Jefferson, Oregon has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 43 °F (low) to 63.6 °F (high). Annual precipitation averages 43.7 Inches. 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 | 35.2 °F | 47.5 °F | 6.08 in. |
| February | 35.3 °F | 51.4 °F | 4.75 in. |
| March | 37.5 °F | 56.2 °F | 5.03 in. |
| April | 40.5 °F | 61.3 °F | 3.74 in. |
| May | 45.6 °F | 68.0 °F | 2.61 in. |
| June | 49.6 °F | 73.4 °F | 1.65 in. |
| July | 53.3 °F | 82.1 °F | 0.37 in. |
| August | 52.9 °F | 82.6 °F | 0.45 in. |
| September | 49.1 °F | 76.9 °F | 1.59 in. |
| October | 43.1 °F | 64.6 °F | 3.76 in. |
| November | 38.5 °F | 53.1 °F | 6.29 in. |
| December | 34.8 °F | 46.6 °F | 7.33 in. |
| Annual | 43 °F | 63.6 °F | 43.65 in. |
| 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 : 15°F to 20°F |
| Plant Hardiness Zone - 2012 | Zone 8b : 15°F to 20°F |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |