This AccuWeather Enhanced RealVue™ Satellite image from Wednesday morning, December 11, shows a train of storms approaching the West Coast.
Storms are lining up like freight cars on the Pacific Ocean, ready to bring rain, mountain snow, and gusty winds, potentially leading to travel disruptions across Washington and Northern California. According to AccuWeather meteorologists, at least one of these storms could develop into a bomb cyclone.
“Storms are set to arrive in the Northwest every two to three days, likely continuing until December 22 or just before Christmas,” said AccuWeather Senior Meteorologist Brett Anderson.
One or more of these storms could form a long plume of moisture known as an atmospheric river, often referred to by meteorologists as an “atmospheric firehose.”
The first storm will begin to roll in Wednesday night, impacting Oregon and Northern California.
“For much of Northern California, this will be the first rain since before Thanksgiving,” said AccuWeather Senior Meteorologist Dave Houk. “The heaviest rain from this first storm will hit Wednesday night, moving quickly south through the San Francisco Bay area by the middle of the night and down the coast of Central California before dawn on Thursday.”
Northern California and parts of western Oregon can expect between 0.50 and 1 inch of rain. The rain intensity will decrease farther south, but a couple of hours of rain could still reach Los Angeles on Thursday.
Later this week, storm number two will approach Washington and British Columbia.
“This second storm has the best chance of rapidly intensifying into a bomb cyclone,” Houk said.
A bomb cyclone occurs when a storm’s central pressure drops by 0.71 of an inch of mercury (24 millibars) or more in 24 hours or less.
Rain will spread across much of Washington and Oregon on Friday, reaching the coast of Northern California, including the San Francisco area, by Friday night and Saturday.
“In Northern California, along the coast and into the mountains, rainfall amounts could range from 2 to 4 inches, raising the risk for flooding in low-lying areas, creeks, and streams,” Houk warned.
The mountains will also see significant snow with at least the first two storms and likely more.
“Snow levels in the Klamath Range could accumulate up to 1 foot above 3,500 feet, causing travel delays on the higher elevations of Interstate 5. Donner Pass in California, on I-80 in the Sierra Nevada, could see 6 inches of snow, leading to difficult travel Wednesday night and Thursday morning,” Houk explained. “The second storm will bring another round of heavy snow, but snow levels will rise briefly Friday night before dropping again Saturday. Some places could get an additional 1-2 feet of snow from the second system.”
After a break on Saturday, storm number three is expected to arrive Sunday in the coastal Northwest, reaching San Francisco by Monday morning, which could cause slow traffic during rush hour.
More storms will follow.
“While the end of most storms will bring moisture to Southern California, it’s unlikely any of them will produce significant rain that far south,” Houk cautioned.
November saw near-average rainfall and mountain snow in Northern California, but much of Southern California experienced sparse rain, well below the historical average.
Abnormally dry to moderate drought conditions have been gradually worsening in parts of California and the Southwest.
The final storm in the series may be strong enough or track far enough south to bring significant rain and mountain snow to Southern California before Christmas.
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