| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 17°F | 34°F | 25°F | 0.7" |
| February | 18°F | 36°F | 26°F | 2.1" |
| March | 33°F | 53°F | 41°F | 4.1" |
| April | 43°F | 66°F | 53°F | 4.8" |
| May | 53°F | 75°F | 63°F | 6.2" |
| June | 63°F | 84°F | 73°F | 5.9" |
| July | 65°F | 86°F | 75°F | 5.6" |
| August | 63°F | 84°F | 73°F | 2.0" |
| September | 55°F | 79°F | 65°F | 4.1" |
| October | 44°F | 66°F | 54°F | 6.1" |
| November | 33°F | 51°F | 41°F | 3.3" |
| December | 22°F | 38°F | 30°F | 3.1" |
| Index | Franklin | Iowa | National |
| Air quality index | 29 | 39 | 50 |
| Pollution index | 464,333 | 1,643,836 | 5,066,862 |
| Measurement | Total |
| Days measured | 120 |
| Days with good air quality | 101 |
| Days with moderate air quality | 19 |
| 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 | 0.320% |
| Mercury | 0.000% |
| City, State | Population | Air Quality Index | National Avg. |
| Hillsboro, IA | 228 | 29 | 42% |
| Salem, IA | 551 | 29 | 42% |
| Fort Madison, IA | 10,769 | 29 | 42% |
| Danville, IA | 1,079 | 29 | 42% |
| Houghton, IA | 152 | 29 | 42% |
| Franklin, IA | 110 | 29 | 42% |
| City, State | Population | Air Quality Index | National Avg. |
| Mount Hermon, NJ | 110 | 34 | 32% |
| Valmy, NV | 110 | 14 | 72% |
| New Weston, OH | 110 | 6 | 88% |
| Gem, KS | 110 | 19 | 62% |
| Tuskahoma, OK | 110 | 43 | 14% |
| Franklin, IA | 110 | 29 | 42% |
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