Marlborough, New Hampshire has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 34.9 °F (low) to 56.7 °F (high). Annual precipitation averages 46.9 Inches. Marlborough is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around May 11 - May 20 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 11.2 °F | 30.6 °F | 3.23 in. |
| February | 12.4 °F | 33.8 °F | 2.83 in. |
| March | 20.9 °F | 41.9 °F | 3.37 in. |
| April | 32.6 °F | 55.8 °F | 3.48 in. |
| May | 43.2 °F | 67.6 °F | 3.83 in. |
| June | 52.6 °F | 76.0 °F | 4.42 in. |
| July | 57.9 °F | 81.1 °F | 4.56 in. |
| August | 55.7 °F | 79.5 °F | 4.34 in. |
| September | 47.8 °F | 71.9 °F | 4.31 in. |
| October | 37.5 °F | 59.4 °F | 4.97 in. |
| November | 27.8 °F | 46.9 °F | 3.52 in. |
| December | 18.9 °F | 36.3 °F | 3.99 in. |
| Annual | 34.9 °F | 56.7 °F | 46.85 in. |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 11 - May 20 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5b : -15°F to -10°F |
| Plant Hardiness Zone - 2012 | Zone 5a : -20°F to -15°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |