Thomaston, Maine has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 2.6 °C (low) to 12.3 °C (high). Annual precipitation averages 1305.3 Millimeters. 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 | -10.2 °C | -0.7 °C | 114.3 mm |
| February | -9.4 °C | 0.6 °C | 96.01 mm |
| March | -4.8 °C | 4.6 °C | 121.16 mm |
| April | 0.9 °C | 10.8 °C | 119.63 mm |
| May | 6.3 °C | 16.5 °C | 95.5 mm |
| June | 11.3 °C | 21.3 °C | 102.62 mm |
| July | 14.7 °C | 24.7 °C | 82.8 mm |
| August | 14.2 °C | 24.4 °C | 76.2 mm |
| September | 10.4 °C | 20.7 °C | 112.78 mm |
| October | 4.6 °C | 14.2 °C | 133.86 mm |
| November | -0.6 °C | 8.3 °C | 124.21 mm |
| December | -6.2 °C | 2.6 °C | 126.24 mm |
| Annual | 2.6 °C | 12.3 °C | 1305.31 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 |