Charleston, Maine has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 0.4 °C (low) to 12.1 °C (high). Annual precipitation averages 1141.2 Millimeters. Charleston is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around May 11 - May 20 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -14.4 °C | -3.2 °C | 84.33 mm |
| February | -13.6 °C | -1.3 °C | 69.85 mm |
| March | -7.6 °C | 3.8 °C | 84.84 mm |
| April | -0.9 °C | 11 °C | 95.5 mm |
| May | 5.2 °C | 18.2 °C | 92.46 mm |
| June | 10.6 °C | 23 °C | 112.01 mm |
| July | 13.8 °C | 26.1 °C | 90.42 mm |
| August | 12.8 °C | 25.5 °C | 90.68 mm |
| September | 8.3 °C | 21.1 °C | 93.98 mm |
| October | 2.4 °C | 13.7 °C | 123.19 mm |
| November | -2.7 °C | 6.7 °C | 101.85 mm |
| December | -9.2 °C | 0.3 °C | 102.11 mm |
| Annual | 0.4 °C | 12.1 °C | 1141.22 mm |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 11 - May 20 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5a : -28.9°C to -26.1°C |
| Plant Hardiness Zone - 2012 | Zone 4b : -31.7°C to -28.9°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |