South Portland, Maine has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 4.4 °C (low) to 13.1 °C (high). Annual precipitation averages 1200.9 Millimeters. 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 | -8.6 °C | 0.1 °C | 89.15 mm |
| February | -7.6 °C | 1.4 °C | 89.15 mm |
| March | -3.1 °C | 5.1 °C | 102.62 mm |
| April | 2.6 °C | 11.3 °C | 108.2 mm |
| May | 8.1 °C | 17.1 °C | 91.95 mm |
| June | 13.4 °C | 22.4 °C | 107.95 mm |
| July | 16.4 °C | 25.4 °C | 86.11 mm |
| August | 16.4 °C | 25.3 °C | 84.33 mm |
| September | 12.2 °C | 21.4 °C | 103.12 mm |
| October | 6.2 °C | 15 °C | 117.35 mm |
| November | 0.8 °C | 8.9 °C | 106.17 mm |
| December | -4.6 °C | 3.5 °C | 114.81 mm |
| Annual | 4.4 °C | 13.1 °C | 1200.91 mm |
| 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 : -23.3°C to -20.6°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |