What you should know
- A holiday week storm that soaked northern California has penetrated southern California.
- The heaviest rain for SoCal will fall from Thursday evening to Friday.
- Conditions will dry up later on Friday before another storm hits this holiday weekend.
A storm that will bring rain and snow Thursday through Friday has arrived in Southern California.
Mountain snowfall and widespread rain are forecast, with most rainfall falling from late Thursday through Friday. That same system pounded the northern parts of the west coast with rain and snow earlier this week, offering a preview of what is to come.
Here is the storm outlook. This article will be updated.
The rainy timeline for a December storm in Southern California.
Holiday week storm timeline
Rain showers soaked Ventura County overnight, adding up to nearly half an inch in some areas. The storm hit Los Angeles late Thursday morning before spreading to the Orange County and Inland Empire communities later Thursday morning.
“It’s rife at the time,” said NBC4 forecaster Belen De Leon. “It’s best just not to be on the go. Expect travel delays. “
- Thursday morning: rain picks up in LA County
- Thursday afternoon to Friday: widespread rain
- Friday afternoon: rain subsides
- Saturday: Cold storm brings more rain
Showers will be light in the morning, with the heaviest rainfall arriving from Thursday night through Friday morning.
Water vapor images over the Pacific showed an atmospheric flow that develops as moisture currents from an area east of Hawaii. Atmospheric rivers are long clouds of moisture in the skies over the Pacific that have fueled some of the strongest and most damaging storms on the west coast.
Moderate to heavy rain on burn scars from wildfire, such as in the fire areas of Bond, Apple, Silverado and El Dorado, could trigger debris flows Thursday through Friday. These areas are under flood protection.
Here are the effects of a December storm.
Coastal and valley areas will see 1 to 3 inches of rain, and mountain communities will see 2 to more than 5 inches.
The depths of snow will remain over 7,000 feet high with accumulations between 4 and 8 inches.
The gusts will increase on Thursday, reaching 50 to 60 miles per hour in the mountains.
Another system arrives on Christmas Day with showers through Sunday.
“This one will be colder with less rain,” said De Leon. “We’re still a few days away and this storm system could take a different route.”
This graph shows the weather conditions during the weekend in Southern California.
Vacation travel forecast
The window of opportunity quickly closed for motorists when the storm hit the mountains on the west coast of Northern California with rain and heavy snowfall, making travel across the state difficult.
Traveling, especially over high passes, becomes chaos due to the constant and multiple rain, mountain snow and gusty winds. The National Weather Service said that winter storm warnings were in effect in parts of the Sierra Nevada and will last until Sunday.
According to the California Department of Transportation, chain requirements for vehicles were already in place on some sections of the route through the Sierra.
Rainfall was light to moderate in the San Francisco Bay Area and slowly spread down the coast until arriving in Ventura County Wednesday night.
The bigger picture for California’s December weather
In October, the National Oceanic and Atmospheric Administration announced that the Pacific Ocean was showing signs of a new La Nina, the downside of El Nino’s ocean warming, which tends to cause weather changes around the world.
Forecasters said much of California would have a 33% to 50% chance of below average rainfall, while only the extreme northern plain of the state had an equal chance of above or below average rainfall.
US drought monitor
The California Drought Monitor map for December 21, 2021.
But the storm trail has moved further south than is common during La Ninas. After a series of storms in mid-December, California’s total snow to water equivalent – a measure of how much water is in the snowpack – jumped from 19% of normal on December 10th to 76% of normal on December 17th latest US Seasonal Drought Outlook.
While the current wet trend is positive, it’s too early to know if it will last through January and February. Snow cover usually doesn’t peak until April and last spring there was minimal runoff as much of the water was taken up by the arid, arid landscape.