Haddam, Connecticut has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 41 °F (low) to 60.3 °F (high). Annual precipitation averages 52.8 Inches. Haddam is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 20.2 °F | 36.7 °F | 4.06 in. |
| February | 21.3 °F | 39.3 °F | 3.47 in. |
| March | 28.1 °F | 46.9 °F | 4.75 in. |
| April | 38.0 °F | 58.7 °F | 4.59 in. |
| May | 47.3 °F | 68.9 °F | 3.81 in. |
| June | 56.8 °F | 77.6 °F | 4.94 in. |
| July | 62.3 °F | 82.8 °F | 3.91 in. |
| August | 61.1 °F | 81.3 °F | 4.46 in. |
| September | 53.8 °F | 74.3 °F | 4.45 in. |
| October | 43.0 °F | 62.8 °F | 5.33 in. |
| November | 33.6 °F | 52.0 °F | 4.28 in. |
| December | 26.2 °F | 42.3 °F | 4.77 in. |
| Annual | 41 °F | 60.3 °F | 52.82 in. |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 100-125 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 |