| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 33°F | 47°F | 39°F | 4.8" |
| February | 34°F | 52°F | 42°F | 3.8" |
| March | 37°F | 56°F | 46°F | 4.5" |
| April | 39°F | 62°F | 50°F | 2.5" |
| May | 44°F | 70°F | 56°F | 2.1" |
| June | 49°F | 75°F | 61°F | 1.3" |
| July | 52°F | 84°F | 67°F | 0.3" |
| August | 52°F | 85°F | 68°F | 0.4" |
| September | 48°F | 78°F | 62°F | 1.4" |
| October | 42°F | 65°F | 52°F | 3.6" |
| November | 37°F | 53°F | 45°F | 5.8" |
| December | 32°F | 45°F | 38°F | 6.0" |
| Index | Bethany | Oregon | National |
| Air quality index | 38 | 32 | 42 |
| Pollution index | 15,149,900 | 7,156,356 | 2,726,193 |
| 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 | 0.010% |
| Benzene | 0.160% |
| Carbon Tetrachloride | 0.030% |
| Lead | 0.080% |
| Mercury | 0.010% |
| City | Population | Air Quality Index | National Avg. |
| Banks, OR | 1,897 | 38 | 24.0% |
| Brush Prairie, WA | 2,721 | 38 | 24.0% |
| Bull Mountain, OR | 9,732 | 38 | 24.0% |
| Gladstone, OR | 12,316 | 38 | 24.0% |
| Lake Oswego, OR | 39,476 | 38 | 24.0% |
| Bethany, OR | 28,047 | 38 | 24.0% |
| City | Population | Air Quality Index | National Avg. |
| East Chicago, IN | 28,044 | 55 | 10.0% |
| Melrose, MA | 28,054 | 43 | 14.0% |
| Saratoga Springs, NY | 28,056 | 37 | 26.0% |
| Zionsville, IN | 28,035 | 54 | 8.0% |
| Immokalee, FL | 28,060 | 34 | 32.0% |
| Bethany, OR | 28,047 | 38 | 24.0% |
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