Bethlehem, New Hampshire has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 31.4 °F (low) to 53.2 °F (high). Annual precipitation averages 41.4 Inches. Bethlehem is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Sep.11 - Sep. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 6.5 °F | 26.4 °F | 2.42 in. |
| February | 7.7 °F | 29.7 °F | 2.23 in. |
| March | 16.8 °F | 38.8 °F | 2.58 in. |
| April | 29.0 °F | 51.8 °F | 3.2 in. |
| May | 40.5 °F | 65.6 °F | 3.83 in. |
| June | 49.6 °F | 73.5 °F | 4.28 in. |
| July | 54.2 °F | 77.7 °F | 4.44 in. |
| August | 52.3 °F | 76.1 °F | 4.21 in. |
| September | 45.2 °F | 69.0 °F | 3.49 in. |
| October | 35.2 °F | 55.6 °F | 4.27 in. |
| November | 25.2 °F | 42.9 °F | 3.03 in. |
| December | 14.2 °F | 31.5 °F | 3.43 in. |
| Annual | 31.4 °F | 53.2 °F | 41.41 in. |
| Average First Frost Date | Sep.11 - Sep. 20 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | Over 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 |