Sumpter, Oregon has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from -1.4 °C (low) to 13.7 °C (high). Annual precipitation averages 493.3 Millimeters. 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 | -8.9 °C | 1.7 °C | 66.8 mm |
| February | -7.7 °C | 4.4 °C | 44.45 mm |
| March | -4.9 °C | 8.3 °C | 48.77 mm |
| April | -2.3 °C | 11.8 °C | 40.89 mm |
| May | 1.3 °C | 16.9 °C | 51.31 mm |
| June | 4.1 °C | 21.2 °C | 36.07 mm |
| July | 7.2 °C | 27.8 °C | 14.73 mm |
| August | 6.7 °C | 27.9 °C | 14.99 mm |
| September | 3 °C | 22.8 °C | 16 mm |
| October | -1.2 °C | 14.7 °C | 30.99 mm |
| November | -4.8 °C | 6.2 °C | 54.36 mm |
| December | -8.7 °C | 1.1 °C | 73.91 mm |
| Annual | -1.4 °C | 13.7 °C | 493.27 mm |
| 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 : -23.3°C to -20.6°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Extreme Drought |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |