Charleston, Maine has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 32.7 °F (low) to 53.7 °F (high). Annual precipitation averages 44.9 Inches. 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 | 6.1 °F | 26.2 °F | 3.32 in. |
| February | 7.5 °F | 29.7 °F | 2.75 in. |
| March | 18.4 °F | 38.8 °F | 3.34 in. |
| April | 30.4 °F | 51.8 °F | 3.76 in. |
| May | 41.4 °F | 64.7 °F | 3.64 in. |
| June | 51.0 °F | 73.4 °F | 4.41 in. |
| July | 56.8 °F | 79.0 °F | 3.56 in. |
| August | 55.0 °F | 77.9 °F | 3.57 in. |
| September | 47.0 °F | 70.0 °F | 3.7 in. |
| October | 36.4 °F | 56.7 °F | 4.85 in. |
| November | 27.1 °F | 44.0 °F | 4.01 in. |
| December | 15.4 °F | 32.6 °F | 4.02 in. |
| Annual | 32.7 °F | 53.7 °F | 44.93 in. |
| 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 : -20°F to -15°F |
| Plant Hardiness Zone - 2012 | Zone 4b : -25°F to -20°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |