| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 35°F | 45°F | 40°F | 1.2" |
| February | 37°F | 48°F | 41°F | 2.3" |
| March | 40°F | 51°F | 45°F | 2.5" |
| April | 42°F | 56°F | 48°F | 0.6" |
| May | 46°F | 61°F | 53°F | 1.2" |
| June | 50°F | 66°F | 57°F | 0.9" |
| July | 52°F | 71°F | 60°F | 0.0" |
| August | 52°F | 71°F | 61°F | 0.0" |
| September | 50°F | 66°F | 57°F | 0.5" |
| October | 45°F | 57°F | 51°F | 2.9" |
| November | 40°F | 50°F | 44°F | 2.4" |
| December | 35°F | 44°F | 39°F | 1.4" |
| Index | Hamilton | Washington | National |
| Air quality index | 24 | 36 | 42 |
| Pollution index | 15,778,900 | 4,541,850 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 361 |
| Days with moderate air quality | 4 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.270% |
| Carbon Tetrachloride | 0.040% |
| Lead | 0.160% |
| Mercury | 0.003% |
| City | Population | Air Quality Index | National Avg. |
| Lake Cavanaugh, WA | 220 | 24 | 52.0% |
| Lake McMurray, WA | 478 | 24 | 52.0% |
| Concrete, WA | 915 | 24 | 52.0% |
| Lyman, WA | 277 | 24 | 52.0% |
| Sedro-Woolley, WA | 11,919 | 24 | 52.0% |
| Hamilton, WA | 311 | 24 | 52.0% |
| City | Population | Air Quality Index | National Avg. |
| Waucoma, IA | 311 | 39 | 22.0% |
| Plevna, MT | 311 | 33 | 34.0% |
| Macclesfield, NC | 311 | 36 | 28.0% |
| Bridgeville, NJ | 311 | 34 | 32.0% |
| Rosewood, OH | 311 | 45 | 10.0% |
| Hamilton, WA | 311 | 24 | 52.0% |
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