| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 20°F | 34°F | 27°F | 5.1" |
| February | 17°F | 32°F | 24°F | 2.5" |
| March | 28°F | 48°F | 37°F | 2.2" |
| April | 38°F | 62°F | 50°F | 2.7" |
| May | 49°F | 73°F | 61°F | 4.9" |
| June | 62°F | 84°F | 73°F | 9.1" |
| July | 61°F | 86°F | 73°F | 7.0" |
| August | 63°F | 84°F | 73°F | 8.3" |
| September | 55°F | 79°F | 67°F | 3.0" |
| October | 46°F | 67°F | 56°F | 4.5" |
| November | 33°F | 50°F | 41°F | 3.3" |
| December | 22°F | 32°F | 28°F | 2.2" |
| Index | Portage | 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. |
| Eastwood, MI | 5,675 | 38 | 24.0% |
| Parchment, MI | 1,887 | 38 | 24.0% |
| Lawton, MI | 1,533 | 38 | 24.0% |
| Mendon, MI | 835 | 38 | 24.0% |
| Augusta, MI | 842 | 38 | 24.0% |
| Portage, MI | 49,224 | 38 | 24.0% |
| City | Population | Air Quality Index | National Avg. |
| Harrisburg, PA | 49,247 | 44 | 12.0% |
| Troy, NY | 49,253 | 37 | 26.0% |
| Cuyahoga Falls, OH | 49,191 | 43 | 14.0% |
| Downers Grove, IL | 49,263 | 55 | 10.0% |
| Bedford, TX | 49,145 | 51 | 2.0% |
| Portage, MI | 49,224 | 38 | 24.0% |
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