Southern California is bracing for a potentially historic storm system, described by forecasters as possibly the worst Christmas storm in recent memory. An atmospheric river is already bringing heavy rain, strong winds, and significant snowfall to the region, and the impacts are expected to intensify through the week.
Widespread Risks and Warnings
Meteorologists at the National Weather Service’s Oxnard office warn this is a “long-duration event” with “cumulative effects of rain.” Ariel Cohen stated, “It might be best to stay indoors during this event,” emphasizing the potential for life-threatening flooding and dangerous mudslides. The National Oceanic and Atmospheric Administration’s Weather Prediction Center has elevated the flash flood risk to high for Wednesday across a large area of southwest California, including the L.A. Basin, Santa Clarita, Thousand Oaks, and Santa Barbara.
Kristan Lund, a meteorologist with the National Weather Service in Oxnard, warned of potential hazards including cars being swept away, structural flooding, downed trees, power outages, and significant travel disruptions.
Timeline of Expected Impacts
Rainfall is expected to increase Tuesday evening and overnight. While flooding isn’t an immediate concern then, high winds and intense rainfall rates are possible. Wednesday will see a potential lull in the heaviest rainfall during the day, but a second, stronger band of precipitation is forecast to arrive Wednesday evening and continue through Thursday morning, significantly increasing the risk of urban flooding, debris flows, and mudslides, particularly in areas previously affected by wildfires.
Thursday is expected to bring continued heavy rainfall and ongoing flood concerns. Lingering showers are possible Friday and Saturday, adding to already substantial rainfall totals. Temperatures are forecast to drop, potentially bringing several inches of snow to the San Bernardino and L.A. County mountains by the weekend.
While snow will be less of a concern in the Southern California mountains earlier in the week, the Sierra Nevada is forecast to receive 3 to 5 feet of snow, creating “major impacts to mountain travel.”
Coastal areas and valleys in Southern California are forecast to receive 4 to 6 inches of rain through Saturday, while foothills and mountains could see up to 10 inches.
Frequently Asked Questions
What areas are at highest risk of flooding?
The southern slopes of the Santa Monica, San Gabriel, and San Bernardino mountains are at high risk for flash flooding, as is much of the L.A. Basin, Santa Clarita, Thousand Oaks, and Santa Barbara.
When is the most dangerous period expected to be?
Wednesday evening through Thursday morning is expected to bring the highest risk of urban flooding, debris flows, and mudslides due to a second band of heavy rainfall.
What about travel?
Travel is expected to be significantly impacted throughout the region, with potential delays in the air and on the roads. Mountain travel across the Sierra Nevada will be particularly hazardous due to heavy snowfall.
As this storm system develops, residents should remain vigilant and heed the warnings issued by local and national weather authorities.
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