East Haddam, Connecticut has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 4.8 °C (low) to 15.5 °C (high). Annual precipitation averages 1309.1 Millimeters. East Haddam 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 | -6.8 °C | 2.2 °C | 100.58 mm |
| February | -6.2 °C | 3.6 °C | 86.36 mm |
| March | -2.3 °C | 7.8 °C | 119.38 mm |
| April | 3.2 °C | 14.7 °C | 116.08 mm |
| May | 8.3 °C | 20.3 °C | 95.25 mm |
| June | 13.7 °C | 25 °C | 114.3 mm |
| July | 16.7 °C | 27.9 °C | 97.54 mm |
| August | 16.1 °C | 27.2 °C | 110.49 mm |
| September | 11.9 °C | 23.4 °C | 114.81 mm |
| October | 6 °C | 17.1 °C | 128.52 mm |
| November | 0.8 °C | 10.9 °C | 105.66 mm |
| December | -3.4 °C | 5.4 °C | 120.14 mm |
| Annual | 4.8 °C | 15.5 °C | 1309.11 mm |
| 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 : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |