March has already brought chaos to the West Coast as back-to-back winter storms dropped an unseasonable 100 inches of snow in Southern California, causing at least one death and leaving residents trapped. But this weekend is set to bring even more precipitation as an atmospheric river comes for the whole state.
Currently, Northern and central California can expect a great deal of rain in the coming weekend, causing risky flood conditions. As the rain falls, it is bound to melt the unprecedented amounts of snow. Heavy, wet snow is expected at higher elevations, specifically in Northern California and the Sierra Nevadas, which will lead to deep snowpack and rough travel conditions, according to the National Weather Service. Most of California’s residents were already under weather warnings on Thursday night, and evacuations have already begun in counties such as Merced, Mariposa, and Santa Cruz.
[Related: Earth’s natural air-scrubbing system works better when it’s wetter.]
“It could get really ugly,” David Rowe, a meteorologist with the National Weather Service, told SFGate on Wednesday. “Probably most of the melt will be in the foothills. The snowpack is so deep in the higher elevations, even though we’re expecting a lot of rain, it will probably soak right in at the higher elevations.”
Governor Gavin Newsom had already issued a state of emergency due to weather conditions on March 1 for 13 different counties, but has since expanded the list to include 21 more counties in order to provide storm response and relief efforts to even more regions.
“The state is working around the clock with local partners to deploy life-saving equipment and first responders to communities across California,” Newsom said Thursday. “With more dangerous storms on the horizon, we’ll continue to mobilize every available resource to protect Californians.”
This unprecedented weather is the result of an atmospheric river that’s called a “Pineapple Express.” Atmospheric rivers in general are narrow regions of the atmosphere that bring water vapor from the tropics to the north. Once the 250-375 mile-wide stream of humid air hits landfall, they can bring a great deal of precipitation, but many are relatively weak. The Pineapple Express is especially powerful because the moisture is coming from Hawaii and the tropical Pacific, which can deal a serious blow to the West Coast, according to the National Oceanic and Atmospheric Administration.
In general, some experts believe that atmospheric rivers are getting more powerful due to climate change.
“This is an unrivaled, unparalleled weather event not experienced in several decades, perhaps back to 1969,” Kris Mattarochia, a science and operations officer at the National Weather Service, tells the New York Times.
