| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 20°F | 33°F | 27°F | 1.2" |
| February | 22°F | 34°F | 28°F | 1.3" |
| March | 30°F | 48°F | 38°F | 5.9" |
| April | 38°F | 58°F | 47°F | 5.4" |
| May | 52°F | 72°F | 61°F | 4.9" |
| June | 59°F | 80°F | 69°F | 6.0" |
| July | 65°F | 87°F | 76°F | 6.0" |
| August | 61°F | 82°F | 71°F | 7.8" |
| September | 52°F | 72°F | 61°F | 6.1" |
| October | 42°F | 63°F | 51°F | 3.5" |
| November | 33°F | 50°F | 41°F | 4.7" |
| December | 26°F | 36°F | 31°F | 2.5" |
| Index | Portland | Michigan | National |
| Air quality index | 36 | 69 | 42 |
| Pollution index | 1,401,450 | 4,161,606 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 330 |
| Days with moderate air quality | 35 |
| 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 | 0.005% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Eagle, MI | 116 | 36 | 28.0% |
| Sunfield, MI | 676 | 36 | 28.0% |
| Westphalia, MI | 808 | 36 | 28.0% |
| Grand Ledge, MI | 7,860 | 36 | 28.0% |
| Wacousta, MI | 1,698 | 36 | 28.0% |
| Portland, MI | 3,931 | 36 | 28.0% |
| City | Population | Air Quality Index | National Avg. |
| Rumford, ME | 3,931 | 40 | 20.0% |
| Oracle, AZ | 3,932 | 47 | 6.0% |
| Skippack, PA | 3,928 | 51 | 2.0% |
| Potosi, TX | 3,928 | 33 | 34.0% |
| Presidio, TX | 3,928 | 47 | 6.0% |
| Portland, MI | 3,931 | 36 | 28.0% |
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