Durham, Connecticut has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 5 °C (low) to 15.9 °C (high). Annual precipitation averages 1315.7 Millimeters. Durham is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -7.1 °C | 2.6 °C | 98.55 mm |
| February | -6.3 °C | 4 °C | 85.34 mm |
| March | -2.1 °C | 8.3 °C | 116.59 mm |
| April | 3.4 °C | 15.1 °C | 110.24 mm |
| May | 9 °C | 21 °C | 99.57 mm |
| June | 14.2 °C | 25.8 °C | 121.41 mm |
| July | 17.3 °C | 28.8 °C | 103.38 mm |
| August | 16.5 °C | 27.8 °C | 107.7 mm |
| September | 12.4 °C | 23.8 °C | 115.57 mm |
| October | 5.9 °C | 17.2 °C | 136.14 mm |
| November | 0.6 °C | 11.1 °C | 103.38 mm |
| December | -3.8 °C | 5.5 °C | 117.86 mm |
| Annual | 5 °C | 15.9 °C | 1315.73 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |