Grafton, New Hampshire has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 31.7 °F (low) to 54 °F (high). Annual precipitation averages 41.7 Inches. Grafton is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around May 11 - May 20 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 7.3 °F | 27.7 °F | 2.92 in. |
| February | 8.1 °F | 30.8 °F | 2.34 in. |
| March | 17.5 °F | 39.1 °F | 3.07 in. |
| April | 29.5 °F | 52.4 °F | 3.2 in. |
| May | 41.5 °F | 65.4 °F | 3.47 in. |
| June | 49.7 °F | 73.6 °F | 4.05 in. |
| July | 54.3 °F | 78.4 °F | 4.04 in. |
| August | 52.4 °F | 76.9 °F | 3.57 in. |
| September | 44.8 °F | 69.6 °F | 3.48 in. |
| October | 34.4 °F | 56.3 °F | 4.84 in. |
| November | 25.6 °F | 44.3 °F | 3.2 in. |
| December | 15.4 °F | 33.1 °F | 3.47 in. |
| Annual | 31.7 °F | 54 °F | 41.65 in. |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 11 - May 20 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5a : -20°F to -15°F |
| Plant Hardiness Zone - 2012 | Zone 4b : -25°F to -20°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |