Charlestown, New Hampshire has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 35.1 °F (low) to 57 °F (high). Annual precipitation averages 41.4 Inches. 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 | 10.8 °F | 30.5 °F | 2.8 in. |
| February | 11.9 °F | 33.8 °F | 2.37 in. |
| March | 20.9 °F | 41.9 °F | 2.88 in. |
| April | 32.8 °F | 55.4 °F | 3.17 in. |
| May | 43.8 °F | 67.9 °F | 3.42 in. |
| June | 53.3 °F | 76.7 °F | 3.91 in. |
| July | 58.7 °F | 82.0 °F | 4.03 in. |
| August | 56.6 °F | 80.4 °F | 3.86 in. |
| September | 48.9 °F | 73.2 °F | 3.68 in. |
| October | 37.3 °F | 59.5 °F | 4.7 in. |
| November | 28.1 °F | 47.0 °F | 3.14 in. |
| December | 18.6 °F | 35.3 °F | 3.47 in. |
| Annual | 35.1 °F | 57 °F | 41.43 in. |
| 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 : -15°F to -10°F |
| Plant Hardiness Zone - 2012 | Zone 5a : -20°F to -15°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |