Belfast, Maine has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 35.4 °F (low) to 54.6 °F (high). Annual precipitation averages 48.8 Inches. Belfast is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 11.3 °F | 29.7 °F | 3.98 in. |
| February | 12.8 °F | 32.5 °F | 3.25 in. |
| March | 21.5 °F | 40.0 °F | 3.87 in. |
| April | 32.5 °F | 52.0 °F | 4.42 in. |
| May | 42.6 °F | 63.3 °F | 3.82 in. |
| June | 52.1 °F | 72.1 °F | 4.33 in. |
| July | 58.0 °F | 77.9 °F | 3.14 in. |
| August | 57.0 °F | 77.4 °F | 3.25 in. |
| September | 49.5 °F | 70.2 °F | 3.95 in. |
| October | 39.2 °F | 58.0 °F | 5.49 in. |
| November | 29.8 °F | 46.3 °F | 4.66 in. |
| December | 19.0 °F | 35.6 °F | 4.59 in. |
| Annual | 35.4 °F | 54.6 °F | 48.75 in. |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 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 | Moderate Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |