Jefferson, Oregon has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 6.1 °C (low) to 17.6 °C (high). Annual precipitation averages 1108.7 Millimeters. Jefferson is located in USDA Plant Hardiness Zone 8b. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 1.8 °C | 8.6 °C | 154.43 mm |
| February | 1.8 °C | 10.8 °C | 120.65 mm |
| March | 3.1 °C | 13.4 °C | 127.76 mm |
| April | 4.7 °C | 16.3 °C | 95 mm |
| May | 7.6 °C | 20 °C | 66.29 mm |
| June | 9.8 °C | 23 °C | 41.91 mm |
| July | 11.8 °C | 27.8 °C | 9.4 mm |
| August | 11.6 °C | 28.1 °C | 11.43 mm |
| September | 9.5 °C | 24.9 °C | 40.39 mm |
| October | 6.2 °C | 18.1 °C | 95.5 mm |
| November | 3.6 °C | 11.7 °C | 159.77 mm |
| December | 1.6 °C | 8.1 °C | 186.18 mm |
| Annual | 6.1 °C | 17.6 °C | 1108.71 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 50-75 Days |
| Plant Hardiness Zone | Zone 8b : -9.4°C to -6.7°C |
| Plant Hardiness Zone - 2012 | Zone 8b : -9.4°C to -6.7°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |