Seymour, Connecticut has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5 °C (low) to 15.8 °C (high). Annual precipitation averages 1307.3 Millimeters. Seymour 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 °C | 2.6 °C | 100.58 mm |
| February | -6.3 °C | 3.9 °C | 86.61 mm |
| March | -2.2 °C | 8.2 °C | 118.11 mm |
| April | 3.4 °C | 14.6 °C | 111 mm |
| May | 9 °C | 20.9 °C | 104.9 mm |
| June | 14.2 °C | 25.4 °C | 112.78 mm |
| July | 17.3 °C | 28.5 °C | 105.16 mm |
| August | 16.4 °C | 27.5 °C | 104.65 mm |
| September | 12.5 °C | 23.8 °C | 118.11 mm |
| October | 5.9 °C | 17.3 °C | 128.52 mm |
| November | 0.6 °C | 11.1 °C | 104.65 mm |
| December | -3.8 °C | 5.3 °C | 112.27 mm |
| Annual | 5 °C | 15.8 °C | 1307.34 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 | Dfa - Humid Continental Hot Summers With Year Around Precipitation |