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5d ago

Marine Layer Deepens Across California as Beach Hazards Rise

A coastal trough is strengthening onshore flow, deepening low clouds and expanding drizzle while models point to a rapid inland warmup early next week.

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Downtown San Francisco briefly spiked to 89 degrees on June 11, but temperatures quickly fell back into the 60s as the marine layer returned. Since June 6, afternoon highs have been near or slightly below normal, while overnight lows have stayed relatively mild, a common signal of low clouds trapping heat near the surface.
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Overview

  • The cooling trend is underway midweek with a deepened marine layer producing widespread low clouds and patchy drizzle and forecasts calling for temperatures about 3–10°F below normal into the weekend.
  • National Weather Service products remain in effect for the coast, including a Coastal Flood Advisory and Beach Hazards Statement that warn of higher tides, strong rip currents, sneaker waves and up to about 1.8 feet of localized inundation.
  • Northern California is seeing a stronger Delta Breeze that is cooling valley highs into the 80s and bringing gusts around 20–30 mph in delta and valley corridors with an increased chance of isolated Sierra showers and afternoon thunderstorms Thursday and Friday.
  • Gusty onshore winds are expected to peak toward Friday and could reach advisory levels in elevated coastal and interior areas, which raises localized fire-weather concerns above the marine layer and will keep ocean hazards elevated even as air temperatures fall.
  • Local smoke from the Mateo Fire is already degrading air quality in parts of North County, and the pattern shift to a strong high early next week is forecast to compress the marine layer and drive a rapid inland warmup that could push valley temperatures well above normal.