Williamstown, Massachusetts has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 36.8 °F (low) to 57 °F (high). Annual precipitation averages 43.7 Inches. 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. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 13.6 °F | 31.3 °F | 2.92 in. |
| February | 15.3 °F | 34.0 °F | 2.16 in. |
| March | 23.4 °F | 42.5 °F | 2.79 in. |
| April | 34.6 °F | 56.2 °F | 3.43 in. |
| May | 45.2 °F | 67.9 °F | 3.49 in. |
| June | 54.0 °F | 76.2 °F | 4.46 in. |
| July | 58.7 °F | 80.4 °F | 5.05 in. |
| August | 57.0 °F | 78.7 °F | 4.29 in. |
| September | 50.0 °F | 71.9 °F | 4.35 in. |
| October | 39.0 °F | 59.8 °F | 4.21 in. |
| November | 29.7 °F | 47.8 °F | 3.35 in. |
| December | 21.0 °F | 36.9 °F | 3.2 in. |
| Annual | 36.8 °F | 57 °F | 43.7 in. |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5b : -15°F to -10°F |
| Plant Hardiness Zone - 2012 | Zone 5b : -15°F to -10°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |