(CBS SF) -- Rain and thunderstorms are back in the forecast as a low-pressure system builds off the coast of San Francisco.
The system is preempted by the visibility of wispy, thin cirrus clouds 16,000 to 22,000 feet in elevation which typically run in advancement of a frontal system or a tropical cyclone.
"It is a good indication that the weather will be deteriorating," said KPIX Morning Anchor Roberta Gonzales.
The frontal system has been hanging off the coast of San Francisco for the past 48 hours. The rotation around the core of low pressure is already visible.
The wrap-around moisture means the Bay Area can expect a chance of showers in the forecast by Wednesday evening into Thursday morning, along with the possibility of a thunderstorm as this area of low pressure taps into subtropical moisture.
The High Sierra will also see some thunderstorms in the forecast as a flash flood watch goes into effect beginning at noon Tuesday until 9 p.m.
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