Williamstown, Vermont has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 32.6 °F (low) to 53.8 °F (high). Annual precipitation averages 40.9 Inches. 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 | 7.2 °F | 26.7 °F | 2.67 in. |
| February | 8.3 °F | 30.0 °F | 2.25 in. |
| March | 17.7 °F | 38.4 °F | 2.87 in. |
| April | 30.3 °F | 52.0 °F | 3.24 in. |
| May | 42.0 °F | 65.7 °F | 3.37 in. |
| June | 51.1 °F | 74.2 °F | 4.44 in. |
| July | 56.0 °F | 78.8 °F | 4.54 in. |
| August | 54.1 °F | 77.2 °F | 3.88 in. |
| September | 46.7 °F | 70.0 °F | 3.26 in. |
| October | 36.0 °F | 56.4 °F | 4.01 in. |
| November | 26.3 °F | 43.7 °F | 3.02 in. |
| December | 15.5 °F | 32.2 °F | 3.31 in. |
| Annual | 32.6 °F | 53.8 °F | 40.86 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 | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |