‘Powerful’ Atmospheric River Sparks California Avalanche Warning

A powerful atmospheric river dumping feet of snow and heavy rain over the Pacific Northwest has sparked the Mount Shasta Avalanche Center to issue an avalanche warning for part of Northern California.
A bomb cyclone churning over the Pacific ushered in atmospheric river conditions and winds equivalent to a hurricane when it hit the Pacific Northwest earlier this week. The storm’s impacts have since started to move east to affect the Intermountain West, but some dangerous weather conditions remain in place across California, according to the National Weather Service (NWS).
A bomb cyclone occurs when a storm’s pressure drops quickly, which intensifies the storm and ramps up wind gusts. Northwest of Washington, winds gusted as high as 101 mph on Vancouver Island, AccuWeather reported, equivalent to a Category 2 hurricane. Winds measured 85 mph in parts of Oregon, equivalent to a Category 1 hurricane.
Up to an additional foot of snow is expected to fall across Northern California through Wednesday evening. Heavy snow prompted an avalanche warning for Mount Shasta in south-central Siskiyou County.
“An exceptionally powerful atmospheric river will impact the Mount Shasta region. Prolonged periods of heavy snowfall, along with rain-on-snow will create high avalanche danger,” the Mount Shasta Avalanche Center said in the warning, which was broadcast by the NWS office in Medford, Oregon.
The warning is in place for the avalanche terrain of Mount Shasta, Castle Lake, the Eddy Mountains and the Ash Creek Butte area east of the mountain.
The warning will remain in effect until noon local time on Thursday.
“Intense rainfall and multiple feet of new snow will produce large and destructive avalanches. These avalanches may run long distances into flat terrain, valley floors, and mature forests,” the warning said. “In addition, debris flows are possible out of Mount Shasta drainages such as Cascade Gulch, Ash Creek, and Mud Creek.”
NWS meteorologist Mike Stavish told Newsweek that an avalanche warning this early in the winter season is “unusual.”
“It is an early-season snow event, that’s for sure,” he said. “It’s not really common to get events this heavy this early in the season.”
The warning went on to say that travel near the area was not recommended, given the “very dangerous avalanche conditions.”
“Recreational users without backcountry avalanche skills are advised to stay out of the backcountry. Deep snow conditions exist,” the warning said.
In addition to the avalanche warning, a winter storm warning, wind advisory, winter weather advisory and other winter weather-related alerts remain in place in California.