New atmospheric river slamming California with heavy rain, mountain snow
The barrage of storms continues for the Golden State, as many residents are still dealing with flooding from the deadly storm that moved through late last week.
The latest atmospheric river to strike California caused major power outages around the Bay Area on March 14 as snow kept pummeling high elevations.
Californians were bracing for another potent storm system from the Pacific Ocean that AccuWeather meteorologists say will lead to widespread travel disruptions, aggravate ongoing flooding problems and add to the record amount of snow over the Sierra Nevada.
The dangerous storm will create a plume of moisture, called an atmospheric river, that will spray heavy rain like a giant firehose from north to south across the storm-weary state into Tuesday night, but problems associated with runoff and heavy high country snow will persist through at least Wednesday.
At least two deaths were reported from the storm this past Friday, which also led to a number of evacuations and caused the National Weather Service to issue two rare flash flood emergencies in Central California.
"This will be another significant atmospheric river event for California and will lead to major flooding problems in parts of the state," AccuWeather Senior Meteorologist Ken Clark said.
The storm will deposit a general 1-4 inches of rain across much of the state, with the exception of the deserts in the southeast, forecasters say. Along the west-facing lower and intermediate slopes of the Sierra Nevada, a general 4-8 inches of rain is expected, and an AccuWeather Local StormMax™ of 12 inches is possible.
"The heaviest rain and worst travel conditions in the San Francisco Bay Area began Monday night and persisted into Tuesday morning," AccuWeather Senior Meteorologist Heather Zehr said. The Tuesday morning commute around San Francisco was nasty with gusty winds that created a driving rain.
As expected, gusts between 40 and 60 mph started around San Francisco Tuesday morning and persisted for several hours, even after the heaviest rain moved away, leading to power outages around the Bay Area as trees toppled over in the saturated soil. San Francisco International Airport even reported extreme gusts to 73 mph around noon Tuesday PDT. Many in the region remained in the dark several hours later and as of 3 a.m. Wednesday PDT, the number of utility customers without power in California was just under 200,000, according to PowerOutage.us.
"As for the Los Angeles area, the worst conditions in terms of rain and flooding will be from Tuesday afternoon through Tuesday night," Zehr said. "Travel from the Tuesday evening rush hour through the overnight hours over much of coastal Southern California will be plain old rotten."
In terms of this atmospheric river's impact on Southern California, when compared to the one from late last week, this storm will be worse due to heavier rain that is forecast to fall and the scope of flooding and mudslides that could be unleashed.
Since the ground is saturated from the frequent winter storms that have bombarded much of California, it will not take as much rain to cause problems. Most of this storm's rain will run off into area streets, streams and major rivers.
With a growing number of reservoirs now releasing water, rather than retaining from drought recovery, water through some streams will flow with a force that has not been seen for a few years. Moderate to major flooding is possible along some of the bigger rivers as the new batch of rain pours down and works through the hillsides and into the valleys and streams over the next several days. The additional rain may lead to new evacuations, including one issued in the Southern California city of Grover Beach on Monday and another issued in Shasta, California, on Tuesday due to heavy flooding.
Some levees may again be stressed, resulting in damage or failure that will further escalate flooding risk. After a levee breach in the Monterey County community of Pajaro last week, over 239 rescues were made by first-responders.
Motorists should be prepared for high water that may block their route. In some cases, roads and bridges could be washed away, while mountainsides become unstable and give way.
"Like the storm from last week, snow levels will be quite high with this storm and will generally fluctuate between 7,000 and 8,000 feet during the first part of the storm," Zehr said.
This means that rain will fall on top of a deep snow cover that is already loaded with moisture. While last week's storm wiped out a great deal of snow over elevations below 5,000 feet, an extensive amount of snow remains on the ground in some areas, especially from 5,000 to 7,500 feet. Additional rain will melt some of that snow cover, but it will also add weight which may be too much for some roofs to handle. In some cases, roof damage or collapse may occur.
As slightly colder air rotates in on the backside of the storm, a change from rain or a wintry mix to snow will occur over Donner Pass, along Interstate 80, on Tuesday night. Snowfall amounts ranging from 1-3 feet could slow or shut down travel into Wednesday.
The rain and heavy wet snow could significantly increase the avalanche threat in steep terrain.
Over the high country, where temperatures will remain below the freezing mark throughout the storm, a couple of yards of snow will pile onto the tremendous snowpack that has been in the making since late December.
In terms of water content locked up in the snow, this winter has now set a record, surpassing that of the winter of 1982-83 for the southern Sierra Nevada and is only second to that same winter for the central and northern Sierra Nevada, according to the California Department of Water Resources.
Source: California Department of Water Resources
There is now about 2.5 times the historical average of water locked up in the snow cover in the southern Sierra, more than double the average in the central Sierra and 1.6 times the average across the north.
The amount of water locked up in the massive amount of snow on the ground will be released during the spring and early summer and should continue to alleviate leftover drought conditions but also contribute to ongoing flooding.
Additional storms will affect California as March progresses, with the next potential significant system forecast to roll in from the Pacific early next week.
AccuWeather meteorologists will continue to provide updates on the current storm and new information on the storms that follow into the spring.
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