| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 35°F | 45°F | 40°F | 2.5" |
| February | 36°F | 50°F | 42°F | 2.8" |
| March | 41°F | 55°F | 47°F | 3.5" |
| April | 43°F | 58°F | 49°F | 3.5" |
| May | 48°F | 65°F | 55°F | 3.0" |
| June | 51°F | 66°F | 57°F | 2.2" |
| July | 55°F | 74°F | 63°F | 2.0" |
| August | 55°F | 74°F | 62°F | 1.7" |
| September | 50°F | 66°F | 57°F | 2.8" |
| October | 46°F | 59°F | 51°F | 3.4" |
| November | 38°F | 48°F | 43°F | 4.8" |
| December | 35°F | 45°F | 39°F | 8.6" |
| Index | Duvall | Washington | National |
| Air quality index | 45 | 36 | 42 |
| Pollution index | 43,367,400 | 4,541,850 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 236 |
| Days with moderate air quality | 127 |
| Days w/ poor A.Q. for sensitive groups | 2 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.020% |
| Benzene | 0.790% |
| Carbon Tetrachloride | 0.120% |
| Lead | 0.210% |
| Mercury | 0.180% |
| City | Population | Air Quality Index | National Avg. |
| Cathcart, WA | 2,278 | 45 | 10.0% |
| Issaquah, WA | 38,707 | 45 | 10.0% |
| Gold Bar, WA | 1,995 | 45 | 10.0% |
| Lake Forest Park, WA | 13,455 | 45 | 10.0% |
| Eastmont, WA | 22,829 | 45 | 10.0% |
| Duvall, WA | 7,979 | 45 | 10.0% |
| City | Population | Air Quality Index | National Avg. |
| Mayo, MD | 7,979 | 47 | 6.0% |
| Wyoming, MN | 7,976 | 46 | 8.0% |
| Greenbriar, VA | 7,976 | 47 | 6.0% |
| Brentwood, MO | 7,986 | 54 | 8.0% |
| Beckwith, ON | 7,986 | n/a | |
| Duvall, WA | 7,979 | 45 | 10.0% |
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