Brentwood, New Hampshire has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 37.3 °F (low) to 58.4 °F (high). Annual precipitation averages 47 Inches. Brentwood is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 15.0 °F | 33.6 °F | 3.33 in. |
| February | 16.6 °F | 36.4 °F | 3.23 in. |
| March | 24.4 °F | 44.0 °F | 4.24 in. |
| April | 34.4 °F | 56.7 °F | 4.22 in. |
| May | 44.5 °F | 67.4 °F | 3.79 in. |
| June | 54.2 °F | 76.6 °F | 4.15 in. |
| July | 59.8 °F | 82.1 °F | 3.6 in. |
| August | 58.1 °F | 80.9 °F | 3.58 in. |
| September | 50.4 °F | 73.5 °F | 3.88 in. |
| October | 38.9 °F | 61.1 °F | 4.81 in. |
| November | 30.1 °F | 49.7 °F | 3.77 in. |
| December | 21.6 °F | 38.8 °F | 4.37 in. |
| Annual | 37.3 °F | 58.4 °F | 46.97 in. |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 6a : -10°F to -5°F |
| Plant Hardiness Zone - 2012 | Zone 6a : -10°F to -5°F |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |