WILLIAM BRANGHAM: Welcome to the "News Hour."

A powerful storm battered California, triggering mudslides, severe flooding and multiple evacuations.

At least three people were killed, including a sheriff's deputy.

It's a record-setting Christmas Day for rain in the Golden State, and more is coming tomorrow.

Officials are warning travelers to reconsider holiday travel plans as dangerous conditions may only get worse.

As floodwaters engulf a home in San Bernardino County, a rescue helicopter lands to evacuate the family that's stranded up on the roof.

Tim Needham filmed this incredible scene.

TIM NEEDHAM, San Bernardino Resident: We saw there were a bunch of emergency lights down at the end of the road, and we walked as far as we could without getting swept up in the water, and saw that there were people, that my neighbors were on top of the roof, three people on top of the roof, just sitting there and waiting.

WILLIAM BRANGHAM: Similar scenes played out across Southern California today and yesterday, roads turning treacherous with mud and debris forcing the shutdown of major highways.

On hillsides badly burned by the massive fires earlier this year, a deluge like this can loosen the soil even faster, making conditions even more dangerous.

SHANNON WIDOR, Orange County, California, Public Works: In the canyon areas here, we have very steep terrain, and we have the creek here behind us.

So the burn scar, it doesn't give water the chance to saturate into the ground.

WILLIAM BRANGHAM: Northern parts of the state were also slammed with heavy rains and wind that triggered mudslides in multiple communities, and, in the mountains, huge amounts of snow blanketing the Sierra Nevadas.

In Wrightwood, a ski resort town in the San Bernardino Mountains, officials issued a shelter-in-place warning for residents who didn't evacuate and now must watch as muddy waters course through their town.

WOMAN: There's a little low bridge there.

That's the one that's completely covered, had a car in it, and that's gone now.

WILLIAM BRANGHAM: This colossal downpour triggered by a storm known as an atmospheric river also knocked out power earlier today for nearly 150,000 people.

These conditions prompted California Governor Democrat Gavin Newsom to declare a state of emergency in multiple counties with the National Guard on standby.

As this humid subtropical air from California blows across the country, much of the U.S.

was unseasonably warm on this holiday, with temperatures in some parts of the Midwest and South 15 to 30 degrees warmer than normal, making Christmas for millions feel more like spring.