Harper, Oregon has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from 3 °C (low) to 18.1 °C (high). Annual precipitation averages 246.6 Millimeters. 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 | -6 °C | 3.1 °C | 34.04 mm |
| February | -3.8 °C | 7.4 °C | 20.07 mm |
| March | -0.7 °C | 13.5 °C | 18.8 mm |
| April | 1.9 °C | 17.7 °C | 18.03 mm |
| May | 6.6 °C | 22.8 °C | 30.73 mm |
| June | 10.4 °C | 27.5 °C | 21.84 mm |
| July | 14.1 °C | 33.5 °C | 10.92 mm |
| August | 12.8 °C | 32.8 °C | 8.13 mm |
| September | 7.8 °C | 27.1 °C | 8.89 mm |
| October | 1.8 °C | 18.9 °C | 17.02 mm |
| November | -2.9 °C | 9.6 °C | 20.07 mm |
| December | -5.8 °C | 3.4 °C | 38.1 mm |
| Annual | 3 °C | 18.1 °C | 246.64 mm |
| 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 : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |