Seymour, Connecticut has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 41 °F (low) to 60.4 °F (high). Annual precipitation averages 51.5 Inches. 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 | 19.4 °F | 36.6 °F | 3.96 in. |
| February | 20.7 °F | 39.1 °F | 3.41 in. |
| March | 28.0 °F | 46.7 °F | 4.65 in. |
| April | 38.2 °F | 58.3 °F | 4.37 in. |
| May | 48.2 °F | 69.6 °F | 4.13 in. |
| June | 57.6 °F | 77.8 °F | 4.44 in. |
| July | 63.2 °F | 83.3 °F | 4.14 in. |
| August | 61.6 °F | 81.5 °F | 4.12 in. |
| September | 54.5 °F | 74.8 °F | 4.65 in. |
| October | 42.7 °F | 63.1 °F | 5.06 in. |
| November | 33.0 °F | 51.9 °F | 4.12 in. |
| December | 25.2 °F | 41.6 °F | 4.42 in. |
| Annual | 41 °F | 60.4 °F | 51.47 in. |
| 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 : -5°F to 0°F |
| Plant Hardiness Zone - 2012 | Zone 6b : -5°F to 0°F |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |