| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 12°F | 31°F | 21°F | 0.7" |
| February | 15°F | 35°F | 24°F | 0.6" |
| March | 29°F | 50°F | 38°F | 1.0" |
| April | 40°F | 64°F | 51°F | 1.2" |
| May | 50°F | 75°F | 62°F | 1.5" |
| June | 61°F | 84°F | 72°F | 1.9" |
| July | 63°F | 86°F | 74°F | 1.3" |
| August | 61°F | 83°F | 71°F | 2.2" |
| September | 53°F | 79°F | 65°F | 2.1" |
| October | 41°F | 67°F | 53°F | 1.6" |
| November | 30°F | 52°F | 39°F | 0.8" |
| December | 18°F | 37°F | 26°F | 0.9" |
| Index | Jefferson | Iowa | National |
| Air quality index | 37 | 39 | 42 |
| Pollution index | 517,691 | 1,154,535 | 2,726,193 |
| Measurement | Total |
| Days measured | 214 |
| Days with good air quality | 210 |
| Days with moderate air quality | 4 |
| Days w/ poor A.Q. for sensitive groups | |
| Days with unhealthy air quality |
| Pollutant | Total |
| Arsenic | 0.000% |
| Benzene | 0.010% |
| Carbon Tetrachloride | 0.001% |
| Lead | 0.002% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Bagley, IA | 303 | 37 | 26.0% |
| Beaver, IA | 67 | 37 | 26.0% |
| Dawson, IA | 152 | 37 | 26.0% |
| Ralston, IA | 98 | 37 | 26.0% |
| Bayard, IA | 332 | 37 | 26.0% |
| Jefferson, IA | 4,121 | 37 | 26.0% |
| City | Population | Air Quality Index | National Avg. |
| Burnham, IL | 4,121 | 55 | 10.0% |
| Roebling, NJ | 4,120 | 41 | 18.0% |
| Dewey-Humboldt, AZ | 4,123 | 43 | 14.0% |
| Northwest Harwich, MA | 4,123 | 36 | 28.0% |
| Broad Brook, CT | 4,118 | 41 | 18.0% |
| Jefferson, IA | 4,121 | 37 | 26.0% |
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