| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 33°F | 46°F | 39°F | 10.0" |
| February | 33°F | 50°F | 41°F | 6.7" |
| March | 36°F | 54°F | 44°F | 9.7" |
| April | 37°F | 60°F | 47°F | 4.7" |
| May | 43°F | 67°F | 54°F | 3.1" |
| June | 48°F | 72°F | 58°F | 1.6" |
| July | 51°F | 79°F | 63°F | 0.8" |
| August | 51°F | 80°F | 64°F | 1.1" |
| September | 47°F | 74°F | 59°F | 3.0" |
| October | 42°F | 61°F | 50°F | 7.4" |
| November | 36°F | 51°F | 43°F | 13.6" |
| December | 32°F | 45°F | 38°F | 11.5" |
| Index | Union | Washington | National |
| Air quality index | 21 | 36 | 42 |
| Pollution index | 2,873,390 | 4,541,850 | 2,726,193 |
| Measurement | Total |
| Days measured | 361 |
| Days with good air quality | 339 |
| Days with moderate air quality | 22 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.050% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.010% |
| Mercury | 0.010% |
| City | Population | Air Quality Index | National Avg. |
| Grapeview, WA | 727 | 18 | 64.0% |
| Allyn, WA | 2,583 | 18 | 64.0% |
| Belfair, WA | 4,659 | 18 | 64.0% |
| Vaughn, WA | 1,093 | 18 | 64.0% |
| Hoodsport, WA | 143 | 21 | 58.0% |
| Union, WA | 334 | 21 | 58.0% |
| City | Population | Air Quality Index | National Avg. |
| Colt, AR | 334 | 45 | 10.0% |
| Oak Shores, CA | 334 | 46 | 8.0% |
| Bronson, IA | 334 | 35 | 30.0% |
| Arimo, ID | 334 | 27 | 46.0% |
| Hanaford, IL | 334 | 43 | 14.0% |
| Union, WA | 334 | 21 | 58.0% |