| 2023 Hardiness Zone: | Zone 7a: 0°F to 5°F |
| 2012 Hardiness Zone: | Zone 6b: -5°F to 0°F Zone 7a: 0°F to 5°F |
| 1990 Hardiness Zone: | Zone 6a: -10F to -5F |
| Average First Frost Date: | October 21 - 31 |
| Average Last Frost Date: | April 21 - 30 |
| Koppen-Geiger Climate Zone: | Dfb - Humid Continental Mild Summer, Wet All Year |
| Ecoregion: | 59c - Southern New England Coastal Plains and Hills |
| Heat Zone Days: | Rare Over 86°F |
Annual Climate Data for ZIP Code 06475 - Old Saybrook, CT | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Annual |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg Min Temp (°F) | 18 | 20 | 28 | 35 | 45 | 55 | 61 | 60 | 53 | 41 | 33 | 24 | 39 |
| Avg Max Temp (°F) | 38 | 40 | 48 | 58 | 68 | 76 | 82 | 81 | 74 | 64 | 53 | 43 | 60 |
| Avg Precip (In.) | 4.46 | 3.47 | 4.43 | 4.39 | 3.96 | 3.84 | 3.64 | 4.4 | 3.95 | 4.18 | 4.53 | 4.24 | 49.48 |