The natural air conditioning that always has been one of the Bay Area’s main selling points will continue to cool off the region through the weekend, and National Weather Service forecasters believe it may also be mixed with a rare late-summer spate of rain.
There just won’t be much of it.
“The best chances of it are in the North Bay,” meteorologist David King said. “Even then, it won’t be a substantial rain. It might wet the sidewalks.”
The cool air is coming from the normal return of a deeper marine layer and the formation of stratus clouds 1,000 feet above the surface, King said. The result is that the fog is thicker and lasts longer, and the sun’s heat has a thicker area to penetrate.
Temperatures were not expected to get past 84 degrees anywhere in the Bay Area on Thursday, with the inland region again being the warmest place to be. San Jose was expected to get to 75, Oakland to 67, San Francisco to 63 and Monterey to 62.
The rain was expected to arrive Saturday night or Sunday morning, when the cold upper-level trough pushing down from the Bay of Alaska reaches the northern part of the state. King said some elevated areas in the North Bay might see one-tenth of an inch of rain, although some pockets of the storm could dump as much as a quarter-inch.
Some rain may fall in Alameda and Contra Costa Counties, as well as in the South Bay, King said.
“It’s what we call a nice helpful rain,” King said. “But it’s nothing that’s going to allow us to forget about fire season or anything that’s gonna drench us.”
Areas of the Dixie and Caldor fires are expected to be hit with some of the rain, and forecasters said areas of the northern state could get as much as three-quarters of an inch. The weather service said there was a small chance at least one-tenth of an inch will fall on areas of the Caldor Fire near the El Dorado National Forest.
Any rain to fall on the Dixie and Caldor fires would mark the second time this month that Mother Nature has offered a hand with both. Small amounts of rain fell on Sept. 9 and 10, but that rain also came with lightning, which created several other small spot fires.
The system was not expected to touch the KNP Complex Fire in the Sequoia National Forest, where temperatures are expected to peak in the low 60s over the weekend amid sunny, clear skies.
No lightning was expected with this storm system.
“We’re not anticipating this to be a thunderstorm-creating event,” meteorologist Roger Gass said. “It’s gonna be cold and damp.”
It also won’t stick around a long time, making way for a brief warmup: By Monday, clear skies and temperatures in the upper 80s and low 90s are expected. Patchy clouds are anticipated to return to the sky on Tuesday.
