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Climate and Environment

A Massive Winter Storm Hit Southern California — Here's What We Know

A swirling cloud mass is visible over the Atlantic Ocean nearly the U.S. West Coast.
A view of the powerful storm system approaching the U.S. West Coast Wednesday.
Courtesy Cooperative Institute for Research in the Atmosphere)
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A big winter storm pounded Southern California overnight and into Thursday, with a cold front moving through the region faster than expected in the early morning hours. But the worst of the winter storm is over for the remainder of the week.

We should continue to expect showers and wind Thursday, according to the National Weather Service. That's a concern because they could trigger mudflows and create dangerous driving conditions.

The storm left behind flooding of major freeways and a rockslide in Malibu.

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What Else You Should Know

  • Wind gusts reached higher-than forecast speeds overnight — as of 2 a.m. Thursday, peak wind gusts reached as high as 87 mph in L.A. County near Magic Mountain, according to the National Weather service
  • Possible dangers from those high winds include power outages and downed trees
  • As of 4 a.m. Thursday, here are some of the highest two-day rainfall totals so far:
    • Sepulveda Canyon at Mulholland: 3.14 inches
    • Woodland Hills: 2.96 inches
    • Beverly Hills: 1.8 inches
    • Santa Monica: 1.03 inches
    • LAX: 1 inch

About That Rain

Dark cloud and wet streets with palm trees visible in the twilight
Pedestrians on Sunset Avenue in Silver Lake during a small reprieve from the rain on Wednesday, January 4, 2023.
(Samanta Helou Hernandez
/
LAist)

The Pacific storm moving through Los Angeles County brought in light to moderate showers, alongside strong winds. The National Weather Service said they received several reports of downed trees in the region.

Dangerous surf conditions, erosion, and even localized flooding hit some areas of the coast. There was also a risk of power outrages, mud and debris flows in recent burn areas, and rock and debris affecting roads.

Los Angeles County Public Works is keeping close watch on recent burn areas and other trouble spots for flooding. That includes burn areas around Lake Hughes, as well as the San Gabriel and Antelope valleys.

A Yellow Alert is expected to be lifted at 6 a.m. Friday for Duarte residents living near the Fish Fire burn area. Rainfall there came just under half an inch of rain per hour, below the threshold to typically trigger mudslide and debris flows, said Larry Breceda, the city's Public Safety Manager.

"Now we did have pretty consistent and constant rain throughout the night so the soil is pretty saturated, but that's not going to be the major issue. The major issue is going to be saturation on top of rain intensity," he said.

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For now, officials are urging residents to monitor the weather and signs of shifting earth.

Earlier Thursday, a rock slide temporarily closed the westbound lanes of the Pacific Coast Highway in the Malibu area, according to the Sheriff's Department.

But the rain is working in our favor in other ways, according to Public Works' Steven Frasher.

"The rainfall is enabling us to renew our underground aquifers, renewed some of that local water supply. Stormwater accounts for about one-third of L.A. County's water supply," Frasher said.

Eric Boldt, with the National Weather Service, told us that while the rain totals aren't record-setting, Southern California only sees these types of storms every 5-10 years.

"So it is significant, it's definitely going to help generate some water flows, and maybe help get our reservoirs filling again," he said. "That's the good news. And we're also seeing more rain in our future."

Even if the rain has stopped and the sun is pushing through the clouds, Frasher cautioned drivers to slow down and use their headlights. The roads will remain slick for a while.

Helping People Experiencing Homelessness

Seven people experiencing homelessness near the San Fernando Valley's Hansen Dam and Sepulveda Basin were contacted Wednesday by the Los Angeles Homeless Services Authority, which collaborates with law enforcement, the Parks department, and L.A. Fire when flood warnings are issued.

Five of those people, including a couple with five pets, were matched to interim housing, according to a LAHSA spokesperson. The Sepulveda Basin flooded on Thursday.

L.A. Mayor Karen Bass also announced that an unknown number of people living in Venice encampments were recently housed following the declaration of a state of emergency over homelessness.

Flood Watch

Overnight flood watches and warnings are in place through Friday evening.

The NWS says of the risk:

Significant flash flooding is possible anywhere. This includes mud and debris flows in and below recent burn scars. Urban areas should be expect significant flooding of some roads and freeways, with major delays or closures. Excessive runoff will result in flooding of creeks and streams. While the risk of main stem river flooding is low, water flowing through normally dry rivers and washes will threaten homeless encampments.

Road Closures And Conditions

A number of accidents and flooded roads were reported throughout the morning on Thursday.

That included the 710 freeway near the 91, where crews had to use pumps to clear flooded lanes. The northbound I-5 past Lankershim Boulevard was also temporarily blocked due to flooding.

You can always stay up to date on road conditions by checking SigAlert.

A Note To Drivers On Our Roads

  • Check your car
  • Know that middays can be the most dangerous
  • Plan ahead
  • Turn on your headlights
  • Slow down!
  • If you do end up skidding, don't panic
  • Don't drive through standing water
  • Pay attention, duh

We have more detailed guidance: Your Guide To Driving Safely In The Rain In LA (And Really Anywhere).

The Context

Southern California is experiencing an "atmospheric river," which the National Weather Service reports is the third to hit California since Dec. 26.

Gov. Gavin Newsom signed a statewide emergency declaration in anticipation of the storm.

What You Should Know About Atmospheric Rivers

A single atmospheric river can carry more water than the Mississippi River at its mouth and its winds can be dangerous.

A band of blue delineates the path of an atmospheric river with text explaining the science behind them
(Courtesy NOAA)

But these phenomena are also a normal part of West Coast weather, bringing sorely needed rain and adding to the snowpack that's a key source of our state's water.

At the same time, it's the same weather event that triggered the catastrophic Montecito mudslide in early 2018.

NWS' Boldt says you can think of atmospheric rivers just like the name implies: a river in the sky.

"So an atmospheric river is basically the fuel of a storm system over the Pacific Ocean," he said. "It really taps into a lot of water vapor that is streaming over the top of our heads and fueling the storm system as it moves to California."

He says this particular atmospheric river came from Japan.

Here's what the current atmospheric river looked like as it approached us:

You can read more about atmospheric rivers in this 2018 story from our newsroom.

Impact On The Drought

We're still in a drought. As our reporter Jacob Margolis noted, this is normal for our rainy season, and even if we see an average amount of precipitation, higher temperatures from climate change mean everything dries out faster — making drought conditions worse.

Still, the rains have helped improve our drought situation. This is what drought conditions look like as of this week, according to the U.S. Drought Monitor:

A multi-colored map of California shows vast swaths of the state in drought, with red indicating extreme drought across the central valleys, and bands of orange around that.
(Brad Pugh
/
CPC/NOAA)

About OC Canyons

Orange County officials warned residents of canyon areas to be on high alert for potentially dangerous conditions. Officials asked residents to place sandbags around their property and stay off the roads as much as possible in case of mudslides or flash flooding.

Shannon Widor, with OC Public Works, said there were already bulldozers and trucks on canyon roads so that if any mud or debris does cross roadways, it can be cleared as quickly as possible.

"We also have staff going out driving through the canyons and inspecting those areas and keeping an eye on conditions and seeing how rainfall is treating those hillsides," Widor said. "So that way, we can have crews see in real time, see what the conditions are like, and we can take action if needed."

He also encourages canyon residents to register at alertOC.com to receive emergency notifications if there's an evacuation order or flash flood warning.

What's Next

National Weather Service meteorologist Ryan Kittell explained what to expect Thursday night.

"We'll see things tapering down, and by early tomorrow morning, everything should be dry," Kittell said.

Drying roads, that is — not the ground. It's soaked.

Any additional rain will be less than a quarter-inch, Kittell said. Along the coastal areas, dangerous waves are forecasted. Elevated bacteria levels are expected due to rainwater run-off.

Another storm is forecast to arrive in Southern California and deliver our next round of rain by Sunday night, and two other days of rain are expected next week.

How We're Reporting On This

This story has been reported by our newsroom, including contributions by Rebecca Gutierrez, Nate Perez, Gillian Morán Pérez, Mike Roe, Susanne Whatley, and Mariana Dale. We will continue to bring you the latest from the National Weather Service and our own reporting across the Greater Los Angeles area.

What Questions We're Asking

  • What damage did the storm cause?
  • How has the storm affected traffic?
  • When will the rains and wind come to an end?

Learn more

Your Questions Or Ideas

What questions do you have about the weather we're experiencing?
A massive winter storm is hitting Southern California. We're here to answer your questions.
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Corrected January 5, 2023 at 9:20 AM PST
A previous version of this story used the wrong pronoun for meteorologist Ariel Cohen. LAist regrets the error.