Westerly, Rhode Island has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 42.7 °F (low) to 59.4 °F (high). Annual precipitation averages 47.7 Inches. 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 | 21.5 °F | 38.3 °F | 3.91 in. |
| February | 23.1 °F | 39.9 °F | 3.4 in. |
| March | 30.0 °F | 46.2 °F | 4.95 in. |
| April | 39.1 °F | 55.9 °F | 4.52 in. |
| May | 48.6 °F | 65.2 °F | 3.5 in. |
| June | 58.2 °F | 74.1 °F | 3.76 in. |
| July | 64.2 °F | 80.2 °F | 3.02 in. |
| August | 63.0 °F | 79.2 °F | 3.64 in. |
| September | 56.1 °F | 73.5 °F | 3.56 in. |
| October | 45.2 °F | 62.9 °F | 4.67 in. |
| November | 35.4 °F | 53.0 °F | 4.01 in. |
| December | 27.8 °F | 44.0 °F | 4.75 in. |
| Annual | 42.7 °F | 59.4 °F | 47.69 in. |
| 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 : 0°F to 5°F |
| Plant Hardiness Zone - 2012 | Zone 7a : 0°F to 5°F |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |