Union, Oregon has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 35.4 °F (low) to 61.1 °F (high). Annual precipitation averages 14.8 Inches. Union is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Sep.1 - Sep. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 24.4 °F | 38.3 °F | 1.21 in. |
| February | 26.2 °F | 43.7 °F | 0.98 in. |
| March | 29.7 °F | 52.0 °F | 1.24 in. |
| April | 33.4 °F | 58.6 °F | 1.78 in. |
| May | 39.9 °F | 67.7 °F | 2.53 in. |
| June | 45.1 °F | 74.6 °F | 1.56 in. |
| July | 49.8 °F | 86.1 °F | 0.45 in. |
| August | 48.3 °F | 86.6 °F | 0.5 in. |
| September | 41.3 °F | 77.5 °F | 0.61 in. |
| October | 33.7 °F | 62.8 °F | 1.16 in. |
| November | 29.0 °F | 47.5 °F | 1.55 in. |
| December | 23.8 °F | 38.3 °F | 1.26 in. |
| Annual | 35.4 °F | 61.1 °F | 14.83 in. |
| Average First Frost Date | Sep.1 - Sep. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | Over 180 Days |
| Plant Hardiness Zone | Zone 6b : -5°F to 0°F |
| Plant Hardiness Zone - 2012 | Zone 6b : -5°F to 0°F |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |