| 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 | Lewisville | 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. |
| Columbia City, OR | 1,770 | 18 | 64.0% |
| St. Helens, OR | 13,779 | 18 | 64.0% |
| Woodland, WA | 6,223 | 18 | 64.0% |
| Brush Prairie, WA | 2,721 | 38 | 24.0% |
| Meadow Glade, WA | 2,774 | 38 | 24.0% |
| Lewisville, WA | 2,166 | 38 | 24.0% |
| City | Population | Air Quality Index | National Avg. |
| Rockwell City, IA | 2,166 | 37 | 26.0% |
| Oakwood, PA | 2,166 | 31 | 38.0% |
| Fort Qu'Appelle, SK | 2,166 | n/a | |
| Carnation, WA | 2,165 | 45 | 10.0% |
| Saint-Gédéon-de-Beauce, QC | 2,165 | n/a | |
| Lewisville, WA | 2,166 | 38 | 24.0% |
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