Sullivan, Maine has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 36.3 °F (low) to 54.2 °F (high). Annual precipitation averages 50.7 Inches. Sullivan 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. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 14.4 °F | 29.6 °F | 4.29 in. |
| February | 15.5 °F | 32.1 °F | 3.62 in. |
| March | 22.2 °F | 39.5 °F | 4.44 in. |
| April | 32.3 °F | 51.4 °F | 4.32 in. |
| May | 42.4 °F | 62.5 °F | 4.1 in. |
| June | 51.3 °F | 71.5 °F | 3.99 in. |
| July | 57.5 °F | 77.3 °F | 3.24 in. |
| August | 56.6 °F | 76.9 °F | 2.95 in. |
| September | 49.5 °F | 69.7 °F | 3.93 in. |
| October | 40.3 °F | 57.6 °F | 5.46 in. |
| November | 31.7 °F | 46.1 °F | 5.12 in. |
| December | 21.4 °F | 35.7 °F | 5.2 in. |
| Annual | 36.3 °F | 54.2 °F | 50.66 in. |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| 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 5b : -15°F to -10°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |