Dennis, Massachusetts has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 6.7 °C (low) to 14.4 °C (high). Annual precipitation averages 1223.3 Millimeters. Dennis is located in USDA Plant Hardiness Zone 7b. 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 | -4.1 °C | 3.6 °C | 109.98 mm |
| February | -3.6 °C | 4 °C | 93.22 mm |
| March | -0.8 °C | 6.8 °C | 118.62 mm |
| April | 3.9 °C | 11.6 °C | 111.76 mm |
| May | 9.1 °C | 16.9 °C | 86.61 mm |
| June | 14.2 °C | 21.9 °C | 87.63 mm |
| July | 18.2 °C | 25.8 °C | 72.14 mm |
| August | 17.8 °C | 25.3 °C | 84.58 mm |
| September | 14.3 °C | 22.2 °C | 106.17 mm |
| October | 8.7 °C | 16.5 °C | 117.86 mm |
| November | 3.6 °C | 11.3 °C | 103.12 mm |
| December | -0.7 °C | 6.7 °C | 131.57 mm |
| Annual | 6.7 °C | 14.4 °C | 1223.26 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 75-100 Days |
| Plant Hardiness Zone | Zone 7b : -15°C to -12.2°C |
| Plant Hardiness Zone - 2012 | Zone 7a : -17.8°C to -15°C |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |