| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 35°F | 47°F | 40°F | 8.3" |
| February | 36°F | 52°F | 42°F | 5.4" |
| March | 40°F | 56°F | 46°F | 6.0" |
| April | 41°F | 62°F | 50°F | 4.8" |
| May | 47°F | 69°F | 56°F | 5.7" |
| June | 52°F | 73°F | 60°F | 3.6" |
| July | 55°F | 80°F | 65°F | 2.1" |
| August | 55°F | 81°F | 66°F | 2.8" |
| September | 51°F | 75°F | 61°F | 5.1" |
| October | 46°F | 63°F | 53°F | 6.4" |
| November | 40°F | 52°F | 45°F | 8.2" |
| December | 35°F | 45°F | 39°F | 8.9" |
| Index | Longview | Washington | National |
| Air quality index | 18 | 36 | 42 |
| Pollution index | 4,215,410 | 4,541,850 | 2,726,193 |
| Measurement | Total |
| Days measured | 360 |
| Days with good air quality | 338 |
| Days with moderate air quality | 22 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.005% |
| Benzene | 0.050% |
| Carbon Tetrachloride | 0.004% |
| Lead | 0.030% |
| Mercury | 0.250% |
| City | Population | Air Quality Index | National Avg. |
| Clatskanie, OR | 2,076 | 18 | 64.0% |
| Castle Rock, WA | 2,593 | 18 | 64.0% |
| West Side Highway, WA | 5,735 | 18 | 64.0% |
| Deer Island, OR | 375 | 18 | 64.0% |
| Kalama, WA | 2,596 | 18 | 64.0% |
| Longview, WA | 36,720 | 18 | 64.0% |
| City | Population | Air Quality Index | National Avg. |
| Hot Springs, AR | 36,711 | 38 | 24.0% |
| Campbell River, BC | 36,740 | n/a | |
| Oakton, VA | 36,748 | 47 | 6.0% |
| Milton, GA | 36,755 | 52 | 4.0% |
| Pleasant Grove, UT | 36,678 | 46 | 8.0% |
| Longview, WA | 36,720 | 18 | 64.0% |
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