| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 23°F | 33°F | 27°F | 12.2" |
| February | 26°F | 35°F | 30°F | 7.2" |
| March | 29°F | 39°F | 33°F | 11.1" |
| April | 32°F | 46°F | 37°F | 6.3" |
| May | 39°F | 55°F | 45°F | 5.8" |
| June | 43°F | 60°F | 49°F | 4.4" |
| July | 49°F | 70°F | 57°F | 1.2" |
| August | 51°F | 70°F | 58°F | 1.5" |
| September | 46°F | 63°F | 52°F | 4.1" |
| October | 38°F | 50°F | 42°F | 9.1" |
| November | 30°F | 37°F | 33°F | 14.5" |
| December | 23°F | 31°F | 26°F | 12.2" |
| Index | Roslyn | Washington | National |
| Air quality index | 23 | 36 | 42 |
| Pollution index | 422,626 | 4,541,850 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 305 |
| Days with moderate air quality | 60 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.000% |
| Benzene | 0.010% |
| Carbon Tetrachloride | 0.001% |
| Lead | 0.000% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| South Cle Elum, WA | 799 | 23 | 54.0% |
| Cle Elum, WA | 2,662 | 23 | 54.0% |
| Easton, WA | 302 | 23 | 54.0% |
| Ronald, WA | 202 | 23 | 54.0% |
| Roslyn, WA | 608 | 23 | 54.0% |
| City | Population | Air Quality Index | National Avg. |
| Tazlina, AK | 608 | 31 | 38.0% |
| Gasquet, CA | 608 | 20 | 60.0% |
| Westwood city, KY | 608 | 42 | 16.0% |
| Port Austin, MI | 608 | 26 | 48.0% |
| Butterfield, MO | 608 | 18 | 64.0% |
| Roslyn, WA | 608 | 23 | 54.0% |
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