Williamstown, New York has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 2.3 °C (low) to 13.1 °C (high). Annual precipitation averages 1357.9 Millimeters. Williamstown is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -11.1 °C | -1.6 °C | 124.71 mm |
| February | -10.4 °C | -0.3 °C | 104.65 mm |
| March | -6.1 °C | 4.3 °C | 101.09 mm |
| April | 0.6 °C | 12.3 °C | 100.08 mm |
| May | 6.9 °C | 19.6 °C | 109.22 mm |
| June | 12.1 °C | 24.1 °C | 105.41 mm |
| July | 14.7 °C | 26.5 °C | 106.43 mm |
| August | 13.8 °C | 25.9 °C | 108.71 mm |
| September | 9.8 °C | 22.1 °C | 113.54 mm |
| October | 4.2 °C | 14.8 °C | 138.68 mm |
| November | -1 °C | 7.8 °C | 116.84 mm |
| December | -6.5 °C | 1.7 °C | 128.52 mm |
| Annual | 2.3 °C | 13.1 °C | 1357.88 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5b : -26.1°C to -23.3°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 |