Sumpter, Oregon has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from 29.6 °F (low) to 56.7 °F (high). Annual precipitation averages 19.4 Inches. Sumpter is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around Jun. 1 - Jun. 10 through the first frost around Sep.11 - Sep. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 16.0 °F | 35.0 °F | 2.63 in. |
| February | 18.1 °F | 40.0 °F | 1.75 in. |
| March | 23.1 °F | 47.0 °F | 1.92 in. |
| April | 27.8 °F | 53.3 °F | 1.61 in. |
| May | 34.3 °F | 62.4 °F | 2.02 in. |
| June | 39.4 °F | 70.2 °F | 1.42 in. |
| July | 44.9 °F | 82.1 °F | 0.58 in. |
| August | 44.1 °F | 82.3 °F | 0.59 in. |
| September | 37.4 °F | 73.1 °F | 0.63 in. |
| October | 29.9 °F | 58.4 °F | 1.22 in. |
| November | 23.3 °F | 43.2 °F | 2.14 in. |
| December | 16.3 °F | 33.9 °F | 2.91 in. |
| Annual | 29.6 °F | 56.7 °F | 19.42 in. |
| Average First Frost Date | Sep.11 - Sep. 20 |
| Average Last Frost Date | Jun. 1 - Jun. 10 |
| Average Days With Frost | Over 180 Days |
| Plant Hardiness Zone | Zone 6a : -10°F to -5°F |
| Plant Hardiness Zone - 2012 | Zone 5a : -20°F to -15°F |
| Current Drought Conditions | Extreme Drought |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |