Union, Oregon has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 1.9 °C (low) to 16.2 °C (high). Annual precipitation averages 376.7 Millimeters. 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 | -4.2 °C | 3.5 °C | 30.73 mm |
| February | -3.2 °C | 6.5 °C | 24.89 mm |
| March | -1.3 °C | 11.1 °C | 31.5 mm |
| April | 0.8 °C | 14.8 °C | 45.21 mm |
| May | 4.4 °C | 19.8 °C | 64.26 mm |
| June | 7.3 °C | 23.7 °C | 39.62 mm |
| July | 9.9 °C | 30.1 °C | 11.43 mm |
| August | 9.1 °C | 30.3 °C | 12.7 mm |
| September | 5.2 °C | 25.3 °C | 15.49 mm |
| October | 0.9 °C | 17.1 °C | 29.46 mm |
| November | -1.7 °C | 8.6 °C | 39.37 mm |
| December | -4.6 °C | 3.5 °C | 32 mm |
| Annual | 1.9 °C | 16.2 °C | 376.66 mm |
| 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 : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Extreme Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |