Williamstown, Pennsylvania has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 40.4 °F (low) to 60.3 °F (high). Annual precipitation averages 51 Inches. Williamstown is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 19.0 °F | 35.4 °F | 3.53 in. |
| February | 20.5 °F | 37.9 °F | 2.83 in. |
| March | 28.3 °F | 46.8 °F | 4.08 in. |
| April | 38.8 °F | 60.3 °F | 4.27 in. |
| May | 48.7 °F | 70.4 °F | 4.34 in. |
| June | 57.5 °F | 78.6 °F | 4.86 in. |
| July | 61.3 °F | 83.3 °F | 4.83 in. |
| August | 59.6 °F | 81.8 °F | 4.59 in. |
| September | 52.6 °F | 75.0 °F | 5.2 in. |
| October | 41.6 °F | 63.2 °F | 4.66 in. |
| November | 32.3 °F | 50.5 °F | 3.85 in. |
| December | 24.9 °F | 40.1 °F | 3.97 in. |
| Annual | 40.4 °F | 60.3 °F | 51.01 in. |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6b : -5°F to 0°F |
| Plant Hardiness Zone - 2012 | Zone 6b : -5°F to 0°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |