Williamstown, Vermont has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 0.3 °C (low) to 12.1 °C (high). Annual precipitation averages 1037.9 Millimeters. Williamstown 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 | -13.8 °C | -2.9 °C | 67.82 mm |
| February | -13.2 °C | -1.1 °C | 57.15 mm |
| March | -7.9 °C | 3.6 °C | 72.9 mm |
| April | -0.9 °C | 11.1 °C | 82.3 mm |
| May | 5.6 °C | 18.7 °C | 85.6 mm |
| June | 10.6 °C | 23.4 °C | 112.78 mm |
| July | 13.3 °C | 26 °C | 115.32 mm |
| August | 12.3 °C | 25.1 °C | 98.55 mm |
| September | 8.2 °C | 21.1 °C | 82.8 mm |
| October | 2.2 °C | 13.6 °C | 101.85 mm |
| November | -3.2 °C | 6.5 °C | 76.71 mm |
| December | -9.2 °C | 0.1 °C | 84.07 mm |
| Annual | 0.3 °C | 12.1 °C | 1037.85 mm |
| 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 : -28.9°C to -26.1°C |
| Plant Hardiness Zone - 2012 | Zone 4b : -31.7°C to -28.9°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |