Charlestown, Maryland has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 7.6 °C (low) to 18.2 °C (high). Annual precipitation averages 1216.7 Millimeters. Charlestown is located in USDA Plant Hardiness Zone 7b. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -4 °C | 5.5 °C | 87.12 mm |
| February | -3.5 °C | 6.9 °C | 73.41 mm |
| March | 0.3 °C | 11.4 °C | 108.71 mm |
| April | 6.3 °C | 17.5 °C | 96.52 mm |
| May | 11.6 °C | 22.9 °C | 98.81 mm |
| June | 16.8 °C | 27.8 °C | 117.86 mm |
| July | 19.7 °C | 30.3 °C | 116.08 mm |
| August | 18.8 °C | 29.4 °C | 107.44 mm |
| September | 15 °C | 25.8 °C | 114.81 mm |
| October | 8.2 °C | 19.3 °C | 106.68 mm |
| November | 2.8 °C | 13.2 °C | 83.31 mm |
| December | -1.2 °C | 7.8 °C | 105.92 mm |
| Annual | 7.6 °C | 18.2 °C | 1216.67 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 75-100 Days |
| Plant Hardiness Zone | Zone 7b : -15°C to -12.2°C |
| Plant Hardiness Zone - 2012 | Zone 7a : -17.8°C to -15°C |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |