California braces for blizzard conditions, possibly biggest snowstorm of season

Prolonged and intense snowfall, high winds and chilly air will be the theme across portions of the West into this weekend, AccuWeather forecasters warn.

Blizzard conditions and potentially the biggest snowstorm of the season are setting up for California's Sierra Nevada during the second half of the week with several feet of snow in the forecast.

Through the end of the week, stormy conditions and a cooler air mass will advance southward into California. Snow levels are expected to come crashing down over the upcoming days, falling to 2,000-3,000 feet across Northern and Central California by late week.

By Wednesday evening, rain will move along the northwestern California coastline and accumulating snow will begin to spread across the higher terrain of far northern areas of the state, including the Klamath Mountains.

In addition to the snow, winds will also pick up across Oregon, northeastern California and northwestern Nevada by Wednesday night. Some locations could have winds blasting from 40-60 mph during this time, raising concerns for blizzard conditions.

In order to meet the definition of a blizzard, blowing or falling snow with winds in excess of 35 mph and visibility less than or equal to one quarter mile need to occur. This dangerous snow and wind combination results in life-threatening, whiteout conditions for travelers.

Heavy snow will expand through the northern and central Sierra throughout the day on Thursday, rapidly accumulating feet of snow in less than 24 hours. At the peak of the storm, snowfall rates can range from 2-4 inches per hour. Across the Sierra Nevada and portions of the Klamath Mountains, the highest chance for 4-8 feet of snow will be above 5,000 feet.

"As the heaviest precipitation moves through Northern and Central California, snow levels will drop over northern regions in particular. It's possible that they could dip as low as 2,000 feet in the Siskiyous Mountains during the worst of the storm," explained AccuWeather Senior Meteorologist Heather Zehr. The worst conditions are likely Friday night.

Major pass roads will be at risk of being shut down for several days, so travel is highly discouraged across any passes or roads across the northern and central Sierra later this week. Between 4-8 feet of snow is projected to fall around Donner Pass, which could take an extended amount of time to clear once hourly snowfall rates decline.

"With heavy snowfall rates, it will be difficult for road crews to keep up, and even major roads are likely to be severely impacted," noted Zehr.

It is estimated that 30,000 cars and 6,200 semi-trucks cross Donner Pass daily when it is open, according to the California Department of Transportation. The looming threat of closure of the region's main thruway to keep travelers safe may mean a temporary impact on the transportation of goods.

Preparation ahead of the storm should be completed before Wednesday night for most areas in Northern California. Anyone who resides in upslope or mountain regions should gather emergency supplies, including food and drinking water, ahead of the storm's arrival in case they cannot leave home for several days.

Power outages are likely as winds gust upwards of 40-60 mph for many locations, creating a potentially dangerous situation for residents without access to a generator. It could take several days for providers to restore power to customers if heavy snow blocks their path and roads are closed.

"In addition to the mountains, locations across the inner valleys and coasts can face breezy conditions which could raise concern for power outages given the saturated ground," explained AccuWeather Meteorologist Joseph Bauer.

Compared to prior events so far this winter season, forecasters say that this week's storm will be notable in terms of snowfall and impacts -- even by Sierra standards.

Factors such as rich moisture in place ahead of the storm with winds out of the southwest will set the stage for a huge snowfall event for the Sierra Nevada. Experts highlight that what makes this storm so unique is the source region of the storm itself.

"This storm is rolling right out of the Gulf of Alaska, which is pumping down cold Arctic air into the region, leading to lower snow levels than we've seen in recent storms," noted Bauer.

The snow water equivalent levels across California are currently pacing at 82 of the historical averages, slightly behind schedule, according to the California Department of Water Resources.

"After a very slow start to the snow season in the Sierra, this storm will not only push snow totals above the historical average so far but likely bring totals to the seasonal averages with two months left in the snow season," explained AccuWeather Chief Broadcast Meteorologist Bernie Rayno.