| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 20°F | 34°F | 27°F | 2.6" |
| February | 20°F | 35°F | 27°F | 1.8" |
| March | 28°F | 47°F | 37°F | 2.5" |
| April | 37°F | 60°F | 48°F | 4.0" |
| May | 47°F | 70°F | 58°F | 3.5" |
| June | 56°F | 79°F | 68°F | 3.3" |
| July | 61°F | 82°F | 72°F | 3.6" |
| August | 60°F | 81°F | 70°F | 4.8" |
| September | 53°F | 75°F | 63°F | 3.4" |
| October | 43°F | 63°F | 53°F | 5.5" |
| November | 33°F | 51°F | 42°F | 2.7" |
| December | 25°F | 39°F | 32°F | 2.5" |
| Index | Decatur | Michigan | National |
| Air quality index | 38 | 69 | 42 |
| Pollution index | 1,797,130 | 4,161,606 | 2,726,193 |
| Measurement | Total |
| Days measured | 362 |
| Days with good air quality | 312 |
| Days with moderate air quality | 50 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.001% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.002% |
| Lead | 0.002% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Vandalia, MI | 387 | 37 | 26.0% |
| Lawton, MI | 1,533 | 38 | 24.0% |
| Mattawan, MI | 2,567 | 38 | 24.0% |
| Paw Paw, MI | 3,416 | 38 | 24.0% |
| Marcellus, MI | 1,140 | 38 | 24.0% |
| Decatur, MI | 1,935 | 38 | 24.0% |
| City | Population | Air Quality Index | National Avg. |
| Salem city, AR | 1,935 | 45 | 10.0% |
| New Songhees 1A, BC | 1,935 | n/a | |
| Avoca, AR | 1,936 | 44 | 12.0% |
| Edmonton, KY | 1,936 | 43 | 14.0% |
| Langdon, ND | 1,936 | 33 | 34.0% |
| Decatur, MI | 1,935 | 38 | 24.0% |
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