Sumner, Maine has a Subarctic With Cool Summers And Year Around Rainfall climate (Köppen classification: Dfc). Average annual temperatures range from 34 °F (low) to 54 °F (high). Annual precipitation averages 48.5 Inches. 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 | 8.8 °F | 27.3 °F | 3.35 in. |
| February | 9.9 °F | 30.3 °F | 2.99 in. |
| March | 19.8 °F | 39.0 °F | 3.54 in. |
| April | 31.6 °F | 52.0 °F | 4.19 in. |
| May | 42.7 °F | 64.9 °F | 3.85 in. |
| June | 52.2 °F | 73.3 °F | 5.05 in. |
| July | 57.6 °F | 78.7 °F | 3.99 in. |
| August | 55.8 °F | 77.7 °F | 4.09 in. |
| September | 47.8 °F | 70.3 °F | 3.51 in. |
| October | 37.2 °F | 57.1 °F | 5.5 in. |
| November | 27.5 °F | 44.5 °F | 4.17 in. |
| December | 17.2 °F | 33.3 °F | 4.23 in. |
| Annual | 34 °F | 54 °F | 48.46 in. |
| 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 : -15°F to -10°F |
| Plant Hardiness Zone - 2012 | Zone 5a : -20°F to -15°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfc - Subarctic With Cool Summers And Year Around Rainfall |