4,000-foot-deep marine layer brings wet weather to Bay Area

Bay Area residents close to the Pacific Ocean coastline will get the chance to experience some rare summer precipitation Friday morning as a low-pressure system brings drizzle and cooler temperatures to the region.

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Rick Canepa, a meteorologist at the National Weather Service, said measurable precipitation was detected across multiple parts of the Bay Area, including in downtown San Francisco with 0.02 inch, and parts of the Marin Headlands, Mount Tamalpais and Point Reyes, which received between 0.01 and 0.08 inch of precipitation as of 7 a.m. Friday morning.

Canepa said August is traditionally the “second driest” month of the year behind July, and the only precipitation expected this month is due to drizzle from coastal fog or the rare monsoonal storm strong enough to drop rain. 

But on Friday, a large marine layer 4,000 feet deep in some locations is keeping the region cool and contributing to the wet weather, Canepa said.

“Most locations, like right at closer to sea level, below 2,500 feet, are mostly in the 50s to about 60 degrees right now,” he said, explaining the light rain is partially the result of the “cooler air interacting with higher amount of water vapor.” 

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The National Weather Service reported “below normal” temperatures for the region on Friday in the forecast discussion.

“There’s really no warmth indicated at all anywhere, even at the highest points along the Santa Cruz Mountains,” he said. 

The classic “fogust” summer weather for the Bay Area does have a bright spot, as it may help mitigate the ongoing Timber Fire in Big Sur, which has burned 4,545 acres and is currently 7% contained with 1,842 personnel responding, according to Cal Fire. In a news release from the Los Padres National Forest, officials said coastal areas are expected to see “cooler and wetter conditions” for the next several days, although areas at higher elevations and further inland will still see more sunny and dry weather.