| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 26°F | 39°F | 32°F | 2.0" |
| February | 30°F | 46°F | 37°F | 2.1" |
| March | 33°F | 54°F | 42°F | 2.0" |
| April | 36°F | 61°F | 47°F | 2.2" |
| May | 42°F | 69°F | 55°F | 4.0" |
| June | 48°F | 77°F | 62°F | 3.8" |
| July | 53°F | 89°F | 71°F | 2.6" |
| August | 50°F | 88°F | 69°F | 2.2" |
| September | 43°F | 79°F | 60°F | 2.0" |
| October | 37°F | 64°F | 49°F | 2.4" |
| November | 32°F | 49°F | 40°F | 1.9" |
| December | 25°F | 38°F | 31°F | 2.2" |
| Index | Union | Oregon | National |
| Air quality index | 20 | 32 | 42 |
| Pollution index | 1,082,340 | 7,156,356 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 344 |
| Days with moderate air quality | 21 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.000% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.001% |
| Lead | 0.002% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Cove, OR | 735 | 20 | 60.0% |
| Island City, OR | 1,108 | 20 | 60.0% |
| La Grande, OR | 13,380 | 20 | 60.0% |
| North Powder, OR | 616 | 20 | 60.0% |
| Union, OR | 1,841 | 20 | 60.0% |
| City | Population | Air Quality Index | National Avg. |
| Waterville, MN | 1,841 | 46 | 8.0% |
| Cleary, MS | 1,841 | 44 | 12.0% |
| Shannon, MS | 1,841 | 39 | 22.0% |
| Arkoma, OK | 1,841 | 36 | 28.0% |
| Walden, TN | 1,841 | 46 | 8.0% |
| Union, OR | 1,841 | 20 | 60.0% |
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