South Thomaston, Maine has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 3.4 °C (low) to 12 °C (high). Annual precipitation averages 1299.7 Millimeters. South Thomaston 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 | -8.4 °C | -0.1 °C | 113.79 mm |
| February | -7.9 °C | 0.8 °C | 95.5 mm |
| March | -4.1 °C | 4.3 °C | 120.9 mm |
| April | 1.5 °C | 10.2 °C | 118.87 mm |
| May | 6.5 °C | 15.6 °C | 95.5 mm |
| June | 11.2 °C | 20.4 °C | 101.85 mm |
| July | 14.6 °C | 23.8 °C | 82.55 mm |
| August | 14.3 °C | 23.7 °C | 75.95 mm |
| September | 10.9 °C | 20.1 °C | 112.27 mm |
| October | 5.7 °C | 13.9 °C | 133.1 mm |
| November | 0.9 °C | 8.6 °C | 123.44 mm |
| December | -4.6 °C | 3.2 °C | 125.98 mm |
| Annual | 3.4 °C | 12 °C | 1299.7 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 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |