Chance of rain, 'heavy downpours' head toward SF Bay Area

Clouds hang over San Francisco and the Bay Bridge on May 25. After a warm weekend, rain is expected to hit the San Francisco Bay Area on Monday, the weather service said.

After a warm and sunny weekend, chances of rain and thunderstorms are about to creep into the San Francisco Bay Area forecast, the National Weather Service said.

As an upper-level system originating from the Pacific approaches the coast of Southern California and gradually makes its way toward California's Central Coast on Monday morning, meteorologists expect a 10% to 20% probability of rain over Monterey and San Benito counties that will increase as the weather system moves north. Once it reaches the Bay Area, a 15% to 25% chance of isolated showers, as well as thunderstorms, are in the forecast across much of the region, with rain chances increasing to 20 to 30% by Monday night.

"We are going to see conditions become more unsettled," Roger Gass, a meteorologist for the weather service, said over the phone Sunday. "Many areas are expected to see less than a tenth of an inch of rainfall as a whole, and those chances are widespread across most of the region. However, wherever a shower does develop, we could see rainfall amounts approaching a quarter of an inch or greater, especially if thunderstorms do occur."

Those potential thunderstorms are most likely along the Central Coast, in Santa Cruz County and farther south, but they’ll be sporadic, Gass said. Chances of rain overall are expected to last until early Tuesday morning. Temperatures below the seasonal average, with lows in the mid-50s, are forecast to persist throughout the rest of the week.

After a warm weekend, unsettled weather returns early next week. From Monday into Tuesday there is a 15%-35% probability of rain showers & 15%-20% probability of thunderstorms across the region as an upper level low develops off of the central California coast. Stay tuned! #CAwx pic.twitter.com/dNOBjZ6L09

Bay Area storm systems aren't typical in June, but they can still happen, Gass explained.

"As we head into the summer months, the frequency of seeing storm systems that produce precipitation diminish," he said. "Usually, we’d see dry conditions prevail around this time of year, but it's not unheard of to see these systems that produce showers and thunderstorms."

People are encouraged to be mindful of the latest weather updates and take it slow on their commute, as storms could lead to hazardous travel conditions.

"With any thunderstorm, we can anticipate occasional lightning strikes and copious amounts of small hail, which can cause slick roadways," Gass said. "Brief heavy downpours and erratic gusty winds are also possible, but those are linked to stronger cells. We’re not expecting a widespread wind threat, but any storms that develop could produce some of those hazards."

Check with the weather service for more information.

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