The official National Weather Service forecast for Sunapee — 43.3876°N, 72.0879°W, 3.9 miles from I-89.
| Sullivan County | J | F | M | A | M | J | J | A | S | O | N | D | Year |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high °F | 29 | 33 | 41 | 54 | 67 | 75 | 80 | 78 | 71 | 58 | 45 | 34 | 55 |
| Avg low °F | 11 | 12 | 20 | 31 | 42 | 51 | 57 | 55 | 47 | 37 | 27 | 18 | 34 |
| Precip in | 3.2 | 2.8 | 3.3 | 3.7 | 3.9 | 4.6 | 4.5 | 4.1 | 3.8 | 4.9 | 3.3 | 4.1 | 46.2 |
1996–2025 normals for Sullivan County — the climate division Sunapee sits in. All-time county record high 95.0°F (2025-06-25); record low -31.1°F (1957-01-14). Source: NOAA / National Weather Service.