Summarize this content to 2000 words in 6 paragraphs Rain fell across Northern California on Saturday and could continue for days with an atmospheric river hanging over the region like a sopping wet towel.With multiple pushes of moisture expected, parts of the region could see continuous soggy weather into next week, potentially through Friday, and a heightened risk for flooding that could increase as the ground becomes increasingly saturated.Through Friday, the coastal mountains are expected to record six to 15 inches of rain, and the northern Sierra Nevada could see multiple feet of snow, according to the Weather Prediction Center.Snow fell in the Sierra Nevada and Cascade Ranges on Saturday, but only at the highest elevations as the system that is pulling in moisture from the subtropics near Hawaii is warm. This kind of atmospheric river is often referred to as a pineapple express.With the arrival of the atmospheric river, the storm door has opened in Northern California.“It’s a steady stream of moisture that’s being channeled from the Pacific Ocean into California and as it moves inland, it’s fueling periods of moderate to heavy precipitation,” said Frank Pereira, a meteorologist with the Weather Prediction Center.Forecasters had originally said two separate atmospheric rivers would hit the West Coast, but by Saturday, it was difficult to tell one from the other.“I think more important than identifying a second storm is really the continuous atmospheric river conditions,” said Julie Kalansky, deputy director at the Center for Western Weather and Water Extremes at Scripps Institution of Oceanography at the University of California, San Diego.The Pacific Northwest is also picking up some precipitation and off-and-on rain and snow. Showery weather is forecast for the region through the weekend and into the week but Northern California is in the bull’s-eye for the wet weather.The heaviest rain is expected in the San Francisco Bay Area, north into Mendocino and Humboldt Counties, across the northern valleys and into the northern Sierra Nevada, especially the foothills.The highest elevations of the Sierra Nevada will measure multiple feet of snow over the next week, with isolated locations pushing six to nine feet of snow, said Amanda Young, a meteorologist with the National Weather Service office in Reno, Nev.Ms. Young said on Saturday that snow was falling in the northern Sierra at elevations of 7,000 feet to 8,000 feet and above, and rain was falling below that. The altitudes at which it will snow are expected to drop to 6,000 feet, or even a little lower, early next week with lower temperatures, she said.Flood watches were in effect for a good portion of Northern California on Saturday and were expected to continue through the weekend and potentially early next week.There is a marginal to slight risk of excessive rainfall that could lead to flooding across portions of coastal California and the northern Sierra Nevada through Wednesday.“That’s unusual to see that for that many days in a row,” said Matt Mehle, a forecaster with the National Weather Service office in Monterey, Calif.Mr. Mehle said the San Francisco Bay Area has a chance for rain in the forecast every day between Saturday and Friday.The uptick in storm activity comes after Northern California saw multiple weeks of dry weather.Because of the lack of rain in January, the flood risk from heavy rainfall will likely be less than what it would have been if precipitation were average in recent weeks, said Daniel Swain, a climate scientist with the University of California, Los Angeles.“This rain will be falling on relatively dry-for-February soil,” Mr. Swain said. “In Northern California, the first couple of inches will be largely absorbed by the soil.”As the moisture flow spreads south, Southern California, where deadly wildfires ravaged the landscape last month, is expected to see a chance for rain Tuesday through Friday.David Gomberg, a meteorologist with the National Weather Service office in Oxnard, Calif., said on Saturday that it was too early in the forecast to nail down the risk of debris flows in areas burned by fires, but some risk is possible.“It’s not going to be continuous rainfall, but there will be periods of rain across those days,” Mr. Gomberg said.
