Winter Harbor, Maine has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 3.6 °C (low) to 11.8 °C (high). Annual precipitation averages 1343.1 Millimeters. Winter Harbor is located in USDA Plant Hardiness Zone 6a. 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 | -7.8 °C | -0.2 °C | 116.33 mm |
| February | -7.3 °C | 0.5 °C | 97.03 mm |
| March | -3.8 °C | 3.9 °C | 119.63 mm |
| April | 1.5 °C | 9.6 °C | 112.78 mm |
| May | 6.2 °C | 15.3 °C | 110.24 mm |
| June | 10.7 °C | 20.4 °C | 104.9 mm |
| July | 13.8 °C | 23.6 °C | 81.53 mm |
| August | 14.1 °C | 23.4 °C | 75.18 mm |
| September | 11.3 °C | 19.6 °C | 103.12 mm |
| October | 6.4 °C | 13.7 °C | 143.26 mm |
| November | 1.6 °C | 8.2 °C | 138.68 mm |
| December | -4 °C | 3.2 °C | 140.46 mm |
| Annual | 3.6 °C | 11.8 °C | 1343.14 mm |
| 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 6a : -23.3°C to -20.6°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |