| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 34°F | 48°F | 40°F | 4.9" |
| February | 36°F | 53°F | 43°F | 3.4" |
| March | 39°F | 58°F | 48°F | 4.8" |
| April | 42°F | 63°F | 52°F | 3.0" |
| May | 48°F | 71°F | 58°F | 2.8" |
| June | 53°F | 76°F | 63°F | 1.7" |
| July | 57°F | 84°F | 69°F | 0.5" |
| August | 58°F | 85°F | 70°F | 0.5" |
| September | 53°F | 78°F | 64°F | 1.8" |
| October | 47°F | 66°F | 55°F | 3.7" |
| November | 40°F | 55°F | 47°F | 6.2" |
| December | 34°F | 47°F | 40°F | 6.2" |
| Index | Centennial | Portland | Oregon |
| Air quality index | 38 | 38 | 32 |
| Pollution index | 24,235,400 | 1,899,410 | 7,156,356 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 285 |
| Days with moderate air quality | 77 |
| Days w/ poor A.Q. for sensitive groups | 3 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.003% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.010% |
| Mercury | 0.002% |
| City | Population | Air Quality Index | National Avg. |
| Fairview, OR | 9,382 | 38 | 24.0% |
| Wood Village, OR | 4,069 | 38 | 24.0% |
| Washougal, WA | 15,927 | 38 | 24.0% |
| Jennings Lodge, OR | 8,500 | 38 | 24.0% |
| Milwaukie, OR | 21,086 | 38 | 24.0% |
| Portland, OR | 650,380 | 38 | 24.0% |
| City | Population | Air Quality Index | National Avg. |
| Memphis, TN | 650,910 | 45 | 10.0% |
| Oklahoma City, OK | 649,821 | 48 | 4.0% |
| Las Vegas, NV | 644,594 | 54 | 8.0% |
| Nashville, TN | 667,070 | 45 | 10.0% |
| Detroit, MI | 672,351 | 56 | 12.0% |
| Portland, OR | 650,380 | 38 | 24.0% |
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