Thomaston, Connecticut has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 3.9 °C (low) to 16 °C (high). Annual precipitation averages 1323.8 Millimeters. Thomaston is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -8.2 °C | 2.2 °C | 89.66 mm |
| February | -7.6 °C | 3.9 °C | 80.26 mm |
| March | -3.4 °C | 8.3 °C | 111 mm |
| April | 2.2 °C | 15.4 °C | 100.58 mm |
| May | 7.9 °C | 21.6 °C | 104.9 mm |
| June | 13.2 °C | 26.3 °C | 116.59 mm |
| July | 16.2 °C | 29.1 °C | 121.92 mm |
| August | 15.3 °C | 27.9 °C | 120.9 mm |
| September | 11.2 °C | 24 °C | 117.6 mm |
| October | 4.8 °C | 17.2 °C | 140.72 mm |
| November | -0.6 °C | 10.8 °C | 102.62 mm |
| December | -4.8 °C | 4.9 °C | 117.09 mm |
| Annual | 3.9 °C | 16 °C | 1323.84 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |