Hallowell, Maine has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 2.2 °C (low) to 13.1 °C (high). Annual precipitation averages 1185.7 Millimeters. Hallowell is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -11.8 °C | -1.3 °C | 88.39 mm |
| February | -10.9 °C | 0.4 °C | 75.44 mm |
| March | -5.4 °C | 5.1 °C | 93.98 mm |
| April | 0.6 °C | 12 °C | 105.92 mm |
| May | 6.6 °C | 18.3 °C | 86.87 mm |
| June | 11.9 °C | 23.3 °C | 108.2 mm |
| July | 15.2 °C | 26.6 °C | 83.82 mm |
| August | 14.4 °C | 26.1 °C | 88.14 mm |
| September | 10.3 °C | 21.9 °C | 99.06 mm |
| October | 4.2 °C | 14.9 °C | 136.14 mm |
| November | -1.3 °C | 8.2 °C | 111.51 mm |
| December | -7.2 °C | 2.1 °C | 108.2 mm |
| Annual | 2.2 °C | 13.1 °C | 1185.67 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5b : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |