| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 36°F | 47°F | 41°F | 7.4" |
| February | 37°F | 50°F | 42°F | 3.8" |
| March | 40°F | 54°F | 46°F | 5.8" |
| April | 43°F | 58°F | 50°F | 2.8" |
| May | 48°F | 65°F | 56°F | 2.9" |
| June | 53°F | 68°F | 60°F | 1.8" |
| July | 56°F | 73°F | 64°F | 1.0" |
| August | 56°F | 73°F | 64°F | 1.4" |
| September | 52°F | 68°F | 59°F | 3.2" |
| October | 46°F | 60°F | 52°F | 5.3" |
| November | 40°F | 51°F | 45°F | 6.7" |
| December | 34°F | 45°F | 39°F | 6.3" |
| Index | Custer | Washington | National |
| Air quality index | 34 | 36 | 42 |
| Pollution index | 480,925 | 4,541,850 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 277 |
| Days with moderate air quality | 78 |
| Days w/ poor A.Q. for sensitive groups | 10 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.000% |
| Benzene | 0.010% |
| Carbon Tetrachloride | 0.001% |
| Lead | 0.040% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Marietta-Alderwood, WA | 3,463 | 34 | 32.0% |
| Geneva, WA | 2,596 | 34 | 32.0% |
| Bellingham, WA | 90,821 | 34 | 32.0% |
| Birch Bay, WA | 9,917 | 34 | 32.0% |
| Nooksack, WA | 1,594 | 34 | 32.0% |
| Custer, WA | 298 | 34 | 32.0% |
| City | Population | Air Quality Index | National Avg. |
| Akiak, AK | 298 | 31 | 38.0% |
| Goose Lake, IA | 298 | 42 | 16.0% |
| Weippe, ID | 298 | 29 | 42.0% |
| Taylor, MS | 298 | 33 | 34.0% |
| Toccopola, MS | 298 | 39 | 22.0% |
| Custer, WA | 298 | 34 | 32.0% |
Here are the best places to live in Washington
Most Dangerous Cities In The US
These are the 10 cheapest cities in Washington
See the best places to live in Custer