Sonoma County to get 5 to 7 inches of rain, flooding in areas

A wet, one-two punch from Mother Nature starting Friday is expected to pump the season’s rainfall total up to normal and boost the water supply in drought-starved reservoirs, officials said Wednesday.

But the two storm systems, which could drop 5 to 7 inches of rain on Sonoma County and the rest of the North Bay through Wednesday, won’t break the three-year drought nor do they foretell a wet winter, officials said.

The water year that began on Oct. 1 got off to an “abysmal start” in the Bay Area despite an inch or two of rain in the past week, the U.S. Drought Monitor said Wednesday. More than half of California - including Sonoma, Mendocino, Lake and Napa counties - remained in the area classified as “exceptional drought,” the highest level of drought.

Nearly 80 percent of the state remained in extreme and exceptional drought, the top two levels.

Rainfall to date in the Bay Area was at 20 to 50 percent of normal, and the “dry, mostly mild start to winter” has produced snowpack in the Sierra Nevada that is “well short of normal,” the drought report said.

But the season’s first major wet spell, with periods of “heavy and extended precipitation” in the Bay Area beginning Friday, could bring rainfall back to normal, National Weather Service meteorologist Steve Anderson said.

On Wednesday, Santa Rosa had recorded 2.2 inches of rain since July 1, ahead of the 1.6-inch total for the same time last year, he said. A little over 4 inches of rain would push the seasonal total up to the city’s 6.26-inch average for this time of year.

“It’s doable,” Anderson said. “Above normal would be even better.”

A hazardous weather outlook issued by the Weather Service on Wednesday warned of “difficult driving conditions” over the weekend and the “possibility of downed trees and power lines” on Monday. Flooding in low-?lying areas of Sonoma County was also expected.

Officials at the Sonoma County Water Agency were “giddy” at the prospect of the rainfall saturating the ground and leading to “some fairly decent runoff” into the region’s waterways and reservoirs, said Brad Sherwood, an agency spokesman.

“We’re very excited,” he said, noting that the runoff from up to 7 inches of rain would be “more than we’ve seen in the last two years,” since a wet spell in December 2012.

Anderson said the first storm, expected to start Friday afternoon or evening and continue through the weekend, would saturate Bay Area soils, setting the stage for runoff during the second storm, expected to start Monday or Tuesday and last for two days.

“The sponge will be saturated at that point so everything that follows will just run off,” he said.

Lake Sonoma near Healdsburg held 56 percent of water supply capacity as of Tuesday, while smaller Lake Mendocino near Ukiah had 41 percent of capacity. Rainfall so far this season had made little to no difference in reservoir levels, Sherwood said.

Water from the two reservoirs serves 600,000 customers in Sonoma and Marin counties.

The hazardous weather outlook noted that the second storm, due to arrive early next week, would be a “more potent system,” with rain and gusty winds.

Urban and low-lying areas in Sonoma County that could experience flooding include the lower Laguna de Santa Rosa area, lower Sonoma Valley near Schellville, Valley Ford and Bloomfield along the Estero Americano, and Two Rock near Stemple Creek, the Weather Service said.

Some small creeks may “reach or slightly exceed flood stage,” the agency said.

The Russian River is expected to reach just 1.5 feet at Healdsburg on Monday, leaving it far below flood stage of 23 feet.

Rain in Northern California through Wednesday was sufficient to sprout grass in pastures and “begin the process of aiding reservoirs,” the Drought Monitor said. But it fell “well short” of bringing relief from the three-year drought, the report said.

“We are still in a drought, that goes without saying,” Sherwood said. “We still have a lot of rain to catch up on.”

Anderson, the Weather Service forecaster, said it would be “a stretch to say” the upcoming storms signal a wet winter.

You can reach Staff Writer Guy Kovner at 521-5457 or guy.kovner@pressdemocrat.com. On Twitter @guykovner.