A drenching storm that dumped more than half a foot of rain on the wettest areas of Sonoma County early Friday caused minor flooding around the region and left emergency personnel worriedly waiting to see what would come next.
A storm on the horizon for late Saturday and Sunday morning promised significant new rainfall and — with the ground fully saturated from earlier precipitation — predicted trouble, authorities said.
"Sunday is the day we're worrying about," said Sonoma County Emergency Services Manager Chris Helgren. "...That's why we're making the recommendation that, unless you have to be out, don't."
The Russian River was forecast to overflow in Hopland on Sunday morning, though only by 2 or 3 feet — still enough to close Highway 175, the CHP and National Weather Service said.
A flood watch also was issued for Guerneville, though the river was expected to crest a foot below flood stage at its predicted peak on Monday morning, the weather service and state Department of Water Resources said.
The Navarro River topped its banks Friday, closing Highway 128 near the Mendocino Coast, and was expected to flood again before the weekend is through, the CHP and weather service said.
Farther south in Mendocino County, a flood on the Garcia River closed Highway 1 on Friday, the CHP said.
"Now that the ground's saturated, I think the creeks are a little quicker to come up, and we're also starting to see little mudslides along the road here," said Rancho Adobe Fire Capt. Herb Wandel in Penngrove. "That will also increase."
With yet another, weaker storm forecast to arrive Tuesday, emergency officials were just grateful for lulls between systems going through the area, permitting prodigious rainfall from each to recede somewhat before the next onslaught.
"That's sort of our saving grace at this point is those breaks between," said Pam Jeane, assistant general manager at the Sonoma County Water Agency.
But runoff from previous rains was still flowing into local waterways, raising local creeks across roadways. The ground has absorbed so much moisture it not only can't take anymore, it has loosened its grip on trees, power poles and fence posts. A tree crushed a motor home outside of a Sebastopol residence and there were reports of downed power lines and loose cattle, fire personnel said.
Falling trees and branches brought down power lines around the county. At one point Friday afternoon, close to 850 customers were without power, a PG&E spokeswoman said.
Several hundred others had been without lights at some point in the previous 24 hours but had their power restored, spokeswoman Brittany McKannay said.
Wind speeds will be one key to how the area fares this weekend, especially so early in the season, when leaves on the trees work like sails and amplify the force of gusting winds, Helgren said.
National Weather Service meteorologist Diana Henderson said the next storm was forecast to bring sustained winds of about 10-15 mph, gusting to about 20 mph with sustained coastal winds of about 25 mph. But it was nothing close the gusts near 50 that hit the area during a storm Wednesday morning.
The next storm could bring "maybe a couple of 30s here and there, but nothing like we had," she said.
Authorities were taking nothing for granted, however.
"On Sunday, our biggest concern is low-lying houses in the Hopland area, and then low-lying houses on the Navarro," said Mendocino County Sheriff's Sgt. Shannon Barney, the county's emergency services coordinator.
The next storm, expected to hit after 8 p.m. Saturday, was expected to drop 3-6 inches of rain in Sonoma County, the weather service said.
It could leave 7-10 inches in some areas of Mendocino County, the weather service said.
That's close to what pelted the North Coast on Friday morning, raising creeks around the area, flooding low-lying intersections, inundating sewer lines and closing two rural schools.
Rainfall totals from noon Thursday to noon Friday included a whopping 8 inches in the hillside community of Venado outside Healdsburg, 5.57 inches in Monte Rio, 3.52 inches at the Charles M. Schulz-Sonoma County Airport, 3.74 inches in Valley Ford and 2.4 inches in Petaluma, the weather service said.
Early morning creek and surface flooding closed numerous low-lying intersections, trapping more than a dozen motorists who tried to venture through.
At one point, as many as eight vehicles were stranded in flood waters at Highways 12 and 121 near Schellville, the CHP said.
Motorists also were trapped at Rohnert Park Expressway and Stony Point Road near Rohnert Park, Slusser Road at River Road near Forestville, and Freestone-Valley Ford Road near Highway 1.
Excessive rain also inundated sewer lines on Highway 12 near Agua Caliente, spilling untreated but highly diluted sewage onto the street and into a nearby creek at 100 gallons a minute, the Sonoma County Water Agency said.
Spokesman Brad Sherwood said the sewage was highly diluted. He said wastewater flows into the Sonoma Valley treatment pond went from 2.7 million gallons per day Thursday night to 10 million gallons per day on Friday because of the influx of rainwater.
Crews were at the scene by about 2 a.m Friday and cut the overflow by more than a third by early afternoon.
Elsewhere, high tide shortly before 2 p.m. raised the Petaluma River, a tidal slough, above flood stage, causing water to back up into low-lying areas in northern Petaluma around the junction of Old Redwood Highway, Petaluma Boulevard North, Stony Point Road and Industrial Drive.
Parking lots at two buildings in the industrial park were flooded. Run-off also covered an area best known for Groverman's Pumpkin Patch and Corn Maze, Petaluma Fire Battalion Chief Phil Sutsos said.
A flash flood watch remains in effect through Monday morning, and Helgren said more localized flooding can be expected in both rural and urban areas of Sonoma County.
Authorities said residents need to be prepared to change their driving habits and avoid flooded areas, perhaps lose power, and stay alert to changing conditions.
"We're not quite out of the woods yet," Henderson said.
(You can reach Staff Writer Mary Callahan at 521-5249 or mary.callahan@pressdemocrat.com.)
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