| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 17°F | 31°F | 24°F | 1.7" |
| February | 17°F | 32°F | 24°F | 1.1" |
| March | 26°F | 44°F | 34°F | 1.9" |
| April | 37°F | 59°F | 47°F | 4.0" |
| May | 48°F | 71°F | 59°F | 3.4" |
| June | 58°F | 80°F | 68°F | 4.0" |
| July | 61°F | 83°F | 72°F | 3.1" |
| August | 60°F | 81°F | 70°F | 4.6" |
| September | 52°F | 75°F | 63°F | 2.9" |
| October | 42°F | 62°F | 52°F | 3.1" |
| November | 32°F | 49°F | 40°F | 2.1" |
| December | 23°F | 35°F | 29°F | 1.7" |
| Index | St. Charles | Michigan | National |
| Air quality index | 26 | 69 | 42 |
| Pollution index | 7,127,120 | 4,161,606 | 2,726,193 |
| Measurement | Total |
| Days measured | 316 |
| Days with good air quality | 288 |
| Days with moderate air quality | 28 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.160% |
| Benzene | 0.040% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.050% |
| Mercury | 0.140% |
| City | Population | Air Quality Index | National Avg. |
| Hemlock, MI | 1,081 | 26 | 48.0% |
| Zilwaukee, MI | 1,791 | 26 | 48.0% |
| Merrill, MI | 869 | 26 | 48.0% |
| Saginaw, MI | 50,125 | 26 | 48.0% |
| Buena Vista, MI | 6,653 | 26 | 48.0% |
| St. Charles, MI | 2,152 | 26 | 48.0% |
| City | Population | Air Quality Index | National Avg. |
| Oakland, MD | 2,152 | 36 | 28.0% |
| Morrisville, NY | 2,152 | 27 | 46.0% |
| Rainier, OR | 2,152 | 18 | 64.0% |
| Arnold, CA | 2,151 | 39 | 22.0% |
| Choctaw Lake, OH | 2,151 | 45 | 10.0% |
| St. Charles, MI | 2,152 | 26 | 48.0% |