Westbrook, Maine has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 37.3 °F (low) to 56.4 °F (high). Annual precipitation averages 49.5 Inches. Westbrook is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 12.9 °F | 31.6 °F | 3.54 in. |
| February | 14.4 °F | 34.6 °F | 3.53 in. |
| March | 23.7 °F | 42.3 °F | 4.15 in. |
| April | 34.4 °F | 53.8 °F | 4.61 in. |
| May | 44.8 °F | 65.1 °F | 3.63 in. |
| June | 54.9 °F | 74.2 °F | 4.32 in. |
| July | 60.8 °F | 79.9 °F | 3.65 in. |
| August | 59.3 °F | 79.1 °F | 3.45 in. |
| September | 51.6 °F | 71.7 °F | 3.88 in. |
| October | 40.3 °F | 59.6 °F | 5.66 in. |
| November | 30.4 °F | 47.8 °F | 4.32 in. |
| December | 20.2 °F | 37.3 °F | 4.77 in. |
| Annual | 37.3 °F | 56.4 °F | 49.51 in. |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5b : -15°F to -10°F |
| Plant Hardiness Zone - 2012 | Zone 5b : -15°F to -10°F |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |