| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 36°F | 46°F | 41°F | 6.0" |
| February | 38°F | 49°F | 43°F | 4.2" |
| March | 39°F | 53°F | 45°F | 5.8" |
| April | 42°F | 58°F | 49°F | 3.1" |
| May | 47°F | 66°F | 55°F | 2.4" |
| June | 51°F | 71°F | 59°F | 1.3" |
| July | 55°F | 77°F | 64°F | 0.6" |
| August | 55°F | 77°F | 65°F | 0.8" |
| September | 52°F | 71°F | 60°F | 1.5" |
| October | 47°F | 60°F | 52°F | 4.5" |
| November | 41°F | 51°F | 46°F | 6.8" |
| December | 36°F | 45°F | 40°F | 5.8" |
| Index | Longbranch | Washington | National |
| Air quality index | 30 | 36 | 42 |
| Pollution index | 6,704,330 | 4,541,850 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 323 |
| Days with moderate air quality | 42 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.003% |
| Benzene | 0.100% |
| Carbon Tetrachloride | 0.004% |
| Lead | 0.030% |
| Mercury | 0.003% |
| City | Population | Air Quality Index | National Avg. |
| Grapeview, WA | 703 | 18 | 64.0% |
| Wauna, WA | 4,509 | 18 | 64.0% |
| Purdy, WA | 1,531 | 18 | 64.0% |
| Maplewood, WA | 5,135 | 18 | 64.0% |
| Stansberry Lake, WA | 2,389 | 18 | 64.0% |
| Longbranch, WA | 4,568 | 30 | 40.0% |
| City | Population | Air Quality Index | National Avg. |
| Portola Valley, CA | 4,568 | 43 | 14.0% |
| Humboldt, IA | 4,568 | 37 | 26.0% |
| Rio Communities, NM | 4,566 | 53 | 6.0% |
| Williamstown, MA | 4,565 | 35 | 30.0% |
| Hollister, MO | 4,564 | 18 | 64.0% |
| Longbranch, WA | 4,568 | 30 | 40.0% |
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