Dangerous storm to flood California, threatening lives and property through Christmas
Flash flooding and mudslide risks continue in Northern California and will rise in Southern California through Christmas Day as heavy snow blocks Sierra Nevada roads.
Heavy rain from a powerful atmospheric river caused rockfalls and road issues in Ventura County, California, on Dec. 24. Crews were seen clearing debris as the storm continued to soak the region.
A strengthening storm off the West Coast is bringing another atmospheric river, delivering heavy rain across much of California through Christmas Day, potentially causing life-threatening flooding and mudslides.
Heavy rain will create a significant risk to lives and property in some areas. Feet of snow in the Sierra Nevada may not only close some roads but also leave people stranded.
Multiple inches of rain will continue to fall over a few hours' time across California's mountainsides and urban areas. Those in the coastal regions of Southern California will receive multiple months' worth of rain in a span of one to three days.
"The downtown Los Angeles area is projected to receive 4-8 inches of rain through this week alone, which is two to three times the entire December historical average rainfall of 2.48 inches," AccuWeather Senior Meteorologist Tyler Roys said.
Some of the west- and southwest-facing mountain slopes of the Transverse Ranges in Southern California will receive up to a foot of rain, with an AccuWeather Local StormMax™ of 16 inches, leading to tremendous and rapid runoff.
The heavy rain expected across Northern, Central and Southern California for much of this week could turn small streams into dangerous rivers, send fast-moving water across roads and even wash out some highways. As the ground becomes saturated, the risk of mudslides increases significantly.
"The fast-moving runoff can pick up rocks, mud, ash and debris, quickly turning into a debris flow that can race downhill with little warning, taking out homes, vehicles and roads along the way," AccuWeather Meteorologist Brandon Buckingham said.
Debris flows may be most common in recent wildfire burn scar locations, including the January Palisades and Eaton wildfires.
Downpours will reach the high and low deserts in California and part of the Great Basin in the southwestern United States through Friday.
Heavy snow to create dangerous travel in Sierra Nevada
"Feet of snow will pile up on the Sierra Nevada this week with many of the ridges and peaks in the region picking up 8-12 feet of snow and some places perhaps picking up 15 feet," Rayno said.
Snow will reach lower elevations in the Sierra Nevada this week, potentially dropping to 5,000 feet on Christmas.
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"At Donner Pass, California, along the heavily-traveled Interstate 80, from 2-4 feet of snow is forecast through Christmas Day and into Friday," Roys said.
Some roads, including Interstate 80, may be closed temporarily.
The snow will be a boon for the ski resorts and a future source of water during spring runoff, but with prolonged and heavy snowfall, some people traveling to and from the resorts may become stranded.
Airline delays anticipated
"Air travel through major hubs, including Los Angeles, San Francisco and Sacramento, California, could face delays due to strong winds, reduced visibility and runway flooding," Roys said.
Substantial flight delays and cancellations are possible.
High winds could cut power
Wind gusts are another threat from this storm, which can break tree limbs and lead to power outages.
Some of the strongest wind gusts of 60-80 mph will occur in the Sierra Nevada, the northern and central coasts of California and around Mount Shasta into Thursday evening and night before diminishing. The AccuWeather Local StormMax™ of 130 mph is most likely in the mountains.
With this potent system, some local thunderstorm activity can't be ruled out, with the potential for hail and possibly a couple of tornadoes or waterspouts.
Still damp to end the week
Later in the week, from Friday to Saturday, the storm's intensity will begin to ease, but cold air will remain and moisture will linger.
By the end of the week, snow may fall on the passes in Southern California along I-5 and I-15, resulting in slippery travel.
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