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Why the San Francisco Bay Area suddenly got so foggy this week

SF Gate logo SF Gate 6 days ago Amy Graff

It's a foggy soupy mess out there. The Bay Area has been covered in a thick wet blanket of gray all week, and yesterday in San Francisco the sun never broke through the drear.

This is actually a welcome change after the month of October that was marked by sunny skies, desiccating winds and extremely low relative humidity levels that left lips chapped and skin feeling dry.

But why the change? Meteorologist Drew Peterson with the National Weather Service explains a couple factors are at play.

First, a strong ocean breeze has picked up, and these onshore winds that blow water vapor off the Pacific Ocean inland are enhanced by a low-pressure system off the coast of Southern California. What's more, there's a high-pressure system over Northern California.

"That high pressure is going to compress any marine layer we do have toward the surface," says Peterson. "It gets smooshed."

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On Friday morning, the marine layer over San Francisco measured 1,500 feet-thick and the cloud cover spread all across the greater Bay Area. Peterson says Friday night is likely to be the foggiest night of the week.

On Saturday, atmospheric conditions will shift with the high-pressure system over Northern California moving east.

"It will still be foggy Saturday night into Sunday morning, but it starts to really thin out Sunday night into Monday," says Peterson. "It’s a change in the weather pattern into early next week that will cut back into the amount of fog we’re seeing."

Temperatures are chilly Friday morning, generally ranging from the mid-40s to low-50s in urban areas. Coastal areas will warm into the upper-50s to low-60s this afternoon and inland areas may hit the 70s. Temperatures will inch up over the weekend and especially on Monday. San Francisco is expected to see a high of 73 on Monday with inland areas in the low-80s.

Looking 10 days out, there is now rain in the forecast, and so far the month of November hasn't seen any rain.

"While the dry start is cause for concern, we’re still cautiously optimistic things might change into the winter," says Peterson. "With that said, California is a feast-or-famine state. Just looking at the climatological records, it wouldn’t be surprising if we were in for a year or two of dry weather."

Amy Graff is a digital editor for SFGATE. Email her weather photos and tips at agraff@sfgate.com.

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