Southern California Faces Rare High Risk, Atmospheric River Threatens Flooding
The National Weather Service has issued a rare High Risk outlook for excessive rainfall as a strong Pineapple Express atmospheric river targets Southern California, raising the prospect of widespread, life threatening flash floods and debris flows. Residents in communities north of central Los Angeles should prepare for heavy rain, possible evacuations and disruptions to travel and commerce during the busy holiday period.
The Weather Prediction Center of the U.S. National Weather Service issued a Level 4 of 4 High Risk outlook for excessive rainfall covering parts of Southern California for Wednesday December 24, 2025 through the morning of Thursday December 25, 2025. The High Risk designation signals a high probability of widespread, life threatening flash flooding as a strong atmospheric river known as a Pineapple Express carries a long plume of tropical moisture onshore.
Forecast products and satellite imagery show the moisture laden plume over the eastern Pacific at 00 00 UTC on December 23, 2025, underscoring the scale of the event. Forecasters expect the system to move onshore beginning late Tuesday and to continue through Thursday morning, with some local forecasts noting rain beginning Tuesday afternoon and intensifying Tuesday night into Wednesday. The timing differences do not alter the consensus that the heaviest precipitation will occur on Wednesday December 24, the period covered by the WPC High Risk outlook.
The greatest vulnerability is a corridor north of central Los Angeles, with communities named in local advisories including Burbank, Altadena, Glendale, San Bernardino, Santa Clarita and Thousand Oaks. Officials and forecasting agencies emphasize that areas below recent wildfire burn scars face acute risk of mudslides and debris flows as saturated ground can fail suddenly under heavy rainfall. Evacuation information and maps were posted for parts of Los Angeles County as of December 22, 2025, and county officials implemented evacuation warnings and orders in some locations ahead of the storm.
The rarity of a High Risk classification underscores the severity of the threat. WPC High Risk is reserved for situations with a high probability of large scale, dangerous flash flooding and is issued infrequently. The alert comes amid broader unusual severe weather activity in December 2025, with other rare National Weather Service advisories issued in different regions earlier this month, reflecting a volatile pattern of storms across the western United States.
Beyond immediate life safety concerns, the storm presents near term economic and logistical risks. Heavy rainfall and flash flooding can knock out transportation links, force airport and road closures, disrupt retail activity during a critical holiday period and impose rapid emergency response costs on local and state agencies. Debris flows and infrastructure damage in burn scar areas can require costly post storm remediation and prolong disruptions to homes and businesses. Local governments and Cal OES will play central roles in coordinating evacuations, shelters and debris flow mitigation, while county flood control agencies monitor channels and critical infrastructure.
The event also feeds into longer term policy questions about resilience. Intensifying atmospheric river events have become a focal point for discussions about upgrading stormwater systems, accelerating burn scar stabilization work and rethinking land use in vulnerable foothill and canyon communities. As the storm unfolds, officials will need to balance immediate protective actions with planning for bigger investments to reduce the fiscal and human toll of future extreme precipitation events.
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