As California braces for another round of atmospheric rivers and storms, Gov. Gavin Newsom on Wednesday declared a state of emergency to support storm response and relief efforts in 21 counties, including five in the greater Bay Area.

Storms are forecast to pummel the state through mid-March, and many areas are already grappling with flooding, power outages and damage from recent record rainfall and snow storms.

The emergency proclamation issued Wednesday to provide disaster response and relief includes San Francisco, San Mateo, Santa Clara, Santa Cruz and Monterey counties.

Last week, a state of emergency was issued for 13 counties statewide that included Sonoma County, and the governor activated the California Guard and State Operations Center.

Bay Area communities are preparing for high winds and possible flooding as an atmospheric river approaches the region with heavy rains on Thursday and Friday. A flood watch is in effect for the region from Thursday afternoon, March 9, through Sunday morning, March 12, and a wind advisory is in effect for the entire Bay Area and Central Coast Thursday afternoon through Friday afternoon.

Lingering rain will continue into the weekend with yet another atmospheric river expected next week, according to the National Weather Service.

"The state is working around the clock with local partners to deploy life-saving equipment and first responders to communities across California," Newsom said Wednesday. "With more dangerous storms on the horizon, we'll continue to mobilize every available resource to protect Californians."

San Mateo County

The County of San Mateo Department of Emergency Management cautioned residents to prepare for severe weather, recommending people sign up for emergency alerts, monitor weather forecasts and avoid driving during periods of heavy rain.

“The soils are already saturated from the rains we had in January and February and now we’re going to put more water on top of that,” said Brian Garcia, a meteorologist with the National Weather Service, in a statement released by the county. “Soils are already oozing out water so that is going to result in flooding and/or mud slides.”

On Wednesday, the county activated its Emergency Operations Center to coordinate local response to a storm expected to bring sustained winds of 25 to 35 mph with gusts in the higher elevations possibly reaching 70 mph, the statement said.

More rain, along with the risk of flooding and slides, is expected through the weekend and into next week, according to the county's statement.

Residents are advised to sign up for SMC Alert, which sends emergency messages to email, cell phones and other devices and landline telephones.

Menlo Park

The city of Menlo Park said in an email Thursday morning that it has filled sandbags available at the Burgess Drive/Alma Street sandbag station and Ivy Plaza at 413 Ivy Drive. Sandbags and loose sand are available at: Burgess Park parking lot at Alma Street and Burgess Drive; Menlo Park Fire Station No. 77 at 1467 Chilco St.; and at a temporary pop-up at the Pope Street island at 222 Laurel Ave.

City crews have taped off and placed no parking signs along portions of Woodland Avenue due to concerns that saturated soils from previous rains and this latest storm will make creek banks unstable and hazardous. "Additional areas along the entire length of the creek banks may pose hazards, so please observe the creek from a safe distance and monitor creek levels online at menlopark.gov/creeklevels," the email said.

Atherton

Atherton police said they received numerous calls from residents needing help to manually open garages and gates during the last power outage. The town is encouraging people to learn how to do it themselves and posted a link to YouTube tutorial on its website. Atherton's storm information page also includes instructions on what to do if a tree falls is blocking a road or falls onto a home.

Sandbags are available at the self-service sandbag station at Holbrook Palmer Park. Information about proper sandbag placement is posted on the town's emergency preparedness resource page.