Marlborough, New Hampshire has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 1.6 °C (low) to 13.7 °C (high). Annual precipitation averages 1190 Millimeters. 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 | -11.6 °C | -0.8 °C | 82.04 mm |
| February | -10.9 °C | 1 °C | 71.88 mm |
| March | -6.2 °C | 5.5 °C | 85.6 mm |
| April | 0.3 °C | 13.2 °C | 88.39 mm |
| May | 6.2 °C | 19.8 °C | 97.28 mm |
| June | 11.4 °C | 24.4 °C | 112.27 mm |
| July | 14.4 °C | 27.3 °C | 115.82 mm |
| August | 13.2 °C | 26.4 °C | 110.24 mm |
| September | 8.8 °C | 22.2 °C | 109.47 mm |
| October | 3.1 °C | 15.2 °C | 126.24 mm |
| November | -2.3 °C | 8.3 °C | 89.41 mm |
| December | -7.3 °C | 2.4 °C | 101.35 mm |
| Annual | 1.6 °C | 13.7 °C | 1189.99 mm |
| 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 : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |