Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.

Six people have died and thousands were without power as a brutal winter storm continued to sweep across the United States and brought snow and ice to a swath of the Southeast, while strong winds and heavy rained battered parts of the West.

Vehicle crashes in Georgia and Kentucky on Saturday killed two people, officials said. A Maine man died in a Friday crash with a snowplow and another person died in a Kentucky crash on Thursday, officials said. A tree buffeted by high winds in Oregon fell on an 8-year-old on Tuesday, killing her.

And a woman was killed at a golf course in San Ramon, California, after she was struck by a tree that had fallen due to heavy winds Saturday, fire officials told NBC Bay Area.

Parts of northern California and Nevada were filling sandbags as an "atmospheric river" threatened to dump very heavy rains and cause flooding Sunday. More than half of California was under flash flood watches.

In California's Bay Area, residents were hunkering down for expected heavy rains. Flash flood watches were in place for the San Francisco and Monterey Bay region through Sunday night and officials set up sand bag locations.

"We're giving them a shovel and the sand and showing them how to fill them up,'' Jason Hoppin, a Santa Cruz County spokesman, told NBC Bay Area. "We haven't seen rain like this in a long time.''

High winds and heavy rain were reported throughout parts of northern California on Sunday, Frank Giannasca, a senior meteorologist at the Weather Channel, told NBC News. The weather conditions had caused trees to topple over he added, as the loose soil caused tree roots to weaken, he added.

Rain and snow was also expected to spread up through the Northwest and parts of the Mountain states, Giannasca said.

The storm was forecast to bring rain late Sunday night into Los Angeles and spread into the Plains, bringing a wintry mix to North Dakota and Minnesota by Monday.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

In Connecticut, a stretch of a major highway was closed for hours Saturday after a 21-car pileup and other crashes, state police said. No serious injuries were reported.

The ice and freezing overnight temperatures evoked memories of past winter storms in the South, like one in 2014 that stranded thousands of drivers on paralyzed interstates around Atlanta and elsewhere.

"If I tell you anything it would be stay home," North Carolina Gov. Roy Cooper said Saturday. “Do not go out and drive on the roads unless you absolutely have to."

As traffic creeps past on the New Jersey Turnpike, drivers work on cars stuck in the snow Saturday, Jan. 7, 2017, near New Brunswick, N.J. Mel Evans / AP

The Federal Aviation Administration ordered a temporary ground stop at Philadelphia’s airport Saturday due to ice and snow, and major delays were reported at New York City-area airports.

A little more than 5 ½ inches of snow was recorded at New York’s John F. Kennedy Airport and LaGuardia saw just over 4 ½ inches of snow by Saturday evening, the National Weather Service said.

It was treacherous travel in North Carolina, with the state Highway Patrol reporting 260 wrecks during the storm. In the Charlotte-Mecklenburg area, there were 46 crashes with injuries from 10 p.m. Friday into around noon Saturday, EMS said.

Across the state more than 9,000 customers were without power as of Saturday afternoon, down from 16,000, the state Department of Public Safety said.

In Virginia, state troopers responded to 527 crashes and helped 686 stuck drivers by Saturday evening. “Give ‘em a rest. Stay home!” Virginia State Police said in a Twitter message to drivers.

Boston’s mayor warned earlier Saturday of up to a foot of snow; by just after 8 p.m. nearly 6 inches was recorded in the northeast section of the city, the weather service said, although the city of Weymouth to the southeast did reach a foot by then.

"It does wrap up as we go into Sunday, but leaves behind bitterly cold air,” according to Weather Channel meteorologist Danielle Banks.

Low temperatures of 5 to 10 degrees — and with a wind chill near zero — had been forecast for Richmond, Virginia, overnight.

Lows of 15 degrees were forecast for New York City on Sunday; a low of 14 degrees were forecast for Philadelphia; and 15 degree low was eyed for Washington, D.C. In Raleigh, North Carolina, a high of 27 degrees during the day and a low of just 2 degrees at night was forecast.

Out West, another storm prompted winter storm warnings and advisories for a swath from eastern Washington and much of Oregon to Idaho, northern Nevada and northwestern Utah.

Reno, Nevada, prepared for floods and states of emergency were declared in Washoe, Douglas, Storey and Lyon counties, NBC affiliate KRNV reported.

Yosemite National Park closed access to Yosemite Valley in anticipation of expected flooding of the Merced River Sunday. The Generals Highway into Sequoia National Park was closed due to rock slides and flooding, cutting off access to the big trees.

A forecast of dangerous snow and ice in Oregon prompted a home Portland Trailblazers basketball game and a University of Portland men's college basketball game against Gonzaga to be postponed.

People pick up sandbags from the Department of Public Works Operation Yard in preparation of the incoming storm in San Francisco on Jan. 7, 2017. STEPHEN LAM / Reuters

More than 100 flights into or out of Portland's airport Sunday were canceled, the airport said Saturday night. In Eugene in southern Oregon, 4 1/2 inches of snow fell Saturday, the National Weather Service said.