‘Weak disturbance’ in Bay Area weather pattern to end stretch of sunny days, very cold nights

Sunny, clear and at times extremely cold weather continued to be on the Bay Area’s weather menu Monday, continuing a pattern that has gone mostly unchanged for longer than a week.

By late in the work week, there finally will be a variation, according to the National Weather Service.

“We’re going to have a weak disturbance coming in probably Thursday, maybe late Thursday into early Friday,” NWS meteorologist Karleisa Rogacheski said. “And then after that, the next real strong system arrives.”

That strong system is expected to drop rain throughout the region this weekend, with the heaviest falling in the North Bay. The East Bay may get as much as a half-inch and the South Bay a quarter-inch, according to the weather service.

Until then, there will be other subtle changes to the pattern

Rogacheski said a bit of onshore flow is expected to begin Monday, and “that should clear out the air somewhat” following a weekend that saw a Spare the Air alert on Sunday. The high pressure that has covered the region and created a bubble that has kept the pollution from escaping is expected to dissipate significantly Monday.

“Then it’s going to build back up on Tuesday and Wednesday, before we get that first weak disturbance,” Rogacheski said. “How much rain that brings will depend of if there is any juice with it.”

No air quality alert was in place on Monday, though the Bay Area Air Quality Management District’s forecast called for moderately healthy air in most areas and air that could be unhealthy for those with respiratory or other conditions in the central part of the Bay Area and in the Santa Clara Valley.

The rain from the first disturbance is expected to be more like drizzle and is expected mostly to fall on areas in the North Bay, according to the weather service. The rest of the region is not expected to see rain until the weekend.

The change in the pattern also is expected to bring a farewell to the frigid temperatures that have dotted the region overnight. A frost advisory was in effect from midnight to 9 a.m. Monday in the southern Salinas Valley, and will be in effect again Tuesday from midnight to 9 a.m. in southern Monterey County and areas of the East Bay and South Bay interior regions. Overnight temperatures are expected to drop into the mid-to-low 30s.

Expected to arrive with the new pattern is high surf. The weather service said there is a possibility that waves will be higher than 10 feet along the coast next weekend and could combine with king tides to cause flooding issues in certain areas.

“There will be larger waves coming through,” Rogacheski said. “We’re keeping an eye on it, and we’ll have a better idea as we get closer to the weekend.”