Midweek California storm to bury Sierra Nevada under yards of snow, bring flooding risk
By Alex Sosnowski, AccuWeather senior meteorologist
February 13, 2019, 3:12:08 AM EST
One of the more potent storms of the winter will hit California with heavy rain, excessive high country snow and gusty winds through Thursday night.
The worst of the storm is forecast to focus on Central and Northern California with a heightened threat of flooding, mudslides, erosion, power outages and avalanches and road-closing snowfall in the mountains.
Several inches of rain will fall on the lower and intermediate slopes of the mountains. An AccuWeather Local StormMax™ of 6 inches is forecast on the west-facing Coast Ranges north of San Francisco and the lower to intermediate western slopes of the central Sierra Nevada.
Rapidly melting snow, combined with the rain can cause flooding in the short-run streams and rivers that flow out of the mountains.
Motorists should anticipate small stream and urban flooding with significant delays for their commute. Never attempt to drive through flooded roadways or barricades. The water may be much deeper than it appears and/or the road surface beneath the water may have been washed away.
As this moisture is rammed into the mountains at much lower temperatures, a tremendous amount of snow will be unleashed. A general 3-6 feet of snow is forecast over the Sierra Nevada, above 7,000 feet. However, some rain is likely to mix in up to that level as temperatures rise during the height of the storm.
Some of the ridges and peaks of the central and northern Sierra Nevada may be buried under a fresh 8 feet of snow from this storm alone.
"The combination of snow and wind from this new storm and the amount of snow on the steep slopes in the region will result in a high risk of avalanches," according to AccuWeather Senior Meteorologist Adam Douty.
Interstate 80 at Donner Summit, California, is likely to be closed for a time, even though rain may mix in at the height of the storm.
"Some of the resorts may have to close for a time, due to the extreme conditions and road closures," Douty said.
Gusty winds, in some areas approaching 60 mph in low elevations, can be enough to knock over trees in the soggy soil and create blizzard conditions and extensive blowing and drifting snow over the High Country. Winds may reach 100 mph over the ridges.
In Southern California, a general 2- to 3-inch rainfall event is forecast from the storm in the coastal areas. Locally higher amounts are likely in the mountains north of Los Angeles and east of San Diego. Up to 6 inches of rain may fall with the storm on the mountainsides north of Los Angeles.
"Expect incidents of urban flooding and mudslides," according to AccuWeather Senior Meteorologist Dan Kottlowski.
"Evacuations may be needed in recent burn scar locations once again."
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Already about two times the amount of rain has fallen on coastal areas of Southern California since Jan. 1. Rainfall in Northern California since the start of the year generally ranged from near average to twice that of normal.
Snowfall has more than made up from a big deficit in December with many mountain areas now running close to or above average for the season with more big winter storms to go. The depth of the snow cover over the High Country ranges from 6-12 feet as of Monday morning. Within that snow cover, 1-2 feet of water is locked up.
The snowpack over the High Country should go a long way for water supply during the upcoming dry season. The deep snow over the High Country of the Sierra Nevada slowly melts during the spring and summer, which helps to keep streams running and reservoirs full.
Download the free AccuWeather app to see how much rain or snow will hit your area and to receive weather warnings.
Few things reflect the power of nature and weather like avalanches. This week host, Regina Miller talks to Mark Staples, director of the Utah Avalanche Center, and Dan Burnett, Group Mission coordinator for the Summit County Rescue Group in Breckenridge, Colorado. They discuss recent deaths on the slopes, the weather situations that can contribute to an avalanche, the dangers of human interaction, and how best to survive.
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