Jefferson, Maine has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 2.6 °C (low) to 12.8 °C (high). Annual precipitation averages 1247.6 Millimeters. 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 | -11.2 °C | -1.2 °C | 95.5 mm |
| February | -10.1 °C | 0.4 °C | 85.85 mm |
| March | -4.9 °C | 4.8 °C | 104.39 mm |
| April | 1 °C | 11.6 °C | 111 mm |
| May | 6.8 °C | 17.8 °C | 93.98 mm |
| June | 12 °C | 22.7 °C | 112.52 mm |
| July | 15.3 °C | 25.8 °C | 87.12 mm |
| August | 14.7 °C | 25.3 °C | 85.6 mm |
| September | 10.6 °C | 21.3 °C | 101.6 mm |
| October | 4.6 °C | 14.4 °C | 137.16 mm |
| November | -0.8 °C | 8 °C | 115.82 mm |
| December | -6.7 °C | 2.1 °C | 117.09 mm |
| Annual | 2.6 °C | 12.8 °C | 1247.63 mm |
| 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 : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |