The official National Weather Service forecast for Half Moon Bay — 37.4635°N, 122.4286°W, population 21,688, 5.6 miles from I-280. Forecasts here are written by NWS MTR, this county’s forecast office.
| San Mateo County | J | F | M | A | M | J | J | A | S | O | N | D | Year |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high °F | 58 | 60 | 62 | 64 | 67 | 72 | 74 | 75 | 75 | 71 | 63 | 58 | 67 |
| Avg low °F | 43 | 43 | 44 | 45 | 48 | 51 | 54 | 54 | 54 | 50 | 46 | 43 | 48 |
| Precip in | 5.3 | 5.4 | 3.9 | 2.0 | 0.8 | 0.1 | 0.0 | 0.0 | 0.1 | 1.3 | 3.0 | 6.1 | 28.0 |
1996–2025 normals for San Mateo County — the climate division Half Moon Bay sits in. All-time county record high 105.0°F (2017-09-03); record low 19.0°F (1990-12-22). Source: NOAA / National Weather Service.