| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 17°F | 33°F | 25°F | 2.2" |
| February | 17°F | 34°F | 25°F | 1.8" |
| March | 27°F | 47°F | 36°F | 2.2" |
| April | 37°F | 61°F | 48°F | 3.3" |
| May | 47°F | 72°F | 59°F | 3.8" |
| June | 57°F | 80°F | 69°F | 4.0" |
| July | 60°F | 83°F | 72°F | 3.7" |
| August | 59°F | 81°F | 70°F | 4.2" |
| September | 52°F | 75°F | 63°F | 3.0" |
| October | 42°F | 63°F | 52°F | 3.1" |
| November | 32°F | 50°F | 40°F | 2.3" |
| December | 23°F | 37°F | 30°F | 2.0" |
| Index | Napoleon | Michigan | National |
| Air quality index | 39 | 69 | 42 |
| Pollution index | 3,811,680 | 4,161,606 | 2,726,193 |
| Measurement | Total |
| Days measured | 358 |
| Days with good air quality | 286 |
| Days with moderate air quality | 72 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.004% |
| Benzene | 0.040% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.040% |
| Mercury | 0.002% |
| City | Population | Air Quality Index | National Avg. |
| Manchester, MI | 2,170 | 39 | 22.0% |
| Clinton, MI | 2,885 | 39 | 22.0% |
| Brooklyn, MI | 1,088 | 39 | 22.0% |
| Michigan Center, MI | 4,879 | 39 | 22.0% |
| Addison, MI | 633 | 39 | 22.0% |
| Napoleon, MI | 905 | 39 | 22.0% |
| City | Population | Air Quality Index | National Avg. |
| Ganado, AZ | 905 | 17 | 66.0% |
| Boyden, IA | 905 | 36 | 28.0% |
| Bird Island, MN | 905 | 32 | 36.0% |
| Kindred, ND | 905 | 33 | 34.0% |
| Genoa, NE | 905 | 19 | 62.0% |
| Napoleon, MI | 905 | 39 | 22.0% |
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