The National Weather Service issued the watch, which began Friday afternoon and will continue until 3 p.m. Saturday.
During that time, between 2 and 5 inches of rain are anticipated, forecasters said.
Over the past three days, Lake County has seen a large amount of rainfall.
Rainfall totals in inches for the 72-hour period ending at 2 a.m. Saturday are as follows:
— Hidden Valley Lake: 2.59.
— Indian Valley Reservoir: 1.50.
— Knoxville Creek: 2.32.
— Lake Pillsbury: 4.13.
— Lower Lake: 2.41.
— Lyons Valley: 2.87.
— Middletown: 1.21.
— Upper Lake: 2.95.
— Whispering Pines: 4.20.
In addition to rising water levels in creeks, streams and the lake, the flood watch warns of increased danger of rock and mudslides.
Due to the heavy weather, Pacific Gas and Electric reported that it had positioned crews and resources across its service area “to support the safe and swift response repair to damage and restore power outages that may result from the forecasted heavy rain and strong winds.”
PG&E Meteorologist Evan Duffey called it a “fast-moving storm that will also deliver significant precipitation and widespread damaging winds.”
The company has prestaged power poles, powerlines, transformers and other electric equipment at yards throughout its service area to make equipment repairs and restore power to affected areas safely and as quickly as possible.
The National Weather Service reported that high winds are expected along with rain through the weekend.
Temperatures this weekend will be in the 40s during the day and the 30s at night.
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