Grafton, New York has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 2.8 °C (low) to 12.9 °C (high). Annual precipitation averages 1243.1 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 Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -10 °C | -1.2 °C | 81.53 mm |
| February | -9.3 °C | 0.4 °C | 68.83 mm |
| March | -5.1 °C | 4.8 °C | 88.9 mm |
| April | 1.2 °C | 12.6 °C | 95.5 mm |
| May | 7.6 °C | 19.2 °C | 105.16 mm |
| June | 12.6 °C | 23.4 °C | 129.79 mm |
| July | 15.1 °C | 26 °C | 121.16 mm |
| August | 14.3 °C | 24.9 °C | 115.82 mm |
| September | 10.3 °C | 21.2 °C | 112.27 mm |
| October | 4.7 °C | 14.4 °C | 132.33 mm |
| November | -1.3 °C | 7.5 °C | 91.44 mm |
| December | -6.3 °C | 1.6 °C | 100.33 mm |
| Annual | 2.8 °C | 12.9 °C | 1243.06 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 11 - May 20 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5b : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |