| 2023 Hardiness Zone: | Zone 5b: -15°F to -10°F |
| 2012 Hardiness Zone: | Zone 5a: -20°F to -15°F Zone 5b: -15°F to -10°F |
| 1990 Hardiness Zone: | Zone 5a: -20F to -15F |
| Average First Frost Date: | Oct. 11 - Oct. 20 |
| Average Last Frost Date: | May 11 - May 20 |
| Koppen-Geiger Climate Zone: | Dfb - Humid Continental Mild Summer, Wet All Year |
| Ecoregion: | 58r - Sebago-Ossipee Hills and Plains |
| Heat Zone Days: | Rare Over 86°F |
Annual Climate Data for ZIP Code 03809 - Alton, NH | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Annual |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg Min Temp (°F) | 12 | 12 | 22 | 32 | 43 | 53 | 58 | 56 | 49 | 38 | 30 | 19 | 35 |
| Avg Max Temp (°F) | 29 | 32 | 41 | 54 | 66 | 75 | 80 | 78 | 69 | 58 | 45 | 33 | 55 |
| Avg Precip (In.) | 3.45 | 2.7 | 3.39 | 3.65 | 3.78 | 3.6 | 3.99 | 3.81 | 3.45 | 3.96 | 3.94 | 3.5 | 43.21 |