One of the more potent storms of the winter will hit California with heavy rain, excessive mountain snow and gusty winds and overspread a large part of the state during Tuesday night and Wednesday and last into Thursday in some locations.
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 slopes of the mountains. An AccuWeather Local StormMax™ of 6 inches is forecast on the low-elevation, west-facing Coast Ranges north of San Francisco and the lower western slopes of the central Sierra Nevada.
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 5-8 feet of snow is forecast over the Sierra Nevada, above 7,000 feet.
Some of the ridges and peaks of the central and northern Sierra Nevada may be buried under a fresh 10 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 Meteorologist Adam Douty.
Interstate 80 at Donner Summit, California, is likely to be closed for a time.
"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, 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.
In Southern California, a general 1- to 2-inch rainfall 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.
Incidents of urban flooding and mudslides are likely.
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.