| 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 | Kelso | 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. |
| Deer Island, OR | 105 | 18 | 64.0% |
| Kalama, WA | 2,708 | 18 | 64.0% |
| Prescott, OR | 85 | 18 | 64.0% |
| Longview, WA | 37,914 | 18 | 64.0% |
| Rainier, OR | 2,080 | 18 | 64.0% |
| Kelso, WA | 12,237 | 18 | 64.0% |
| City | Population | Air Quality Index | National Avg. |
| Palmer Town, MA | 12,236 | 40 | 20.0% |
| Northlake, IL | 12,235 | 55 | 10.0% |
| Orange City, FL | 12,232 | 37 | 26.0% |
| Carnot-Moon, PA | 12,242 | 56 | 12.0% |
| Mays Chapel, MD | 12,229 | 46 | 8.0% |
| Kelso, WA | 12,237 | 18 | 64.0% |
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