The official National Weather Service forecast for Chelsea — 42.3918°N, 71.0328°W, 1.1 miles from I-90.
| Suffolk County | J | F | M | A | M | J | J | A | S | O | N | D | Year |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high °F | 37 | 40 | 47 | 58 | 68 | 77 | 83 | 82 | 75 | 63 | 52 | 43 | 60 |
| Avg low °F | 21 | 22 | 29 | 38 | 48 | 57 | 64 | 62 | 55 | 44 | 35 | 26 | 42 |
| Precip in | 3.9 | 3.5 | 4.6 | 4.3 | 4.0 | 4.3 | 3.8 | 3.6 | 3.8 | 4.8 | 3.6 | 4.7 | 48.9 |
1996–2025 normals for Suffolk County — the climate division Chelsea sits in. All-time county record high 101.9°F (2025-06-25); record low -12.6°F (1957-01-15). Source: NOAA / National Weather Service.