With travelers' advisories posted from coast to coast, Christmas Day dawned snowy in the Northeast, frigid in the Midwest and parts of the South and foggy in the West, where the dense mist that has led to seven deaths lifted yesterday after forcing cancellation of hundreds of flights into Seattle and Reno, Nev., and stranding thousands of passengers.

In the nation's capital, the white Christmas forecast earlier failed to materialize. The cold air moving east stalled over the Appalachian Mountains, and by the time it got here early yesterday morning the rain was ending.

National Airport reported an unspirited whitening of less than one-tenth of an inch of snow.

Washington area temperatures fell about a degree every two hours yesterday, from 34 degrees at midnight to 24 degrees at 6 p.m.. the National Weather Service said. Water pipes froze, cracked and leaked.

Today's weather is expected to be partly cloudy and colder, getting down to about 10 degrees downtown and 5 degrees in the outer suburbs. With winds of 10 to 15 miles per hour, wind chill is expected to be about 10 below in the city and 25 below farther out.

Though winds might not be at their harshest, "it will be very cold," said weather service forecaster Edwin Danaher. Tomorrow is expected to be warmer here, with highs in the mid- to upper 30s.

It was another story in n southern California, where temperatures soared into the 80s, and Christmas surfboards rode the waves.

That was little consolation to Florida citrus and vegetable growers, however. They were looking past Christmas Day's eclectic weather to the subfreezing weather that was expected in northern Florida this morning. The freeze could threaten the state's $2.5 billion agriculture industry, already devastated by past freezes and disease.

A blast of frigid air blowing south from Canada was expected to cause subfreezing weather in northern Florida and near-freezing temperatures in central Florida.

"This is going to be a situation we have to watch," said Wayne Colin of the National Weather Service in Miami. "It doesn't look like it'll be as cold as the '83 freeze that killed all the citrus crops. But it'll still be plenty cold."

On the West Coast, the fog that hovered over areas of the Puget Sound for nine days is gone -- but only temporarily, according to Bob Herzog, spokesman for the National Weather Service in Seattle.

"It all depends on where you live and what hilltop you look down from or what valley you see," Herzog said.

Elsewhere, a winter storm dumped heavy snow on parts of eastern New York and Vermont, and then moved into Canada. As much as 13 inches of snow was reported in the northern Vermont mountains and as much as 7 inches was measured at Stillwater, N.Y.

"I see my stream, and the water's coming down, and it's snowing right now. It's beautiful," said John Miller at the Toll Road Motor Inn in Bennington, Vt. "It's rather prosaic. What else can you say about snow other than it's beautiful?"

As much as four inches of snow fell in the northern mountains of North Carolina. Atlanta recorded a trace of snow -- only the seventh time since weather records began that snow has fallen in Atlanta on Christmas Day. The last time was 1970.

Snow also fell in Birmingham, Ala., but melted off as the sun came out.

The mercury plunged to a 18 below zero at Houghton Lake, Mich., the coldest Christmas Day since 1921.

"There is no truth to the rumor that Santa had to come to the weather office this morning to get a jump start for his sleigh," one National Weather Service forecaster joked.

It also hit 18 below at Hibbing, Minn., and the wind chill in Chicago was estimated at 42 below zero.

Hundreds of people jammed Salvation Army shelters to escape the Windy City's bitter cold.

"We've had to turn away a few families," admitted Ronny Holloway, an assistant supervisor at the Salvation Army's North Side emergency lodge. "We've got 98 families here now."

The West Coast's thick fog was a factor when a light plane crashed into a shopping mall in Concord, Calif., Monday night, killing four persons and injuring 77, authorities said.

The heavy mist also contributed to the death of a woman who fell down an embankment during a multicar crash near Livermore, Calif., Saturday. Freezing fog caused a 13-vehicle pileup that killed two persons on Rte. I-5 last Thursday near Grants Pass, Ore.

Oregon officials warned that heavy fog and icy roads made driving in the interior valleys in the southwestern part of the state extremely dangerous.

California officials issued travel warnings for the central valley through Christmas Day, noting that fog probably would reduce visibility to less than one mile in some areas.

Some areas in the Sacramento and San Joaquin valleys of California have not seen the sun since Dec. 11, the National Weather Service said.

Snow, freezing rain and sleet fell across New England, New York, the Ohio Valley and the mid-Atlantic Coast. Lake-effect snow was reported in the Great Lakes region, and heavy snow warnings were posted for northeast Ohio and northwest Pennsylvania.

Light snow lingered in the central Plains and spread across western Oklahoma.

Subzero temperatures were common from the Dakotas south to Missouri and the lower Ohio Valley.

Bakersfield, Calif., tied a 20-year-old record for most consecutive days of dense fog with 12 straight days of the thick ground-hugging soup, and the National Weather Service said no end is in sight.