| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 36°F | 46°F | 41°F | 3.8" |
| February | 37°F | 49°F | 42°F | 2.7" |
| March | 39°F | 52°F | 45°F | 4.4" |
| April | 42°F | 57°F | 48°F | 2.8" |
| May | 47°F | 64°F | 54°F | 2.2" |
| June | 51°F | 68°F | 58°F | 1.8" |
| July | 55°F | 74°F | 63°F | 0.7" |
| August | 56°F | 75°F | 63°F | 0.9" |
| September | 53°F | 69°F | 59°F | 2.0" |
| October | 47°F | 59°F | 52°F | 3.6" |
| November | 40°F | 51°F | 45°F | 5.7" |
| December | 35°F | 44°F | 39°F | 4.9" |
| Index | Mukilteo | 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. |
| Keyport, WA | 339 | 18 | 64.0% |
| Freeland, WA | 1,883 | 24 | 52.0% |
| North Marysville, WA | 138 | 24 | 52.0% |
| Langley, WA | 1,201 | 24 | 52.0% |
| Lake Bosworth, WA | 1,071 | 24 | 52.0% |
| Mukilteo, WA | 21,414 | 45 | 10.0% |
| City | Population | Air Quality Index | National Avg. |
| Portsmouth, NH | 21,418 | 37 | 26.0% |
| North Bellmore, NY | 21,422 | 51 | 2.0% |
| Duarte, CA | 21,399 | 72 | 44.0% |
| Bear, DE | 21,397 | 42 | 16.0% |
| Ensley, FL | 21,397 | 41 | 18.0% |
| Mukilteo, WA | 21,414 | 45 | 10.0% |
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