what to know
- A storm brings light to moderate rain to Los Angeles overnight and most of Friday.
- Snow will fall at higher elevations without the blizzard conditions that plagued mountain communities in late February.
- Expect rain in all mountain communities and resorts, which could combine with several feet of snow from the last storm to cause problems.
A storm fed by an atmospheric river over the Pacific Ocean will bring rain and snow Friday and possibly into the weekend in Southern California.
No watches or warnings have been issued ahead of the storm, a warmer system that won’t bring as much precipitation as the late-February cold storm that brought a rare warning for blizzards, mudslides, flooding and other weather-related issues. Flooding due to more significant rainfall is expected in Northern California, where residents are still dealing with the aftermath of previous storms.
The next system will draw moisture from an atmospheric river over the ocean. The long columns of moisture contributed to some of the most powerful storms on record in California, including the system that brought record snowfall to the mountains of Southern California and rainy days elsewhere.
Here’s what to expect from the storm.
Atmospheric rivers play an important role in the movement of moisture around the world and can make or break the rainy season in California. When a strong atmospheric river points toward southern California, we can see significant rainfall. Meteorologist David Biggar shows just how common they are and how they can affect our weather.
The system will arrive in Ventura County Thursday night, likely around 11 p.m., before moving to Los Angeles County around midnight. Most areas will see rain through Friday, but the intensity will vary from fog and light rain to brief, moderate to heavy showers.
“Tomorrow morning we are going to start with wet roads,” said NBC4 meteorologist Belén De León. “Rain moving in late afternoon (Thursday) and tonight for Ventura County. By tomorrow morning, we’ve got those slick roads.”
Here is the storm timeline.
- Ventura County: Thursday from 11 pm to Friday at 10 pm
- Los Angeles County: 12 a.m. Friday to 10 p.m. Friday
- Orange County: 2 a.m. Friday to 10 p.m. Friday
- Inland Empire: 3 a.m. Friday to 11 p.m. Friday
“The heaviest rain will be moderate,” De León said. “We don’t expect large rates of rainfall.
“By Saturday, we are starting to see the intensity of the rain recede. It looks like a mostly cloudy day with drizzle.”
Here are the projected rainfall totals.
- Ventura County: 0.50 to 1.50 inches
- Los Angeles County: 0.25 to 0.75 inches
- Orange County: 0.25 to 0.75 inches
- Inland Empire: 0.25 to 0.75 inches
- Ventura County Mountains: 1 to 2 inches of rain
- San Gabriel Mountains: 0.25 to 0.50 inches of rain
- San Bernardino Mountains: 0.25 to 0.50 inches of rain
Another storm is expected to hit the region early next week.
Previous storms driven by atmospheric rivers have already pushed Los Angeles past its seasonal rainfall average. Throughout the state, the most severe drought conditions have been eliminated.
Projected Snow Levels
Unlike the cold storm in February, when snow levels dropped to unusually low elevations, snow levels with this storm will remain well above 10,000 feet. Only a few peaks in the San Bernardino Mountains, where residents are still digging after the previous blizzard, will receive snow.
Expect rain in all mountain communities and resorts, which could combine with several feet of existing snow to cause problems including roof collapse, increased avalanche danger, and heavy runoff.
An avalanche on March 1 blocked a stretch of mountain road at Mount Baldy. Mount Baldy Resort tweeted that avalanches were reported in the Movie Slope area.
No injuries were reported.
Rapid snow flows coming down a mountain kill more than 150 people worldwide each year, according to the National Weather Service.
Warning signs include cracks in the snow around your feet or skis; a feeling of emptiness in the ground underfoot; ‘thumping’ sounds indicating snow settling; heavy snowfall or rain in a 24-hour period; rapidly rising temperatures; and patterns in the snow created by the force of high winds.
In the mountains of San Bernardino County, unrelenting snow blocked roads and left some residents stranded without supplies. Snow piled up to rooftops in Lake Arrowhead and other communities. In Crestline, the roof of a family-owned grocery store collapsed under the weight of the snow.
NASA’s Terra satellite shows snow on the SoCal mountains. Melissa Magee reports for NBC4 News.
Northern California storm and Sierra Nevada snowpack
The storm will have more severe implications for Northern California, where heavy rain, high winds, thunderstorms and the threat of flooding are possible in communities already hit by previous storms.
The flood threat will come from a combination of rain and melting of parts of the massive snowpack formed in the California mountains by nine atmospheric rivers in early winter and subsequent storms fueled by a blast of arctic air.
Snowpack at high elevations is so massive that it should be able to soak up rain, forecasters said. But elevations below 4,000 feet will see melt and runoff. At high elevations, the storm was predicted to dump heavy snow, up to 8 feet in some places.
Snowpack in California’s Sierra Nevada, which provides about a third of the state’s water supply, represents more than 180% of average on April 1, when it is historically at its peak. Ideally, the snowpack melts in the spring and summer, then runs off into the state’s extensive water supply system.
So much snow has fallen on the Sierra and other mountain ranges that residents are still struggling to dig out days after previous storms. Roofs collapsed, cars were buried, and roads were blocked. Governor Gavin Newsom declared emergencies in 13 of California’s 58 counties effective March 1.
Associated Press contributed to this report.