South Portland, Maine has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 39.8 °F (low) to 55.6 °F (high). Annual precipitation averages 47.3 Inches. South Portland is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 16.5 °F | 32.2 °F | 3.51 in. |
| February | 18.3 °F | 34.6 °F | 3.51 in. |
| March | 26.4 °F | 41.2 °F | 4.04 in. |
| April | 36.7 °F | 52.4 °F | 4.26 in. |
| May | 46.5 °F | 62.7 °F | 3.62 in. |
| June | 56.1 °F | 72.4 °F | 4.25 in. |
| July | 61.6 °F | 77.7 °F | 3.39 in. |
| August | 61.5 °F | 77.6 °F | 3.32 in. |
| September | 54.0 °F | 70.6 °F | 4.06 in. |
| October | 43.1 °F | 59.0 °F | 4.62 in. |
| November | 33.4 °F | 48.1 °F | 4.18 in. |
| December | 23.8 °F | 38.3 °F | 4.52 in. |
| Annual | 39.8 °F | 55.6 °F | 47.28 in. |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 6a : -10°F to -5°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 |