| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 18°F | 30°F | 24°F | 1.2" |
| February | 25°F | 44°F | 33°F | 2.4" |
| March | 31°F | 57°F | 43°F | 1.8" |
| April | 35°F | 65°F | 50°F | 1.5" |
| May | 42°F | 75°F | 59°F | 2.6" |
| June | 49°F | 80°F | 64°F | 4.2" |
| July | 58°F | 92°F | 75°F | 1.6" |
| August | 54°F | 91°F | 73°F | 0.8" |
| September | 45°F | 78°F | 61°F | 2.2" |
| October | 37°F | 61°F | 48°F | 2.3" |
| November | 27°F | 41°F | 34°F | 3.6" |
| December | 18°F | 30°F | 25°F | 4.0" |
| Index | Winthrop | Washington | National |
| Air quality index | 24 | 36 | 42 |
| Pollution index | 422,626 | 4,541,850 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 298 |
| Days with moderate air quality | 66 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| 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. |
| Twisp, WA | 1,235 | 24 | 52.0% |
| Winthrop, WA | 340 | 24 | 52.0% |
| City | Population | Air Quality Index | National Avg. |
| St. Michael, AK | 340 | 31 | 38.0% |
| Cazadero, CA | 340 | 34 | 32.0% |
| Chilcoot-Vinton, CA | 340 | 46 | 8.0% |
| St. Marks, FL | 340 | 40 | 20.0% |
| Ryan, IA | 340 | 39 | 22.0% |
| Winthrop, WA | 340 | 24 | 52.0% |
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