| September | 56°F | 81°F | 68°F | 3.7" |
| October | 43°F | 68°F | 55°F | 3.2" |
| November | 31°F | 54°F | 42°F | 1.8" |
| December | 18°F | 38°F | 27°F | 2.1" |
| Index | Hartford | Iowa | National |
| Air quality index | 39 | 39 | 42 |
| Pollution index | 9,310,160 | 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 | 0.010% |
| Benzene | 0.110% |
| Carbon Tetrachloride | 0.080% |
| Lead | 0.030% |
| Mercury | 0.010% |
| City | Population | Air Quality Index | National Avg. |
| Mitchellville, IA | 2,382 | 39 | 22.0% |
| Runnells, IA | 485 | 39 | 22.0% |
| Sandyville, IA | 64 | 39 | 22.0% |
| Altoona, IA | 18,917 | 39 | 22.0% |
| Milo, IA | 781 | 39 | 22.0% |
| Hartford, IA | 709 | 39 | 22.0% |
| City | Population | Air Quality Index | National Avg. |
| Two Rivers, AK | 709 | 38 | 24.0% |
| Onaga, KS | 709 | 32 | 36.0% |
| Conway, MO | 709 | 39 | 22.0% |
| Silver Springs, NY | 709 | 37 | 26.0% |
| Welling, OK | 709 | 36 | 28.0% |
| Hartford, IA | 709 | 39 | 22.0% |
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