California faces flood risk, burying mountain snow as atmospheric river returns
By Kristina Pydynowski, AccuWeather senior meteorologist
March 06, 2019, 9:54:27 AM EST
As a storm taps into the atmospheric river, the risk for flooding and heavy mountain snow will continue across parts of California into Wednesday.
Rain spread over the state on Tuesday, with the steadiest and heaviest rain arriving Tuesday night. Additional bouts of heavy rain will continue into Wednesday night.
While most of California (outside of the mountains) can receive some rain from this storm, the heaviest rain will target only some areas as opposed to being fairly uniform across the state.
The bands of heavy rain will be more progressive on Wednesday, when compared to Tuesday. That will result in inconsistent rain totals.
"For a time on Wednesday, heavy rain will focus on the Los Angeles basin to the lower slopes of the southern Sierra Nevada," according to AccuWeather Senior Meteorologist Alex Sosnowski.
"A secondary band of heavy rain will extend from near and just south of San Francisco to Sacramento and the lower slopes of the northern Sierra Nevada," Sosnowski said.
"With this rain hitting heavily populated areas of Los Angeles, Sacramento and San Francisco, the risk of flash and urban flooding will be significantly higher than it has been with this storm so far," Sosnowski added.
The drenching rainfall will also reach into rural portions of the San Joaquin and Sacramento valleys.
The atmospheric river caused one band of heavier rain to set up in areas south of San Francisco and just north of Los Angeles Tuesday night, while a separate area of heavy rain targeted areas north of San Francisco.
"With the ground already saturated and 1-3 inches of rain expected, flooding will be an issue," according to AccuWeather Meteorologist Maggie Samuhel.
There can be an AccuWeather Local StormMax™ of 6 inches along the south- and southwest-facing slopes of the mountains. Similar rainfall totals can be expected in Northern California.
"Locally heavy rain and flash flooding will also extend across parts of the California deserts, including Death Valley, as well as southern Nevada, including Las Vegas," Sosnowski said.
In addition to flooding, mudslides are a concern. Residents in areas prone to both of these hazards and near burn-scar areas should remain extremely vigilant and heed all evacuation orders by local officials. Some road closures are also possible.
Mudslides and flash flooding can occur anywhere in the region due to the excessive amount of rain that has occurred in recent weeks.
Even in the absence of the above dangers, downpours can reduce visibility for motorists and heighten the risk of vehicles hydroplaning when traveling at highway speeds.
While no snow is expected, the heavy rain can still make for a slow drive from Los Angeles to Bakersfield along Interstate 5 and through the Grapevine.
The combination of snow and gusty winds is expected to once again bring difficult travel and likely restrictions to I-80’s Donner Summit and other roads through the Sierra.
A general 1-3 feet of snow is forecast over the Sierra Nevada with up to 4 feet in some locales over the high country.
There can also be snow and slippery travel at times along the highest points of I-5 near Mount Shasta in Northern California.
Between the bands of heavier rain and mountain snow, it is possible that rain remains on the lighter side and is more of a nuisance to travelers and those with outdoor plans in a part of central California.
Download the free AccuWeather app to know how much rain is expected in your community.
Isolated thunderstorms also rumbling across Northern and Central California cannot be ruled out with this storm.
As the storm presses into the Rockies, a cool and unsettled weather pattern is expected to follow late in the week.
Periods of snow can continue to stream over the Sierra, further impacting travelers. As snow levels lower, it is possible for snow and slippery travel to return to the Grapevine.
Rain showers may dampen the lower elevations in other parts of the state.
“Looking beyond this week, chilly and unsettled weather can remain the theme in California and most of the West for the middle of March,” according to AccuWeather Senior Meteorologist Brett Anderson.
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