Half Moon Bay Hits 80 Degrees While San Francisco Shivers Through Record Cold

San Francisco is experiencing some of its coldest winter temperatures in more than a century, yet just 30 miles away, a coastal town saw summer-like heat.

The National Weather Service Bay Area reported that El Granada, near Half Moon Bay, reached 80 degrees on Thursday, December 11. That high stood in stark contrast to temperatures across the rest of the Bay Area, which hovered mostly in the low to mid-50s. In some parts of the region, such as Milpitas, daytime highs failed to rise above 48.

Downtown San Francisco has recorded some of the coldest monthly temperatures since early weather records began. According to the National Weather Service, recent mornings have dropped into the low 40s, with afternoon highs struggling to get past the mid-50s. The NWS noted that the city broke a downtown record for the coldest December temperature in over a hundred years earlier this month.

Meteorologists attribute this unusual cold snap to dense tule fog drifting in from California’s Central Valley. This fog, common in winter months, traps cold air near the surface and suppresses temperature gains across much of the Bay Area. The fog has been unusually persistent this year, and forecasters say the region may not see warmer temperatures until around Christmas.

But not all parts of the region are equally affected. Unlike the inland valleys and lower elevations, the Half Moon Bay coast benefits from local geography. The northern edge of the Santa Cruz Mountains acts as a natural barrier, shielding the area from the cold fog. That explains why El Granada saw an unusually high temperature of 80 degrees—about 13 degrees above the historical average for the day.

The anomaly nearly tied the all-time high for December 11 in the area, falling just one degree short of the record. The NWS shared a graphic on social media with a short caption: “OK, Half Moon Bay,” highlighting the temperature oddity amid a map dominated by colder readings.

Looking ahead, forecasters expect the region to warm slightly but remain well below seasonal norms. Highs into the next week are predicted to stay in the 60 to 65 degree range for much of the Bay, with continued chilly nights. Still, Half Moon Bay residents may enjoy a rare pocket of warmth, even as the rest of the region digs into its winter coats.

While temporary, the sharp contrast in temperatures underscores the Bay Area’s microclimates and the impact of regional atmospheric patterns. As cold grips the inland core, pockets along the coast may remain unseasonably mild. For now, places like El Granada offer a snapshot of summer in the middle of December.