Stewartstown, New Hampshire has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 29.4 °F (low) to 48.2 °F (high). Annual precipitation averages 50.1 Inches. Stewartstown is located in USDA Plant Hardiness Zone 4a. The growing season typically runs from the last frost around May 21 - May 31 through the first frost around Sep.11 - Sep. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 1.8 °F | 20.6 °F | 3.59 in. |
| February | 3.4 °F | 23.1 °F | 3.05 in. |
| March | 12.9 °F | 32.2 °F | 3.64 in. |
| April | 29.0 °F | 46.7 °F | 3.65 in. |
| May | 39.0 °F | 60.3 °F | 4.51 in. |
| June | 48.7 °F | 69.2 °F | 5.2 in. |
| July | 54.0 °F | 73.4 °F | 4.81 in. |
| August | 51.9 °F | 72.1 °F | 4.56 in. |
| September | 44.6 °F | 65.0 °F | 4.02 in. |
| October | 33.6 °F | 51.2 °F | 4.88 in. |
| November | 23.1 °F | 38.0 °F | 3.9 in. |
| December | 10.8 °F | 27.1 °F | 4.32 in. |
| Annual | 29.4 °F | 48.2 °F | 50.13 in. |
| Average First Frost Date | Sep.11 - Sep. 20 |
| Average Last Frost Date | May 21 - May 31 |
| Average Days With Frost | Over 180 Days |
| Plant Hardiness Zone | Zone 4a : -30°F to -25°F |
| Plant Hardiness Zone - 2012 | Zone 3b : -35°F to -30°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |