Los Angeles County faces significant risks of flooding and landslides as the region prepares for its first substantial rainfall of the winter. Recent wildfires have left areas vulnerable to debris flows, prompting warnings from the National Weather Service.
Areas scarred by recent wildfires in Los Angeles County are facing a heightened risk of flooding and landslides as Southern California braces for its first significant rainfall of the winter this weekend. The National Weather Service (NWS) office in Oxnard emphasized the severity of the threat, urging preparedness for worst-case scenarios.
Forecasters predict a 10% to 20% chance of substantial flash flooding and debris flows capable of inflicting damage on roads and homes in vulnerable areas recently ravaged by wildfires. These areas include the burn scars of the Palisades and Franklin fires surrounding Pacific Palisades and Malibu, the Eaton fire around Altadena and Pasadena, the Hughes fire near Lake Castaic, and the Bridge fire within the Angeles National Forest north of Glendora.The Bridge fire, which scorched over 56,000 acres across Los Angeles and San Bernardino counties in the autumn, destroyed 81 structures and injured eight firefighters. According to a U.S. Geological Survey assessment, these burn scars exhibit the highest potential for significant debris flows, as stated by Ryan Kittell, a meteorologist with the NWS. Kittell explained that these areas are characterized by their recent burn dates, proximity to communities and vital infrastructure, and terrain orientation, which amplifies the risk of heavy rainfall and intense flows.The probability of flooding and debris flow in these recently burned areas, issued on Friday afternoon, has escalated from the 5% to 10% chance predicted the day prior. While damaging debris flows are not the most likely outcome, the NWS acknowledges the substantial uncertainty surrounding this storm. Recently burned areas are particularly susceptible to damaging floods and landslides because the intense heat from wildfires hinders water absorption by the soil's top layer. The soil becomes hydrophobic, causing water to flow rapidly downhill, accumulating rocks and debris along the way. This can result in 'mudflows,' where water carries primarily mud, usually less than 15 feet deep, or more destructive 'debris flows,' where water, propelled downhill, picks up rocks, branches, and sometimes massive boulders. Mudflows and debris flows are essentially types of landslides. Kittell stated that while the most likely scenario is the absence of significant debris flows, the possibility cannot be ignored and the message of heightened threat must be amplified. He stressed that the storm's potential for impact warrants careful planning and consideration. Kittell added that the most probable outcome is the occurrence of minor, shallow debris flows with limited consequences. The NWS issued a flood watch for the period of highest risk—from 10 a.m. Sunday through 4 p.m. Monday—specifically highlighting Sunday night as a period of heightened concern. A flood watch signifies that weather conditions are conducive to flooding, although it does not guarantee its occurrence.The NWS recommends avoiding recently burned areas during the watch period, using sandbags to protect property, and ensuring residents who choose to remain have adequate supplies in case road access is impeded. Notably, the planned flood watch does not encompass the Mountain fire burn scar in Ventura County. Light rain had already begun to fall in certain areas of Los Angeles on Saturday afternoon. Rainfall is expected to intensify throughout the afternoon in Los Angeles and Ventura counties, with the peak intensity anticipated between Sunday afternoon and Monday noon for both counties. The rain is likely to be intermittent and of moderate intensity throughout the weekend and into Monday. Alex Tardy, a meteorologist with the National Weather Service office in San Diego, characterized the storm as 'slow-moving and persistent,' emphasizing its tendency to linger and deliver repeated waves of moisture through Monday, resulting in significant rainfall and snowfall. Forecasters have revised their rainfall projections upward due to a low-pressure system originating from Canada moving westward, slightly closer to the coast of Southern California than initially predicted. This shift has amplified the storm's potential for moisture and, consequently, increased concerns about debris flows in vulnerable burn scars, according to Kittell. However, significant uncertainty persists regarding the storm's precise trajectory and speed, as stated by Kristan Lund, a meteorologist with the National Weather Service in Oxnard
WILDFIRES FLOODING LANDSLIDES RAINSTORMS SOUTHERN CALIFORNIA LOS ANGELES COUNTY
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