Williamstown, Kentucky has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 7.4 °C (low) to 18.4 °C (high). Annual precipitation averages 1155.7 Millimeters. 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 | -4.7 °C | 4.5 °C | 82.55 mm |
| February | -3.2 °C | 7.1 °C | 73.66 mm |
| March | 1.1 °C | 12.2 °C | 106.17 mm |
| April | 6.9 °C | 19 °C | 117.35 mm |
| May | 12.4 °C | 23.9 °C | 124.46 mm |
| June | 16.6 °C | 28.2 °C | 123.7 mm |
| July | 18.7 °C | 30.1 °C | 107.44 mm |
| August | 18.2 °C | 29.6 °C | 82.04 mm |
| September | 14.4 °C | 26.6 °C | 81.03 mm |
| October | 7.9 °C | 20.5 °C | 81.79 mm |
| November | 2 °C | 12.7 °C | 81.79 mm |
| December | -2.1 °C | 6.8 °C | 93.73 mm |
| Annual | 7.4 °C | 18.4 °C | 1155.71 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 75-100 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |