Colchester, Connecticut has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 40 °F (low) to 60 °F (high). Annual precipitation averages 50.9 Inches. Colchester 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. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 18.8 °F | 36.3 °F | 3.92 in. |
| February | 19.9 °F | 38.8 °F | 3.36 in. |
| March | 27.3 °F | 46.5 °F | 4.64 in. |
| April | 37.0 °F | 58.7 °F | 4.52 in. |
| May | 46.7 °F | 68.8 °F | 3.7 in. |
| June | 56.2 °F | 77.2 °F | 4.27 in. |
| July | 61.9 °F | 82.4 °F | 3.87 in. |
| August | 60.4 °F | 81.1 °F | 4.33 in. |
| September | 52.7 °F | 74.3 °F | 4.58 in. |
| October | 41.7 °F | 62.8 °F | 4.95 in. |
| November | 32.2 °F | 51.7 °F | 4.1 in. |
| December | 24.8 °F | 41.9 °F | 4.7 in. |
| Annual | 40 °F | 60 °F | 50.94 in. |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 6b : -5°F to 0°F |
| Plant Hardiness Zone - 2012 | Zone 6a : -10°F to -5°F |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |