Jefferson, Maine has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 36.7 °F (low) to 55 °F (high). Annual precipitation averages 49.1 Inches. Jefferson is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 11.8 °F | 29.8 °F | 3.76 in. |
| February | 13.9 °F | 32.8 °F | 3.38 in. |
| March | 23.1 °F | 40.7 °F | 4.11 in. |
| April | 33.8 °F | 52.9 °F | 4.37 in. |
| May | 44.2 °F | 64.1 °F | 3.7 in. |
| June | 53.6 °F | 72.8 °F | 4.43 in. |
| July | 59.5 °F | 78.5 °F | 3.43 in. |
| August | 58.4 °F | 77.6 °F | 3.37 in. |
| September | 51.1 °F | 70.4 °F | 4.0 in. |
| October | 40.3 °F | 58.0 °F | 5.4 in. |
| November | 30.5 °F | 46.4 °F | 4.56 in. |
| December | 20.0 °F | 35.7 °F | 4.61 in. |
| Annual | 36.7 °F | 55 °F | 49.12 in. |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5b : -15°F to -10°F |
| Plant Hardiness Zone - 2012 | Zone 5a : -20°F to -15°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |