California: powerful ‘atmospheric river’ storm prompts evacuation warnings

A powerful storm doused California with heavy rain on Friday, prompting evacuation warnings as the state braced for the potential of floods, mudslides, thunderstorms and even the chance of a tornado over the weekend. More than 4in of rain fell over coastal Santa Barbara county as the storm moved south toward Los Angeles, according to the National Weather Service. Communities in Santa Barbara, Ventura and Los Angeles counties – especially those near burn scars where there are higher risks for mudslides and debris flows – could be in for a dangerously wet weekend, with two surges of rainfall expected through Sunday. As communities prepared for Saturday’s expected storm surge, evacuation warnings were issued through Sunday morning in areas affected by recent wildfires, including those by the major blazes in Los Angeles in January. Forecasters with the National Weather Service in Los Angeles warned that roads and highways would likely see flooding along with debris flows that could block thoroughfares and damage infrastructure. “In creeks and rivers, the flows will be heavy with anyone in or near those channels at risk of being swept away,” officials wrote in a Friday morning update. Some uncertainty about timing and location of the most intense effects remained, with the possibility that the storm could stall over a particular area for an extended period of time. “Wherever it sets up, expect all these impacts to be amplified, including a risk for a neighborhood or two experiencing shallow water spilling into businesses and homes,” forecasters warned. “In addition to the water risks, there is a significant threat for severe thunderstorms capable of producing very localized but damaging winds and or a brief tornado.” From 2in to 5in of rain is predicted to fall across low-lying areas of southern California in 48 hours, according to the NWS. This event could mean downtown Los Angeles would face its wettest November since the 1980s. Along the coastal slopes, the predicted totals are even higher – rain along the Transverse ranges could surpass 6in by Sunday. The extreme weather has already led to closures and disruptions. Tyler, the Creator, a musician, postponed his festival set to take place at Dodger’s Stadium this weekend due to stormy conditions. Local amusement parks Knott’s Berry Farm and Six Flags Magic Mountain shut their gates in anticipation of the storm, and Topanga Canyon Boulevard, a mountain thoroughfare that was heavily hit by the Palisades fire at the start of the year, closed at 10pm on Thursday due to high risks of debris flows there, according to the California department of transportation. While major damage has not yet been seen, a large downed tree smashed a car in an LA neighborhood on Friday morning, local news outlets reported. No injuries were reported. These types of powerful rainstorms, known as atmospheric rivers, have long been important features of weather systems across the US west and are vital to replenishing the state’s reservoirs and snowpack. The rains are expected to provide at least some relief for parched landscapes and the high fire risks that linger into autumn. But filled with enough moisture to rival the volume of the flow at the mouth of the Mississippi – and often many times more – the strong systems that carry water across the Pacific can often cause the most destructive floods. The second surge, which is predicted to start on Friday night into Saturday, is causing the most concern. While it was still unclear how much rainfall would hit specific parts of the state and when, forecasters with the National Weather Service in Los Angeles said there was a “growing risk for significant impacts on Saturday including dangerous flooding, damaging debris flows and major road closures”, and urged residents to heed advice from local officials. “Saturday would be a great day to plan indoor activities & avoid traveling if possible to stay safe,” the National Weather Service in Los Angeles posted with a forecast update on Thursday evening. Heavy snow is also expected, with up to a foot dumped along the slopes of the Sierra Nevada and up to 18in along the highest peaks. Most of the dangers have passed in the San Francisco Bay Area, and officials allowed previously issued wind and flood advisories to expire on Thursday evening. The strongest gusts of wind reached 80mph in Marin county. But there is more rain in the forecast for next week. “Cooler, wetter weather remains on tap as multiple systems pass through the region this weekend into next week,” the NWS Bay Area said. The Associated Press contributed reporting