Hermiston, Oregon has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from 5.3 °C (low) to 18.5 °C (high). Annual precipitation averages 225.3 Millimeters. Hermiston is located in USDA Plant Hardiness Zone 7b. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -1.9 °C | 5.5 °C | 30.73 mm |
| February | -1.5 °C | 8.8 °C | 22.86 mm |
| March | 1 °C | 14.1 °C | 20.83 mm |
| April | 4.1 °C | 18.3 °C | 19.05 mm |
| May | 8.2 °C | 23.3 °C | 22.61 mm |
| June | 11.6 °C | 27 °C | 14.73 mm |
| July | 14.8 °C | 32.3 °C | 3.56 mm |
| August | 14.3 °C | 31.8 °C | 5.33 mm |
| September | 9.8 °C | 26.7 °C | 7.87 mm |
| October | 4.5 °C | 18.6 °C | 20.57 mm |
| November | 0.4 °C | 10.3 °C | 26.42 mm |
| December | -1.9 °C | 5.2 °C | 30.73 mm |
| Annual | 5.3 °C | 18.5 °C | 225.29 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 75-100 Days |
| Plant Hardiness Zone | Zone 7b : -15°C to -12.2°C |
| Plant Hardiness Zone - 2012 | Zone 7a : -17.8°C to -15°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |