Updated at 9:20 p.m. ET

A powerful storm system is predicted to pull away from the East Coast by Friday night, but not before wind, rain, snow and flooding batter the upper Mid-Atlantic through New England.

At least five people have died. Among the victims were two children: a 6-year-old boy in Virginia and an 11-year-old boy in New York state, both killed in their homes by fallen trees.

Across the country in Southern California, the region appeared to have dodged significant mudslides in wildfire-stricken areas, after a storm passed through the area without major incident. It is, however, expected to drop several feet of snow on the Sierra Nevadas.

In Boston, the National Weather Service warned of a "very dangerous situation" along the eastern Massachusetts coastline, including Boston, with "wind, wave, surf action on top of tides, 4 foot storm surge." The warning remains in effect until early Sunday.

Along Boston's waterfront, roads and sidewalks were flooded Friday, closing several roads, reports The Associated Press.

Massachusetts Gov. Charlie Baker activated 200 National Guard members to help with the storm. He said the state was "expecting to see more severe flooding issues here than we did in the Jan. 4 storm," when a previous nor'easter hammered the region with snow and rain.

"It's not snow, it's rain, but the rain and the wind, at the rates that we're going to deal with it, mixed with potentially snow in the afternoon, could create some really challenging issues for all of us," Baker said.

The AP reports that "in Duxbury, south of Boston, officials urged people to evacuate as soon as possible, and the fire department was preparing to use a high water rescue vehicle for the first time to help any residents who wind up stuck in homes during high floodwaters."

"This could be one of those storms that goes into the record books," said Kim Buttrick, a meteorologist in Taunton, Mass. "This is a very dangerous storm."

A high wind warning remains in effect for Cape Cod, Nantucket and Martha's Vineyard until Saturday morning, with gusts up to 80 mph.

By early Friday afternoon, 700,000 customers in Eastern states had lost electricity, the AP reports, with the highest numbers in Virginia, Pennsylvania and New York.

High winds also grounded flights throughout the region. By Friday afternoon, FlightAware reported there were thousands of flights cancelled across the country. Its MiseryMap showed most of the misery centered on New York and New England.

Widespread nausea was reported on board a flight that landed amid high winds at Dulles International Airport in Virginia on Friday morning.

The FAA Tower at Dulles was briefly evacuated Friday.

In Washington, D.C., federal workers got the day off Friday, as winds gusting up to 70 mph hit the region. "Travel is dangerous," warned the NWS, "and motorists need to be aware of rapidly changing road conditions due to the potential of downed trees and power lines. Pedestrians will face very hazardous conditions, and need to be aware of wind-borne projectiles."

Amtrak cancelled train service Friday along its Northeast Corridor — from Washington, D.C. to Boston — citing "hazardous conditions."

In New Jersey and in New York officials warned of moderate coastal flooding into the weekend.

Mike Eliason / AP

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Meanwhile, in Southern California, the worst of a major storm passed without triggering new debris flows on slopes denuded by summer wildfires.

Up to 30,000 people had been under evacuation orders in foothills of Santa Barbara County, with sheriff's deputies going door to door ordering people to leave. The orders were lifted at 9 a.m. local time Friday. County officials reported minor damage and no damage to utility infrastructure.

Flash flood warnings for the area were also lifted early Friday, the AP reports.

" 'Things are going very well,' Suzanne Grimmesey, a spokeswoman for Santa Barbara County, said shortly before dawn. 'The worst of the storm has passed over.' "

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It's a favorable outcome from "the biggest storm of the season," as Jim Mathews, a meteorologist with the National Weather Service in Sacramento, described it to The Los Angeles Times.

However, parts of the Sierra Nevada Mountains remain under a winter storm warning, with snowfall reaching up to 20 feet in areas, according to the NWS.

Christopher Dean Hopkins and Parth Shah contributed to this story.

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