A pair of warm storms expected to hit Northern California later this week could dump more than 8 inches of rain in the mountains and have North Coast rivers roaring.
But weather forecasters and hydrologists say the first substantial storms of California’s rainy season are unlikely to put much of a dent in the state’s water-supply woes, nor will they bring much risk of flooding to the parched Sacramento Valley.
On Thursday evening, the first of the two weather systems formed in the tropical Pacific Ocean will hit the West Coast, bringing gusty winds and substantial rain to Washington, Oregon and California, mostly north of San Francisco. A weaker storm is expected to arrive on Saturday.
“It will be rather juicy, I think, when it does arrive to the north part of the state,” said Maury Roos, chief hydrologist with the state Department of Water Resources.
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While between 1 and 3 inches of rain could fall across the Sacramento Valley, with about 1.5 inches in Sacramento, the north state is expected to get a more substantial soaking.
Roos said Shasta Lake, the state’s largest reservoir, could have at least 6 inches of rainfall on its surface during the storms. That could raise the level of the lake – currently at 60 percent full – by as much as half a foot.
There’s little risk of flooding below Shasta and other Central Valley dams, Roos said, since there’s ample room in the reservoirs to capture the rain. The rivers on the North Coast, however, could swell substantially.
Roos said preliminary forecasts estimate the undammed Smith River in Del Norte County, running Tuesday at flows of around 350 cubic feet per second, could move at more than 10,000 CFS during the weekend.
Still, much of the upcoming rain may never reach a reservoir. The reason? Five years of drought have turned mountain watersheds into dry sponges.
“The ground is very dry so we expect much of the precipitation to soak into the ground from the first few storms,” said Shane Hunt, a spokesman for the Bureau of Reclamation, which manages Folsom and Shasta dams, in an email statement to The Sacramento Bee. “We are hopeful that this is the start to a good rain/snow season. We have been reducing releases lately from Shasta and Folsom to conserve storage in the meantime just in case it remains dry.”
Brenda Belongie, a meteorologist with the U.S. Forest Service in Redding, said it remains important for Californians to be mindful of fire danger, though the storms should substantially ease the risk. “(They) ought to soak things down pretty well,” she said.
The storms shouldn’t cause too many problems for people. Because they’re so warm, there’s little concern of snow over the mountain passes, forecasters say.
But street flooding is always possible if storm drains, unused since the spring, become clogged with debris. Gusty winds also might knock down tree limbs in the northern Sacramento Valley.
Jason Clapp, a meteorologist with the National Weather Service in Sacramento, said wind gusts of up to 45 mph are possible in the areas around Redding, Red Bluff and Chico and toward the Sutter Buttes.
After enduring five years of drought, an October storm might seen unusual to Californians, but they’re hardly unheard of, Clapp said. In fact, the most powerful windstorm to hit the West Coast in modern history was in October.
The infamous Columbus Day Storm of 1962 – also known as the Big Blow – brought gusts and heavy rains so powerful they killed dozens of people and caused mudslides and flooding across Northern California, Oregon and Washington. The World Series matchup between the San Francisco Giants and New York Yankees was postponed by several days due to the torrential rain.
Meanwhile, there’s no evidence that a wet October portends a heavy rainy season for California. Forecasters say there’s still nearly as much of a chance that California will experience average precipitation as there is for another dry winter.