Westerly, Rhode Island has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 5.9 °C (low) to 15.2 °C (high). Annual precipitation averages 1211.3 Millimeters. Westerly is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -5.8 °C | 3.5 °C | 99.31 mm |
| February | -4.9 °C | 4.4 °C | 86.36 mm |
| March | -1.1 °C | 7.9 °C | 125.73 mm |
| April | 3.9 °C | 13.3 °C | 114.81 mm |
| May | 9.2 °C | 18.4 °C | 88.9 mm |
| June | 14.6 °C | 23.4 °C | 95.5 mm |
| July | 17.9 °C | 26.8 °C | 76.71 mm |
| August | 17.2 °C | 26.2 °C | 92.46 mm |
| September | 13.4 °C | 23.1 °C | 90.42 mm |
| October | 7.3 °C | 17.2 °C | 118.62 mm |
| November | 1.9 °C | 11.7 °C | 101.85 mm |
| December | -2.3 °C | 6.7 °C | 120.65 mm |
| Annual | 5.9 °C | 15.2 °C | 1211.32 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 7a : -17.8°C to -15°C |
| Plant Hardiness Zone - 2012 | Zone 7a : -17.8°C to -15°C |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |