Charlestown, New Hampshire has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 1.7 °C (low) to 13.9 °C (high). Annual precipitation averages 1052.3 Millimeters. Charlestown is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -11.8 °C | -0.8 °C | 71.12 mm |
| February | -11.2 °C | 1 °C | 60.2 mm |
| March | -6.2 °C | 5.5 °C | 73.15 mm |
| April | 0.4 °C | 13 °C | 80.52 mm |
| May | 6.6 °C | 19.9 °C | 86.87 mm |
| June | 11.8 °C | 24.8 °C | 99.31 mm |
| July | 14.8 °C | 27.8 °C | 102.36 mm |
| August | 13.7 °C | 26.9 °C | 98.04 mm |
| September | 9.4 °C | 22.9 °C | 93.47 mm |
| October | 2.9 °C | 15.3 °C | 119.38 mm |
| November | -2.2 °C | 8.3 °C | 79.76 mm |
| December | -7.4 °C | 1.8 °C | 88.14 mm |
| Annual | 1.7 °C | 13.9 °C | 1052.32 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5b : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |