Harper, Oregon has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from 37.4 °F (low) to 64.6 °F (high). Annual precipitation averages 9.7 Inches. Harper 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 Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 21.2 °F | 37.5 °F | 1.34 in. |
| February | 25.2 °F | 45.3 °F | 0.79 in. |
| March | 30.7 °F | 56.3 °F | 0.74 in. |
| April | 35.4 °F | 63.8 °F | 0.71 in. |
| May | 43.9 °F | 73.1 °F | 1.21 in. |
| June | 50.8 °F | 81.5 °F | 0.86 in. |
| July | 57.3 °F | 92.3 °F | 0.43 in. |
| August | 55.0 °F | 91.0 °F | 0.32 in. |
| September | 46.0 °F | 80.8 °F | 0.35 in. |
| October | 35.3 °F | 66.1 °F | 0.67 in. |
| November | 26.8 °F | 49.3 °F | 0.79 in. |
| December | 21.5 °F | 38.1 °F | 1.5 in. |
| Annual | 37.4 °F | 64.6 °F | 9.71 in. |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 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 | Moderate Drought |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |