| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 36°F | 46°F | 41°F | 2.2" |
| February | 36°F | 49°F | 42°F | 1.4" |
| March | 38°F | 53°F | 45°F | 1.3" |
| April | 40°F | 57°F | 48°F | 0.9" |
| May | 43°F | 64°F | 52°F | 0.9" |
| June | 47°F | 68°F | 57°F | 0.4" |
| July | 49°F | 74°F | 60°F | 0.2" |
| August | 49°F | 74°F | 60°F | 0.4" |
| September | 48°F | 69°F | 57°F | 1.0" |
| October | 44°F | 59°F | 51°F | 1.7" |
| November | 39°F | 51°F | 45°F | 2.4" |
| December | 35°F | 45°F | 40°F | 2.0" |
| Index | Friday Harbor | 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. |
| Friday Harbor, WA | 2,463 | 34 | 32.0% |
| City | Population | Air Quality Index | National Avg. |
| Hudson, IA | 2,463 | 39 | 22.0% |
| Assiniboia, SK | 2,463 | n/a | |
| Beaverlodge, AB | 2,463 | n/a | |
| Parkwood, CA | 2,462 | 50 | = 100 |
| Rouses Point, NY | 2,462 | 37 | 26.0% |
| Friday Harbor, WA | 2,463 | 34 | 32.0% |