| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 34°F | 48°F | 40°F | 5.4" |
| February | 36°F | 52°F | 43°F | 3.7" |
| March | 39°F | 57°F | 47°F | 4.9" |
| April | 42°F | 63°F | 52°F | 2.9" |
| May | 48°F | 71°F | 58°F | 2.6" |
| June | 53°F | 76°F | 63°F | 1.7" |
| July | 57°F | 84°F | 69°F | 0.5" |
| August | 57°F | 84°F | 69°F | 0.4" |
| September | 52°F | 79°F | 64°F | 1.5" |
| October | 46°F | 66°F | 55°F | 3.7" |
| November | 40°F | 54°F | 47°F | 6.2" |
| December | 34°F | 47°F | 40°F | 6.2" |
| Index | Yacolt | Washington | National |
| Air quality index | 38 | 36 | 42 |
| Pollution index | 1,899,410 | 4,541,850 | 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 | 0.003% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.010% |
| Mercury | 0.002% |
| City | Population | Air Quality Index | National Avg. |
| Hockinson, WA | 6,159 | 38 | 24.0% |
| Venersborg, WA | 3,973 | 38 | 24.0% |
| Barberton, WA | 7,317 | 38 | 24.0% |
| Lake Shore, WA | 7,581 | 38 | 24.0% |
| Walnut Grove, WA | 9,324 | 38 | 24.0% |
| Yacolt, WA | 1,686 | 38 | 24.0% |
| City | Population | Air Quality Index | National Avg. |
| Bernice, LA | 1,686 | 35 | 30.0% |
| Hallsville, MO | 1,686 | 38 | 24.0% |
| Voorhees, NJ | 1,686 | 51 | 2.0% |
| Depoe Bay, OR | 1,686 | 17 | 66.0% |
| Grant, AL | 1,685 | 44 | 12.0% |
| Yacolt, WA | 1,686 | 38 | 24.0% |
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