For some in Bay Area, rain may be mixed with occasional thunder, lightning

The return of rain to the Bay Area came relatively quietly as light showers scattered throughout the region and announced a change to a dry pattern that has made the wet stuff rare since Christmas.

More of the same was expected to continue into Wednesday, only with potentially a bit more noise and electricity.

“The shower activity is going to continue throughout the day,” National Weather Service meteorologist Lamont Bain said. “As it pertains to thunderstorm risk, there’s probably a 10-to-15 percent chance. There is a lot of instability between the upper low pressure and the lower air. That upper low is going to spin out there and not move much, and that’s why the rain showers are going to be scattered throughout the day and why the best chances for thunder are out over the ocean.”

A low-pressure system off the Central Coast is continuing to drive the stormy weather and is proceeding north. The heaviest rain came in the Santa Cruz Mountains, with more than 1½ inches falling at Mt. Umunhum, Ben Lomond and Loma Prieta in the 24 hours before 7 a.m. Wednesday.

Elsewhere, San Francisco received one-third of an inch, while Oakland and San Jose had a quarter-inch. Mount Diablo received about a half-inch but the cities in its shadow did not get much. Concord received just four-hundredths of an inch, the most of the nearby cities.

That same system will continue to trudge north on Wednesday, according to the weather service. As it does so, it is expected to weaken and the winds associated with Tuesday’s rain are expected to calm down. The weather service said the system also will carry with it lift, instability and moisture, the three elements needed for thunderstorms.

By Thursday, the rain from this low pressure system is expected to be finished. Another storm system then is expected to descend from the north over the weekend, bringing more rain.

Bain said the North Bay may see rain as early as Saturday morning but that that it’s more likely the rain won’t arrive there until later in the afternoon or early evening. He added that the entire region should see rain from the second system by late Saturday night into Sunday.

“Part of the weekend may be salvageable if you want to be outdoors,” Bain said. “The timing details will come more into focus over the weekend.”

The rain from the second storm is expected to last at least through Tuesday.