At­mo­spheric river to bring storm, flash flood warn­ings

Storm will dump snow across cen­tral Sierra and rain­fall to wine coun­try burn scars.

Los Angeles Times - - CITY & STATE - By Joseph Serna joseph.serna@la­times.com Twit­ter: @JosephSerna

The first at­mo­spheric river-fueled storm of the sea­son is ex­pected to make land­fall in Cal­i­for­nia on Wed­nes­day af­ter­noon, when it will dump inches of rain in the Bay Area, dis­gorge up to a foot of snow over the Sierra Ne­vada and prob­a­bly trig­ger flash floods in fire-scorched wine coun­try.

The Na­tional Weather Ser­vice is­sued a flash flood warn­ing from 4 p.m. Wed­nes­day to 3 a.m. Thurs­day for ar­eas of Sonoma and Napa counties scorched by a mul­ti­ple wild­fires in Oc­to­ber.

Rain could fall at a rate of about a half-inch an hour — heavy enough to trig­ger flash floods, Na­tional Weather Ser­vice me­te­o­rol­o­gist Anna Sch­nei­der said.

Af­fected ar­eas in­clude the re­cent At­las, Tubbs, Nuns and Pocket burn scars, as well as the Foun­tain­grove neigh­bor­hood in north­east Santa Rosa, the weather ser­vice said. Ef­fects in­clude de­bris flow, mud­slides and flash flood­ing.

Fore­casts say the storm could drop 3 to 5 inches of rain in the coastal moun­tains and less in the Cen­tral Val­ley, while also bring­ing 50-mph wind gusts. The storm will move south and is fore­cast to drop up to 11 inches of snow across much of the cen­tral Sierra, with some ar­eas see­ing up to 34 inches, the Na­tional Weather Ser­vice said.

As the storm ap­proached Tues­day, Cal­trans an­nounced it had closed two state high­ways through the north­ern Sierra and lim­ited driv­ing on an­other road to chains-only.

Still, Sch­nei­der said, this up­com­ing at­mo­spheric river is “weak com­pared to how bad they could be.”

Cal­i­for­nia’s drought-bust­ing 2016-17 win­ter was fueled by more than 30 at­mo­spheric river events — Pa­cific-based storms that are hun­dreds of miles wide and can hold as much wa­ter as the mouth of the Mis­sis­sippi. Those storms re­plen­ished dwin­dling sur­face-level wa­ter re­serves and packed record amounts of snow onto the Sierra Ne­vada.

Though this wa­ter year — which be­gan Oct. 1 — isn’t off to as fast a start as the last, it’s still not too shabby, state cli­ma­tol­o­gist Michael An­der­son said.

“The rainy sea­son is back,” An­der­son said.

The gov­ern­ment’s fourth Climate Sci­ence Spe­cial Re­port, re­leased Nov. 3, said Cal­i­for­nia will prob­a­bly see more in­tense at­mo­spheric rivers with greater fre­quency in the fu­ture be­cause of climate change.

The storm should hit the en­tire north­ern half of the state by Fri­day and pack enough mois­ture to wet the ground af­ter the hottest sum­mer in recorded his­tory, An­der­son said. Early sea­sonal rain helps cre­ate a foun­da­tion for the win­ter snow­pack to pile onto — a pre­cious liq­uid re­source for farm­ers when it melts in the spring and sum­mer.

The edges of the sys­tem might bring light rain to Ven­tura and north­ern Los An­ge­les counties Thurs­day.

Brian van der Brug Los An­ge­les Times

RAIN EX­PECTED in North­ern Cal­i­for­nia on Wed­nes­day could trig­ger de­bris flows, mud­slides and flash flood­ing in the ar­eas burned in last month’s wild­fires.

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