Marlborough, Connecticut has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 40.3 °F (low) to 60.2 °F (high). Annual precipitation averages 50.3 Inches. Marlborough 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 | 18.7 °F | 36.3 °F | 3.75 in. |
| February | 20.0 °F | 38.9 °F | 3.25 in. |
| March | 27.5 °F | 46.7 °F | 4.49 in. |
| April | 37.5 °F | 58.9 °F | 4.32 in. |
| May | 47.3 °F | 69.2 °F | 3.72 in. |
| June | 56.7 °F | 77.6 °F | 4.41 in. |
| July | 62.3 °F | 82.8 °F | 4.02 in. |
| August | 60.8 °F | 81.4 °F | 4.29 in. |
| September | 53.2 °F | 74.5 °F | 4.5 in. |
| October | 41.9 °F | 62.9 °F | 4.97 in. |
| November | 32.4 °F | 51.8 °F | 3.97 in. |
| December | 24.7 °F | 41.9 °F | 4.56 in. |
| Annual | 40.3 °F | 60.2 °F | 50.25 in. |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| 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 |