| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 22°F | 35°F | 29°F | 3.1" |
| February | 22°F | 36°F | 29°F | 1.8" |
| March | 34°F | 49°F | 41°F | 8.5" |
| April | 43°F | 62°F | 52°F | 4.3" |
| May | 53°F | 72°F | 62°F | 7.9" |
| June | 62°F | 80°F | 71°F | 3.6" |
| July | 67°F | 83°F | 76°F | 9.5" |
| August | 65°F | 82°F | 74°F | 6.3" |
| September | 58°F | 76°F | 67°F | 7.6" |
| October | 47°F | 65°F | 56°F | 8.0" |
| November | 37°F | 52°F | 44°F | 5.7" |
| December | 27°F | 39°F | 33°F | 2.7" |
| Index | Portage | Indiana | National |
| Air quality index | 37 | 56 | 42 |
| Pollution index | 80,238,704 | 2,719,453 | 2,726,193 |
| Measurement | Total |
| Days measured | 364 |
| Days with good air quality | 305 |
| Days with moderate air quality | 55 |
| Days w/ poor A.Q. for sensitive groups | 4 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.760% |
| Benzene | 0.560% |
| Carbon Tetrachloride | 0.280% |
| Lead | 0.480% |
| Mercury | 0.480% |
| City | Population | Air Quality Index | National Avg. |
| Westville, IN | 5,822 | 37 | 26.0% |
| Dune Acres, IN | 258 | 37 | 26.0% |
| New Chicago, IN | 1,846 | 37 | 26.0% |
| Valparaiso, IN | 33,707 | 37 | 26.0% |
| Porter, IN | 4,835 | 37 | 26.0% |
| Portage, IN | 36,524 | 37 | 26.0% |
| City | Population | Air Quality Index | National Avg. |
| Lincoln Park, MI | 36,525 | 56 | 12.0% |
| Rome, GA | 36,518 | 44 | 12.0% |
| Penticton, BC | 36,498 | n/a | |
| Bartlesville, OK | 36,495 | 45 | 10.0% |
| Dunedin, FL | 36,480 | 43 | 14.0% |
| Portage, IN | 36,524 | 37 | 26.0% |
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