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Thundershowers, Hail Storms Rumble Through San Francisco Bay Area

WALNUT CREEK (CBS SF) -- A low pressure system rolled across the San Francisco Bay Area Saturday afternoon triggering thundershowers and hail storms in several East Bay communities.

The National Weather Service radar at 2:30 p.m. showed several storm cells packing lightning, thunder and hail streaming through the East Bay.

Many residents took to social media, posting photos and videos of the brief, intense downpours.

The weather service issued an Urban and Small Stream Flood Advisory for the East Bay until 5:30 p.m. It was for poor drainage areas in central Alameda County, central Contra Costa County and north central Santa Clara County.

"Excessive runoff from heavy rainfall will cause flooding of small creeks and streams, urban areas, highways, streets and underpasses as
well as other drainage areas and low lying spots," the weather service warned. "In hilly terrain there are hundreds of low water crossings which are potentially dangerous in heavy rain. Do not attempt to cross flooded roads. Find an alternate route."

A high pressure system that was camped over the Bay Area for several days last week, triggering record high temperatures, moved eastward late Thursday allowing the low pressure system to follow in its wake.

Temperatures tumbled by 10 degrees or more by Saturday and unstable air moved in, bringing with it brief intense rainshowers and lightning.

"For what it's worth, latest lightning detection networks are already picking up some lightning near the upper low," weather service forecasters said on Friday. "Thunderstorm chances look more likely on Saturday as the colder core upper low moves through. Best chance for thunderstorms will be over the North and East Bay Saturday and early Saturday night."

When it comes to rainshowers, forecasters said the North Bay could received 1/4 to 1/2 inches by the time the showers move through.

While there have been showers in the Bay Area in April and May, they have fallen far short of making up for the deficit rolled up by the first February without rain since 1864.

Lightning brings with it the threat of wildfires.

Calfire was already reporting increased wildfire this year. From January 1, 2020 through May 24, 2020, state officials said there had been 1,506 fires that have burned 1,967 acres. In comparson from January 1, 2019 through May 24, 2019, there were 884 fires with 1,677 acres.

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