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Environment

Napa County hit by a drought-denter, but not drought buster

Heavy rains over several days caused the Napa River in Calistoga to flow in torrents, as seen Oct. 24.

Napa County after a drought-denting — but not destroying — deluge had a section of Silverado Trail closed, wildfire dangers tamped down and reservoirs starting to see runoff.

And all of this happened in a newly born rain season that hasn’t even made it to Halloween. A few storms last week proved to be a mere warmup to virtually 24 hours of non-stop, pounding rain from Saturday night into Sunday night.

Can you bust a two-year drought of almost historic proportions in only a few days?

“Well, no, definitely not,” said Mike Pechner of Fairfield-based Golden West Meteorology.

We don’t yet know the totality of a coming winter with La Nina conditions, Pechner said. La Nina winters are dry 60% of the time. It will take a normal rain year to end the drought.

“No,” National Weather Service meteorologist Brayden Murdock agreed. “It made quite a dent ... we’re in quite a deficit, but this is a big step. Think of it as win, but one step forward after taking three steps back.”

But what a step forward. The start to rain season 2021-22 is stupendous.

Rain totals taken from the local One Rain gauge network as of Monday morning tell the soggy story. The city of Napa corporation yard for October has had 8 inches, St. Helena 14.12 inches, Angwin 14.72 inches and Mount Veeder 16.90 inches.

Napa State Hospital as of 4 p.m. Sunday had 6.78 inches for October and the new rain season. For comparison, it had 10.24 inches during the entire, previous rain season. The average rainfall for an entire season is about 25 inches.

Then there are the 24-hour totals from the atmospheric river rain conditions over the weekend. Pechner said Mount Veeder had 11.74 inches, Angwin 10.6 inches and the Napa corporation yard 7.37 inches.

Whether Napa County set any one-day records remains to be seen. Murdock said the National Weather Service didn’t know as of Monday morning when it was still monitoring the storm in Monterey.

But the National Weather Service reported San Francisco’s 4.02 inches over 24 hours looks to be the fourth wettest day there on record. Downtown Sacramento set a one-day record with 5.44 inches, breaking the previous record set in 1880.

Rain from the weekend’s atmospheric river conditions left a mark on Napa County. County spokesperson Leah Greenbaum on Monday said the country received hundreds of reports of mudslides, downed trees, rock slides and localized flooding.

“It’s going to be a few days to get everything cleaned up,” she said.

For drivers, one event of note was a washout that undermined a section of Silverado Trail between Meadowood Lane and Madrone Knoll Way. Silverado Trail — a major north-south Napa Valley roadway — was closed in both directions as of Monday pending repairs.

“It’s very early in the assessment, but we hope to have the road opened in a week or less,” county Public Works Director Steven Lederer said Monday morning.

Another was the closure Monday morning of Highway 128 at Lake Berryessa between Markley Cove and Monticello Dam, which was closed for several hours before crews could clean up a mudslide. Greenbaum said a report done after the 2020 LNU Lightning Complex Fire identified this as a severe burn area vulnerable to a slide.

Lake Hennessey reservoir, a major city of Napa water source in the mountains east of Rutherford, within a few days rose from 58% full to 66% full. During the 2020-21 rainy season, it actually lost water.

Creeks that barely ran last rainy season over the weekend surged with water, as did the upvalley stretches of Napa River. They went from bone-dry to reborn in the course of a few days.

Hillsides that looked primed to burn a couple of weeks ago as of Monday were soaked. Pechner said the storms put an end to fire season.

“The earliest we’ve seen the end of fire season in, I don’t know how many years,” he said.

Last year, Napa County faced the threat of public safety power shutoffs because of fire danger weather into December.

The weekend's atmospheric river sent Napa River levels near the city of Napa spiking. Levels near Oak Knoll Avenue north of the city of Napa went from about 2.6 feet to more than 21 feet in 14 hours.

Flood control gates on McKinstry Street shut at 9 p.m. Sunday in anticipation that the river might spill into the flood control bypass between the Oxbow district and downtown Napa. Workers scrambled to move portable toilets and other items in the bypass, though they couldn’t remove the Oxbow Riverstage.

As it turned out, the river lapped over the weir, but didn’t surge through the bypass. Rick Thomasser of the county Flood Control and Water Conservation District said a low tide at peak river stage is probably the reason why.

The thought of the bypass flowing in October with the rain season barely begun is something of a stretch. It hasn't happened since the bypass completion in 2015.

Atmospheric rivers usually happen in December through February, Murdock said. The last time one happened locally in October was 2015.

The National Oceanic and Atmospheric Administration describes an atmospheric river as a flowing column of condensed water vapor that produces significant levels of rain and snow. Atmospheric rives are responsible on average for 30% to 50% of normal rainfall on the West Coast.

These atmospheric rivers are about 250 miles to 375 miles wide on average. They are present somewhere on earth at any given time, according to the agency.

Few in Napa County will have any doubt where the location was over this past weekend.

No encore performance is in the immediate forecasts. Napa County might see some rain Tuesday and on the weekend, but as of Monday, the National Weather Service had no drought-busting storms predicted.

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You can reach Barry Eberling at 256-2253 or beberling@napanews.com.

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Napa County Reporter

Barry Eberling covers Napa County government, transportation, the environment and general assignments. He has worked for the Napa Valley Register since fall 2014 and previously worked 27 years for the Daily Republic of Fairfield.

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