Williamstown, New Jersey has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 7.2 °C (low) to 18.2 °C (high). Annual precipitation averages 1205.2 Millimeters. Williamstown is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -4.3 °C | 5.3 °C | 96.77 mm |
| February | -3.6 °C | 6.7 °C | 73.15 mm |
| March | 0.1 °C | 10.9 °C | 115.57 mm |
| April | 5.8 °C | 17.7 °C | 88.14 mm |
| May | 10.9 °C | 23.2 °C | 95.25 mm |
| June | 16.3 °C | 28.2 °C | 107.44 mm |
| July | 19.3 °C | 30.4 °C | 122.43 mm |
| August | 18.4 °C | 29.5 °C | 121.16 mm |
| September | 14.7 °C | 25.8 °C | 103.38 mm |
| October | 7.8 °C | 19.3 °C | 97.54 mm |
| November | 2.2 °C | 13.3 °C | 77.98 mm |
| December | -1.5 °C | 7.9 °C | 106.43 mm |
| Annual | 7.2 °C | 18.2 °C | 1205.24 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 75-100 Days |
| Plant Hardiness Zone | Zone 7a : -17.8°C to -15°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |