Charlestown, Rhode Island has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 6.7 °C (low) to 15 °C (high). Annual precipitation averages 1246.9 Millimeters. Charlestown 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 | -4.6 °C | 3.6 °C | 102.87 mm |
| February | -3.9 °C | 4.4 °C | 91.19 mm |
| March | -0.8 °C | 7.6 °C | 132.33 mm |
| April | 4.2 °C | 12.9 °C | 117.35 mm |
| May | 9.3 °C | 18.2 °C | 88.65 mm |
| June | 14.6 °C | 23.1 °C | 95.25 mm |
| July | 18.1 °C | 26.3 °C | 77.98 mm |
| August | 17.7 °C | 25.9 °C | 96.01 mm |
| September | 14.6 °C | 22.8 °C | 94.23 mm |
| October | 8.9 °C | 17.2 °C | 120.65 mm |
| November | 3.5 °C | 11.7 °C | 106.17 mm |
| December | -1 °C | 6.7 °C | 124.21 mm |
| Annual | 6.7 °C | 15 °C | 1246.89 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 | Moderate Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |