A powerful Pineapple Express storm could deliver a wet, white and potentially wild Christmas to California, with the possibility of snow in the Sierra Nevada and plenty of rainfall across Southern California.

The incoming atmospheric river system is shaping up to be the strongest in years to hit the Los Angeles area on the holiday — and threatens a soggy slog for those hitting the road to visit friends or family.

The peak of the storm for Southern California is likely to start Tuesday and continue through Christmas Eve and Christmas Day, according to Bryan Lewis, a meteorologist with the National Weather Service office in Oxnard.

The most likely scenario for Los Angeles, Ventura, Santa Barbara and San Luis Obispo counties involves "high amounts" of rain: 2 to 4 inches on the coast and in the valleys. There's a 50% chance of that scenario coming to pass.

There's also a 30% chance of "very high" amounts of rainfall, 4 or more inches, on the coast and in the valleys.

The last time it rained on Christmas Eve or Christmas Day in downtown L.A. was in 2021, when 0.83 inches fell over the two days. The last time it rained more than 2 inches over those two days was in 1971.

It's still unclear whether this storm will be naughty — with torrential downpours intense enough to cause flooding and mud or debris flows — or nice, with gentle rainfall spread out beneficially over a period of days.

However, "overall, the storm seems to be trending towards a higher rainfall total and higher rates than what we were seeing yesterday," Robbie Munroe, a meteorologist with the National Weather Service office in Oxnard, said Thursday.

It's still early, but the storm appears to have the ingredients for "a concerning situation we're keeping an eye on," Munroe said. Forecasters will need to wait until the weekend before they'll have a better sense for how much rain will fall per hour, a key factor in forecasting the risk of mud and landslides.

More problematically, this storm could turn out to be the first of a sequence, with one or even two more looming in its wake. There's a growing potential for moderate to locally heavy showers continuing into Dec. 27.

"This might be the first of two or three storm systems," Munroe said. "And if that does happen, impacts could become more concerning for that period of time, possibly lasting as we close into the new year, even."

Beyond the Christmas storm, there's a lot of energy and moisture in the Pacific Ocean, Munroe said.

Although the storm promises to bring Southern California's first significant soaking in a month, an interlude that followed one of the region's wettest Novembers on record, Northern California was already hit by storms this week.

A brief lull was expected Thursday, with a parade of storms forecast to begin by that night. Localized flooding could hit the North Coast on Thursday night into Friday, while light to moderate rain was expected in San Francisco and Sacramento.

The San Francisco Bay Area is expected to see its first in a series of Christmas week storms on Sunday, potentially snarling holiday travel.

"By the beginning of next week, we are likely to see rivers begin to swell and the potential for rock and land slides to interfere with travel plans," said the National Weather Service office in Monterey, which issues forecasts for the Bay Area.

"This atmospheric river pattern will bring significant amounts of rain," said the weather service office in Sacramento. Snow levels could drop to 5,500 feet above sea level by Tuesday and Wednesday, suggesting "potential major mountain holiday travel impacts" for Christmas Eve.

The storm is slated to come from the tropics southwest of the California coast. It's expected to start out as a warm storm, and some ski resorts in Los Angeles County might initially see rain instead of sought-after snow.

"There is the potential that they could get a fair amount of snow at the resort level later on Christmas Day ... or into the 26th, or even beyond, if the active weather pattern continues," Munroe said.

In the Sierra, where resorts have been pained by warm weather and a snow drought so far this season, it was far from clear whether there would be enough cold air to lower snow levels.

"This system will be drawing up copious amounts of subtropical moisture from the south," Bryan Allegretto wrote in the weather blog for Palisades Tahoe.

Allegretto said he has been nervous about the system of low pressure being too far away from California. To get more snow in California's mountains, "we need the cold air at the center of the trough and the low to push inland," and computer forecasting models are split on whether that will happen, he wrote.

"Let's hope the trend is towards the storm progressing inland and dropping snow levels to the base quickly on Christmas Eve," Allegretto wrote. "If we get the colder air, then we could see significant snowfall."

In Southern California, it's unlikely that the Christmas week storm will cause snow to fall on the Grapevine section of the 5 Freeway. Snow is possible above 5,500 feet in Los Angeles County late on Dec. 25 and into the weekend, while the highest section of the Grapevine, Tejon Pass, is at an elevation of 4,144 feet.

In Orange County, the Inland Empire and San Diego County, light showers may start on Tuesday, but the day of the heaviest rainfall is expected to be on Christmas Eve, said meteorologist Adam Roser with the National Weather Service office in San Diego.

Light-to-moderate showers are expected for Christmas Day for that region, Roser said.

In the San Bernardino Mountains, snow levels are expected to remain high, likely over 8,000 feet. The elevation at the city of Big Bear Lake is 6,752 feet above sea level.

"Confidence continues to increase that bouts of heavy rainfall will lead to an increased flood and debris flow risk, as well as holiday travel disruptions for the entire region," the weather service office in San Diego said.

©2025 Los Angeles Times. Visit latimes.com. Distributed by Tribune Content Agency, LLC.