Sumner, Maine has a Subarctic With Cool Summers And Year Around Rainfall climate (Köppen classification: Dfc). Average annual temperatures range from 1.1 °C (low) to 12.2 °C (high). Annual precipitation averages 1230.9 Millimeters. Sumner is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around May 11 - May 20 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -12.9 °C | -2.6 °C | 85.09 mm |
| February | -12.3 °C | -0.9 °C | 75.95 mm |
| March | -6.8 °C | 3.9 °C | 89.92 mm |
| April | -0.2 °C | 11.1 °C | 106.43 mm |
| May | 5.9 °C | 18.3 °C | 97.79 mm |
| June | 11.2 °C | 22.9 °C | 128.27 mm |
| July | 14.2 °C | 25.9 °C | 101.35 mm |
| August | 13.2 °C | 25.4 °C | 103.89 mm |
| September | 8.8 °C | 21.3 °C | 89.15 mm |
| October | 2.9 °C | 13.9 °C | 139.7 mm |
| November | -2.5 °C | 6.9 °C | 105.92 mm |
| December | -8.2 °C | 0.7 °C | 107.44 mm |
| Annual | 1.1 °C | 12.2 °C | 1230.9 mm |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 11 - May 20 |
| Average Days With Frost | 150-180 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 | Normal |
| Köppen Climate Classification | Dfc - Subarctic With Cool Summers And Year Around Rainfall |