Mystic, Connecticut has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 6.5 °C (low) to 15.2 °C (high). Annual precipitation averages 1196.6 Millimeters. Mystic is located in USDA Plant Hardiness Zone 7a. 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 | -5 °C | 3.6 °C | 96.77 mm |
| February | -4.4 °C | 4.6 °C | 80.77 mm |
| March | -1 °C | 8 °C | 121.16 mm |
| April | 4.1 °C | 13.3 °C | 111.25 mm |
| May | 9.3 °C | 18.5 °C | 90.42 mm |
| June | 14.6 °C | 23.5 °C | 94.23 mm |
| July | 18.1 °C | 26.6 °C | 77.98 mm |
| August | 17.8 °C | 26.1 °C | 97.54 mm |
| September | 14.1 °C | 22.9 °C | 101.6 mm |
| October | 8.4 °C | 17.2 °C | 113.54 mm |
| November | 3.2 °C | 11.8 °C | 95.76 mm |
| December | -1.4 °C | 6.8 °C | 115.57 mm |
| Annual | 6.5 °C | 15.2 °C | 1196.59 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 7a : -17.8°C to -15°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |