Bristol, Maine has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 4.1 °C (low) to 12 °C (high). Annual precipitation averages 1252.7 Millimeters. Bristol is located in USDA Plant Hardiness Zone 6a. 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 | -7.3 °C | 0.2 °C | 100.58 mm |
| February | -6.9 °C | 1.1 °C | 91.69 mm |
| March | -3.1 °C | 4.4 °C | 114.05 mm |
| April | 1.8 °C | 10.1 °C | 111 mm |
| May | 6.8 °C | 15.5 °C | 93.73 mm |
| June | 11.7 °C | 20.2 °C | 107.7 mm |
| July | 14.8 °C | 23.4 °C | 86.36 mm |
| August | 14.8 °C | 23.4 °C | 78.49 mm |
| September | 11.7 °C | 19.9 °C | 103.63 mm |
| October | 6.7 °C | 13.9 °C | 129.79 mm |
| November | 1.7 °C | 8.6 °C | 114.05 mm |
| December | -3.7 °C | 3.4 °C | 121.67 mm |
| Annual | 4.1 °C | 12 °C | 1252.74 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 6a : -23.3°C to -20.6°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |