Grafton, Massachusetts has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 3.8 °C (low) to 15.1 °C (high). Annual precipitation averages 1253 Millimeters. Grafton is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -8.7 °C | 1.6 °C | 97.28 mm |
| February | -7.9 °C | 3.1 °C | 86.36 mm |
| March | -3.6 °C | 7.3 °C | 117.35 mm |
| April | 2.2 °C | 14.3 °C | 111.76 mm |
| May | 8.1 °C | 20.2 °C | 89.66 mm |
| June | 13.2 °C | 24.7 °C | 106.68 mm |
| July | 16.4 °C | 27.7 °C | 96.01 mm |
| August | 15.6 °C | 26.9 °C | 103.89 mm |
| September | 11.2 °C | 23.2 °C | 100.33 mm |
| October | 4.9 °C | 16.6 °C | 124.97 mm |
| November | -0.4 °C | 10.4 °C | 98.04 mm |
| December | -5.2 °C | 4.7 °C | 120.65 mm |
| Annual | 3.8 °C | 15.1 °C | 1252.98 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |