A powerful Pineapple Express storm could bring a wet, white and potentially wild Christmas to California, with possible snow in the Sierra Nevada and significant amounts of rain across the South.
While weather forecasts remain a concern, an upcoming atmospheric river system set to hit the Los Angeles area during the holidays will be the strongest in years and could cause soggy difficulties for those taking to the road to visit friends or family.
Robbie Munroe, a meteorologist with the National Weather Service’s Oxnard office, said Los Angeles, Ventura, Santa Barbara and San Luis Obispo counties are most likely to see “significant” amounts of rain: 2 to 4 inches along the coast and in the valleys between Dec. 24 and 26.
The probability of this happening is 50%.
The Coast and Valleys also have a 30 percent chance of moderate rainfall, or 1 to 2 inches, while those areas have a 10 percent chance of “very high” rainfall, or 4 inches or more.
The last time it rained on Christmas Eve or Christmas Day in downtown Los Angeles was in 2021, when 0.83 inches fell over two days. The last time more than 2 inches of rain fell in those two days was in 1971, according to Bryan Lewis, a meteorologist with the weather service’s Oxnard office.
It’s unclear whether the storm will be naughty, with enough downpours to cause flooding and mudslides, or moderate rain that will spread favorably over several days.
“Even if we see very high totals, the impact will likely still be mild to moderate,” Monroe said at a news conference Wednesday.
(National Weather Service)
But more problematically, the Christmas week storm could be just the first in a series, with one or even two more looming.
“This could be the first of two or three storm systems,” Monroe said. “If this does occur, the impacts during that period could become more concerning and could even last into the New Year.”
Monroe said there’s plenty of energy and moisture in the Pacific in addition to the Christmas storm, “but it’s hard to know whether it will come in the form of one larger storm or two or three” milder systems.
While the storm is expected to bring widespread rain to Southern California for the first time in a month, an episode that follows one of the region’s wettest Novembers on record, Northern California has already been battered by storms this week.
A brief lull is expected on Thursday, with a series of storms expected that evening. Isolated flooding is possible on the North Coast Thursday night into Friday, with light to moderate rain expected in San Francisco and Sacramento.
The San Francisco Bay Area is expected to be hit by the first of a series of Christmas week storms on Sunday that could disrupt holiday travel.
“By early next week, we may see rivers begin to rise and rock and land slides may disrupt travel plans,” said the National Weather Service office in Monterey, which issues weather forecasts for the Bay Area.
“This atmospheric river pattern will bring significant rainfall,” the Sacramento weather service office said. Snowfall amounts could drop as low as 5,500 feet above sea level by Tuesday and Wednesday, suggesting Christmas Eve “may be impacted by significant mountain holiday travel.”
The storm is expected to come from the tropical southwest of the California coast. Expected to start with a warm storm, some ski resorts in Los Angeles County may initially see rain instead of the welcome snow.
“If the active weather pattern continues, resorts could see significant amounts of snow later on Christmas Day, or into the 26th, or even beyond,” Munroe said.
In the mountains, resorts have been hit by warm weather and snow drought so far this season, and it’s unclear whether there will be enough cold air to bring down snow amounts.
“This system will draw a lot of subtropical moisture from the south,” Bryan Allegretto wrote on the weather blog Palisades Tahoe.
Allegrito said he had been nervous about the low-pressure system being too far away from California. To get more snow in California’s mountains, “we need cold air and low pressure in the center of the trough to push it inland,” he wrote, and computer forecast models are divided on whether that will happen.
“We’re hoping the storm will trend inland and quickly bring snow levels to their lowest point by Christmas Eve,” Allegretto wrote. “If we get colder air, then we could see heavy snow.”
The storm’s temperatures could impact traffic on major corridors. The colder storm could cause snow accumulation on the Grapevine section of Highway 5 and on Tehachapi Pass, which connects Bakersfield to the Mojave Desert.
In Orange, Inland Empire and San Diego counties, the heaviest rainfall is expected late on Christmas Eve and on Christmas Day, according to the National Weather Service office in San Diego.
“But if the system stalls completely or remains far from the coast, the timing of the heaviest rainfall may be delayed, with rain likely to continue into next Friday or longer,” the weather service said. “There is growing confidence that heavy rainfall will lead to an increased risk of flooding and mudslides, as well as disruption to holiday travel across the region.”
