The powerful storm that walloped California over the past two days delivered record-breaking rains, feet of mountain snow and damaging winds. Atmospheric river slams Southern California, then stalls Atmospheric river slams Southern California, then stalls An atmospheric river — a narrow but intense jet of Pacific Ocean moisture — parked itself over the Los Angeles area on Sunday, and the rain was still falling Tuesday. A flash flood warning for the Santa Monica Mountains and the Hollywood Hills, which have been hard-hit by flooding and mudslides, was to remain in effect until 10 a.m. Tuesday. Nearly 12 inches of rain has fallen in several locations, including in Bel Air and Topanga Canyon near Malibu, though the heaviest rains were shifting to the east and south. This storm is a “top-tier” rainfall event for the Los Angeles area, according to Joe Sirard, a meteorologist with the National Weather Service office in Oxnard, Calif. Downtown Los Angeles recorded 7.03 inches of rain on Sunday and Monday, the third highest for any two-day period since 1877 and the most observed in February. “That’s a lot of years of record, and for this to be the third-most ever in a two-day period for downtown Los Angeles is hugely significant,” Sirard said. The episode even reached the threshold of a 1,000-year rain event at a gauge at the University of California at Los Angeles, where 12.46 inches fell in 24 hours. That means that so much rainfall had only a 0.1 percent chance of happening in any given year. The extreme totals aren’t surprising, given the prolonged and nearly continuous heavy rain across much of Los Angeles County. “You can get a huge impact on one area and relatively little to the north or south,” said Alison Bridger, an atmospheric scientist at San José State University. “There can be quite a narrow focus with an atmospheric river.” But Californians know these storms are also essential, with years of painful drought a not-so-distant memory. “You have to remember that it just doesn’t rain at all in summer, so we really need to squeeze as much rain and snow out of these storms as we can,” she said. Bomb cyclone drives damaging winds Bomb cyclone drives damaging winds The storm was in some ways a tale of two regions, with Northern California seeing the brunt of the winds while Southern California has been battered by floods and mudslides. “Not only did we get the atmospheric river part — which is just the water vapor slamming into the mountains — but we had the larger wind field with the very strong storm system that accompanied it,” said Jay Cordeira, an atmospheric scientist with the Center for Western Weather and Water Extremes at Scripps Institution of Oceanography. The storm’s low-pressure center — dubbed a “bomb cyclone” because of how rapidly it intensified — set up a steep change in pressure over a short distance, driving the ferocious winds. The Weather Service said the pressure gradient between Los Angeles and San Francisco nearly reached an all-time high, an indicator of how strong and dangerous the storm was. Wind gusts topped 100 mph in some spots, but readings above 70 and 80 mph were widespread, especially in the northern and central parts of the state. San Francisco International Airport clocked a gust of 77 mph. The relentless gusts toppled trees and power lines, leaving nearly 1 million customers statewide without power at one point on Sunday. The outages prompted the California Independent Systems Operator (Caiso) to declare a “transmission emergency” on Sunday to protect the electrical grid from possible cascading failures although the system as whole remained secure, according to Caiso spokesman Oscar Hidalgo. About 150,000 customers were still without power early Tuesday. Bridger said that while bomb cyclones aren’t uncommon, it was somewhat unusual for one to intensify so far south and so close to the California coast. A similar system impacted Northern California last March. “Normally I would expect these more up in the Gulf of Alaska or impacting British Columbia and Seattle,” she said. El Niño and climate change connection El Niño and climate change connection This week’s storm resembles those of past notorious El Niño winters, but it’s difficult to say just how much influence the tropical oceanic pattern is exerting. “What we can say is that the increased California rainfall is certainly consistent with a strong El Niño,” said Michelle L’Heureux, a climate scientist with the National Weather Service’s Climate Prediction Center. The jet stream is racing across the southern tier of the United States — a typical El Niño signature, L’Heureux said — bringing severe weather and heavy downpours as far east as Florida this week. El Niño’s impacts also often materialize between January and March. Abnormally warm waters off the coast of California and in the Pacific Ocean are probably supercharging precipitation, mirroring a global trend of record-breaking water temperatures. “There is this fairly broad consensus that it’s not just El Niño operating in isolation. There is also climate change operating on top of that,” she said. Wet extremes during El Niño become even wetter because there is more water vapor available in the atmosphere in a warmer world. Atmospheric rivers are also predicted to become more extreme as the climate warms, with a sharp increase in rainfall rates. “These atmospheric rivers that aggregate and take advantage of the water vapor in the atmosphere will be stronger and wider and more intense at landfall,” Cordeira of Scripps said. “As we move forward, we’d expect atmospheric rivers to be more impactful.” Matthew Cappucci and Jason Samenow contributed to this report.