Grafton, Vermont has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 0.7 °C (low) to 12.9 °C (high). Annual precipitation averages 1225.6 Millimeters. Grafton 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 | -12.5 °C | -1.6 °C | 88.65 mm |
| February | -12.1 °C | 0.1 °C | 73.41 mm |
| March | -7.4 °C | 4.5 °C | 95.76 mm |
| April | -0.8 °C | 11.9 °C | 98.55 mm |
| May | 5.7 °C | 19 °C | 102.62 mm |
| June | 10.8 °C | 23.6 °C | 117.6 mm |
| July | 13.4 °C | 26.4 °C | 108.71 mm |
| August | 12.4 °C | 25.6 °C | 103.38 mm |
| September | 7.9 °C | 21.7 °C | 102.87 mm |
| October | 1.8 °C | 14.2 °C | 130.05 mm |
| November | -3.2 °C | 7.6 °C | 97.03 mm |
| December | -8.2 °C | 1.3 °C | 106.93 mm |
| Annual | 0.7 °C | 12.9 °C | 1225.56 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 |