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Rain unlikely to reach drought-starved reservoirs that supply Sonoma County

A series of cold fronts expected to hit the North Bay beginning late Tuesday night could drop 6-to-8 inches of precipitation in the wettest mountain areas through early next week — enough to bring an end to the fire season, forecasters said.

But as rich in water as the rain makes us feel, it doesn’t mean the drought is over. Though welcomed and beneficial, much more precipitation is needed to make even a dent in what’s needed to restore supplies, forecasters and water managers say.

The ground is so parched after two years of critically low rainfall, most of the rain will just be absorbed, leaving little, if any, to accumulate as runoff and feed into streams, rivers and reservoirs, Sonoma Water engineer Don Seymour said.

Nor is a flash of wet weather now a sign that a normal winter season lies ahead, said Brian Garcia, warning coordination meteorologist with the National Weather Service in Monterey. The opposite is still likely.

The bottom line is people need to continue conserving water as if it’s in short supply because it is, in fact, scarce.

“We welcome it,” Sonoma Water Assistant General Manager Brad Sherwood said of the rain, “but we welcome it with a cautionary note, as well — that irrigation systems should be all off right now, that people should still be conserving, please, so the little bit of water we are going to get with these systems we can keep in the reservoir, we can keep in the ground.”

California Gov. Gavin Newsom, meanwhile, declared a statewide drought on Tuesday, with a proclamation that added the last eight counties to the list of 50 that had already been under a state of drought emergency. Sonoma and Mendocino counties were the first on that list in April.

The final eight counties added to the emergency declaration were Imperial, Los Angeles, Orange, Riverside, San Bernardino, San Diego, San Francisco and Ventura. Newsom also reiterated his call for everyone to voluntarily reduce water use by 15% while authorizing the imposition of rules designed to prevent waste of water, such as hosing down sidewalks or driveways.

The first two storm systems coming through the region Tuesday into Wednesday and again Thursday through Friday should arrive at a good pace to allow the thirsty ground to soak it up, Garcia said, raising fuel moisture levels and reducing fire risks.

Forecasters are expecting 2 to 3 inches in most parts of the region by Friday, with up to 3 inches in the coastal mountains and even 4 in the wettest areas, the National Weather Service said.

After a reprieve on Saturday, Sunday is predicted to usher in an atmospheric river — the first one since January — a dense, moisture laden stream of water that could drop an additional 3 to 5 inches of rain in some of the wettest areas, Garcia said.

The atmospheric river was originally trained on Sonoma County and might have brought even more rain to the area, he said. But it but appeared Tuesday to be likely to be centered further south, meaning heavier rainfall would be hitting San Mateo County instead.

Still, if the ground is wet enough by Sunday and the rain comes in fast enough, there could be some runoff formed by the time the storm passes, Garcia said.

Seymour suggested something closer to the 7- to 10-inch range might be needed to saturate the soil enough to produce runoff for the region’s reservoirs, and then two or three times that much, about 25 inches, would be necessary before the end of the year to “bust this drought.”

But right now, dry weather is forecast for most of next week as La Niña conditions intensify along the West Coast, making particularly dry conditions likely in southern areas, wet conditions likely in the north, and leaving Sonoma County in a somewhat questionable, “wobbly” situation right in between.

So far, the storm hose appears aimed to the north, Garcia said.

He recalled the arrival of the season’s first atmospheric river in October 2016, which “went on to be just an absolute record-breaking winter and took us out of the drought we’d been in for 4½ years prior to that.”

“I don’t see that happening,” Garcia said.

Sherwood said he was choosing to be optimistic about the rest of the winter.

“This is a great start. The storm door is open. The parade of storms has begun, and we’re going to be hopeful that the parade doesn’t end,” he said.

You can reach Staff Writer Mary Callahan at 707-521-5249 or mary.callahan@pressdemocrat.com. On Twitter @MaryCallahanB.

Mary Callahan

Environment and Climate Change, The Press Democrat

I am in awe of the breathtaking nature here in Sonoma County and am so grateful to live in this spectacular region we call home. I am amazed, too, by the expertise in our community and by the commitment to protecting the land, its waterways, its wildlife and its residents. My goal is to improve understanding of the issues, to find hope and to help all of us navigate the future of our environment. 

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