| 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 | Sultan | 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. |
| Lake Cassidy, WA | 2,854 | 24 | 52.0% |
| Lochsloy, WA | 2,991 | 24 | 52.0% |
| Lake Bosworth, WA | 1,071 | 24 | 52.0% |
| Cottage Lake, WA | 23,239 | 45 | 10.0% |
| Lake Stevens, WA | 33,470 | 45 | 10.0% |
| Sultan, WA | 5,330 | 45 | 10.0% |
| City | Population | Air Quality Index | National Avg. |
| Kahnawake, QC | 5,328 | n/a | |
| Uhrichsville, OH | 5,332 | 46 | 8.0% |
| Kalaheo, HI | 5,333 | 13 | 74.0% |
| Hightstown, NJ | 5,334 | 41 | 18.0% |
| Strawberry, CA | 5,325 | 40 | 20.0% |
| Sultan, WA | 5,330 | 45 | 10.0% |
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