| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 49°F | 68°F | 58°F | 5.5" |
| February | 54°F | 72°F | 62°F | 4.7" |
| March | 60°F | 76°F | 67°F | 3.3" |
| April | 66°F | 82°F | 73°F | 0.7" |
| May | 70°F | 86°F | 78°F | 2.9" |
| June | 76°F | 91°F | 83°F | 4.8" |
| July | 79°F | 92°F | 85°F | 10.7" |
| August | 78°F | 94°F | 85°F | 2.5" |
| September | 74°F | 91°F | 82°F | 4.5" |
| October | 67°F | 85°F | 75°F | 5.5" |
| November | 59°F | 78°F | 67°F | 10.6" |
| December | 52°F | 70°F | 60°F | 4.0" |
| Index | Portland | Texas | National |
| Air quality index | 42 | 52 | 42 |
| Pollution index | 11,617,000 | 2,009,300 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 262 |
| Days with moderate air quality | 102 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.140% |
| Carbon Tetrachloride | 0.230% |
| Lead | 0.020% |
| Mercury | 0.020% |
| City | Population | Air Quality Index | National Avg. |
| Aransas Pass, TX | 9,269 | 42 | 16.0% |
| Gregory, TX | 2,218 | 42 | 16.0% |
| Bayside, TX | 428 | 42 | 16.0% |
| Morgan Farm, TX | 400 | 42 | 16.0% |
| Taft Southwest, TX | 1,440 | 42 | 16.0% |
| Portland, TX | 17,807 | 42 | 16.0% |
| City | Population | Air Quality Index | National Avg. |
| Albert Lea, MN | 17,804 | 15 | 70.0% |
| Amsterdam, NY | 17,823 | 37 | 26.0% |
| El Dorado, AR | 17,826 | 35 | 30.0% |
| Colonia, NJ | 17,782 | 51 | 2.0% |
| West Columbia, SC | 17,782 | 43 | 14.0% |
| Portland, TX | 17,807 | 42 | 16.0% |
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