Atmospheric rivers bring wet weather to San Francisco area and West Coast - The Washington Post

Weather alerts — for dense rainfall successful the lowlands, and snowfall and upwind successful the mountains — broad astir of cardinal and Northern California. Coastal and cardinal Oregon and Washington are mostly nether flood watches and precocious upwind warnings, with wintertime tempest warnings successful the Cascades and Columbia River Basin.

Atmospheric rivers are ranked connected a 1-through-5 standard based connected however overmuch moisture they transport from the tropics to the mid-latitudes. The Center for Western Weather and Water Extremes has ranked the ongoing atmospheric stream lawsuit arsenic a Level 4 retired of 5 — that corresponds to “extreme” moisture transport.

The atmospheric stream could transportation much than 220 cardinal pounds of h2o done the skies implicit the Pacific Coast each 2nd — providing copious substance for downpours.

“[A] beardown tempest [is] presently moving crossed the region,” the National Weather Service successful Sacramento wrote successful their online forecast discussion. “A weaker bid of systems, but longer duration, moves successful opening Wednesday nighttime and continuing into the weekend.”

At present, a lingua of dense moisture stretches from cardinal California, conscionable southbound of the Bay Area, to astir 1,000 miles northbound of Hawaii. The halfway of this moisture plume is astir 200 to 300 miles wide and is aimed owed eastward.

That road of moisture is being entrained and tugged eastbound by a bowling shot of counterclockwise-spinning debased unit moving ashore successful the Pacific Northwest. Some of the moisture is being swirled into that low-pressure system, and with frigid aerial aloft it is contributing to rainfall successful the lowlands and snowfall successful the higher elevations.

Washington and Oregon

Seattle and surrounding areas nether a flood ticker until Wednesday morning. Roughly an inch of rainfall has travel down truthful far, and different 4th to half-inch is astir apt connected the way. That’s added atop the 3.09 inches that fell betwixt Christmas Eve and Dec. 26.

“Ground conditions are already saturated from erstwhile storms. The further rainfall connected Tuesday could propulsion immoderate rivers to flood signifier aboriginal Tuesday into Wednesday morning,” the Weather Service said.

Even arsenic the rainfall tapers down implicit the adjacent 24 hours, the winds volition howl. They’ll ramp up markedly retired of the southwest during Tuesday afternoon, peaking astir evening earlier subsiding during the 2nd fractional of the overnight. The National Weather Service is informing that gusts up to 55 mph are possible.

Those beardown winds volition heap h2o up against the coastline, prompting a coastal flood advisory for Seattle and overmuch of greater northwest Washington.

“Flooding of lots, parks, and roads with lone isolated roadworthy closures [is] expected,” wrote the Weather Service.

In the Cascades, up to 60 inches of snowfall are probable successful the highest, albeit unpopulated, summits. Winter upwind advisories are successful effect for the mountains, though, wherever snowfall levels could driblet down to 2,500 feet. Communities supra that enactment could spot a premix of snowfall and ice, with immoderate apt to prime up arsenic overmuch arsenic a ft of snowfall accumulation.

Farther to the southbound successful Oregon, Salem, Eugene and the Willamette Valley are each nether high-wind warnings. Beaches, headlands and different exposed locations could gust implicit 70 mph, though astir inland areas volition spot speeds of 55 to 60 mph.

California

The Golden State is seeing its ain inclement weather. Flood advisories span from Santa Rosa done the Bay Area and southbound to the Salinas Valley. San Francisco was sitting astatine a 24-hour rainfall full of 1.78 inches arsenic of 9 a.m. section time, and different half-inch to an inch could beryllium connected the way. A akin lawsuit connected Dec. 10-11 dropped 1.84 inches successful San Francisco.

Wind advisories and high-wind warnings are successful effect crossed the cardinal and bluish San Joaquin Valley, but the worst conditions, with gusts topping 100 mph, volition beryllium felt successful the Sierra Nevadas. That’s wherever a wide 3 to 4 feet of snowfall is falling. Winter tempest warnings screen the mountains, with snowfall rates of 4 inches per hr likely.

Thus far, Interstate 80 implicit Donner Summit has been successful bully capable information that concatenation power — erstwhile road conditions necessitate that vehicles person chains — has been lifted, but snowfall levels whitethorn driblet beneath 6,000 feet during the evening hours. That volition enactment the walk astatine hazard of dense snowfall erstwhile again.

The effects of the atmospheric stream volition taper disconnected overnight arsenic the atmospheric stream drifts southbound and thins.

Some betterment is apt Wednesday and Thursday crossed the West, but determination are signs of different atmospheric stream lawsuit connected the way. The instigating low-pressure system, disposable arsenic a swirl connected h2o vapor imagery, is presently sliding eastbound to the southbound of the Alaskan Aleutians, and volition tug ashore different ribbon of moisture arsenic we caput into the weekend.