Heaviest rain, wind expected between 4 a.m. and 10 a.m.

A powerful storm expected to batter the North Coast overnight and Thursday bore down on the region Wednesday night, turning roadways slick and sending many residents scrambling to prepare for flooding, as well as power and travel disruptions.

Rain was falling everywhere by the time the Wednesday night commute was underway, setting the stage for a series of minor collisions, and later prompting reports of surface flooding on scattered low-lying roadways in Penngrove, Sonoma and St. Helena.

A fallen tree was blocking one lane of Highway 128 near Chalk Hill Road in the Alexander Valley late Wednesday night as the rain steadily grew worse.

By 9 p.m., 8-hour totals for some areas of west Sonoma County were well above an inch, the National Weather Service said.

But, like the adage says, the storm’s leading edge arrived with all the brutality of a lamb, though gusting winds and profuse rainfall were expected by sunup to deliver a pummeling worthy of an angry lion.

Campus closures were announced Wednesday for more than a dozen schools in the western part of Sonoma and southwest Mendocino County in anticipation of hazardous road conditions, falling trees and power failures.

Sonoma County’s largest district, Santa Rosa City Schools, as well as Santa Rosa Junior College and Sonoma State University were scheduled to be in session, though all reserved the right to change plans early today if conditions warranted.

Armstrong Redwood State Natural Reserve and adjoining Austin Creek State Recreation Area were closed to visitors Thursday and, possibly, Friday after two large bay trees toppled over Tuesday, evidence of the weakened condition of the trees after three years of drought, according to the Stewards of the Coast and Redwoods, a nonprofit agency that operates the parks.

Campgrounds at Still Water Cove and Gualala regional parks were closed, as well, given the forecast for high surf and winds gusting to 70 mph on the coast, a Sonoma County spokeswoman said.

A high wind warning and high surf advisory were in effect throughout the North Coast, and a flash flood watch was expected to be upgraded to a flood warning some time Thursday morning in anticipation that copious runoff would raise most rivers beyond flood stage over the ensuing 24 hours.

That included the Russian River, which was predicted to crest in Guerneville on Friday morning more than 26 feet above the 6.3 feet at which it was measured Wednesday afternoon, though that would put it just a few feet above flood stage.

Forecasters upped the ante on the overall rainfall Wednesday, however, projecting a whopping 5-to-7 inches in Santa Rosa and most of Sonoma County, with upwards of 8 inches in the coastal hills, heaviest between 4 a.m. and 10 a.m. Thursday. In the same time-frame, winds were to be at their peak, National Weather Service meteorologist Steve Anderson said.

That’s roughly the same volume of rain that fell over five days last week in the Marin County community of Kentfield, the wettest spot in the greater Bay Area during the last series of storms, Anderson said.

“Just to compare, we’re expecting about that same amount of rainfall in 12 hours,” Anderson said.

“You put that amount of rain coming down that fast, and the rain’s not going to be able to get out of its own way,” he said. “Boom: flash-flooding everywhere and the creeks, of course, rising up, causing problems, flooding the roadways there.”

Emergency personnel in Petaluma expected that would mean some flooding on the north end of town. “We’re going to be monitoring things really closely through the night,” Petaluma Fire Battalion Chief Jeff Holden said.

The Russian River was expected to reach flood stage in Hopland around 9 a.m. Thursday, cresting about 3½ feet above flood stage at 4 p.m. It was to reach flood stage in Guerneville at 5 a.m. Friday and crest at 1 p.m., less than 3 feet above flood level, causing minor roadway flooding, according to the National Oceanic and Atmospheric Administration’s California-Nevada River Forecast Center.

In southwest Mendocino County, hydrologists forecast a rise on the Navarro River along Highway 128 fast enough to put it at flood stage by 8 a.m. Thursday and raising it about 10 feet by the time it crested at 5 p.m.

The Napa River also was expected to rise, cresting in St. Helena at 5 p.m. Thursday just a few inches above flood stage. The river was not expected to reach flood stage in Napa, the river forecast center said.

Local officials said residents had snapped up thousands of sandbags to help protect their homes and properties. Friedman’s Home Improvement in Ukiah ran out at one point, and had to restock after giving away about 6,000, store personnel said.

In Novato, the city exhausted its supply of 12,000 over a mere 36 hours.

A mound of sand left near the Russian River fire house in Guerneville for use by local residents had to be replenished by the county, as well, fire personnel said.

Along north Sonoma Coast, Timber Cove Fire Chief Dennis Meredith expected he and his volunteers would be running to calls during the night, ahead of most of the county.

“We expect to get it first ... during the night,” Meredith said. “We’ll probably have the biggest winds out in this area.”

With forecasts predicting gusts between 60-and-70 mph on the coasts and ridgetops, the regions coastal mountains are bound to be ripping from the wind, he said.

“It’s not unlike a hurricane, with winds strongest right off the ocean,” Meredith said.

He said the focus of local crews would be keeping down trees from blocking Highway 1. “It’s one of the only routes from the north,” he said.

An effort to move as many homeless residents under cover as possible included the addition of about 100 shelter beds, between shelters operated out of the veterans’ memorial buildings in Santa Rosa, Petaluma and Guerneville, a Sonoma County spokeswoman said. l beds.

Staff Writers Randi Rossmann, Jamie Hansen and Glenda Anderson contributed to this report. You can reach Staff Writer Mary Callahan at 521-5249 or mary.callahan@pressdemocrat.com. On Twitter @MaryCallahanB.