State highway officials warned that all roads could become treacherous overnight Wednesday, with temperatures expected to drop to the mid-30s in Baltimore and colder outside the city.

"People who are out tonight need to be really careful because whatever is on the ground is going to freeze," state highway spokeswoman Sandra Dobson said Wednesday.

At Baltimore-Washington International Thurgood Marshall Airport, the weather caused delays of an hour and a half or more to destinations in the Northeast, according to the Federal Aviation Administration. Thirty-three flights to and from the airport had been canceled as of 4 p.m., according to FlightAware.com.

Around the nation, airlines had canceled more than 1,800 flights, according to the airline monitoring website Flightstats.com.

A tornado watch had been in effect for part of the day Wednesday in eastern North Carolina and northeastern South Carolina. By Thursday, the storm could dump 12 to 18 inches of snow from the lower Great Lakes to northern New England, the National Weather Service said.

On Christmas Day alone, the weather service received 34 reports of tornadoes in eastern Texas, Alabama, Louisiana and Mississippi, Vaccaro said.

In Baltimore, the mix of precipitation was a confusing and cold combination that prompted people waiting at bus stops to don puffy winter jackets to insulate themselves and carry umbrellas to protect themselves from the rain.

The weather was cold and wet enough to make framing contractor Steve Kirby "hate it" but not bad enough to keep him and his crew at home instead of hoisting long planks of wood through a second-story rowhouse window for a rehabilitation project near Patterson Park.

"Your hands get numb," said Kirby, who works for Soperbuilt Woodworks of Baltimore.

But some took advantage of the snow. There was enough on the ground Wednesday morning to allow Kyoko Duke, 8, her brother Savon Elder, 10, and their father, LaMarre Elder, 29, to build a snowman outside their door on South Ellwood Avenue in Highlandtown.

The kids' stepmother had pitched them the idea while flakes fell before 11 a.m., and the entire family joined in, grabbing all the snow they could find on the sidewalks and across the street at Patterson Park. For half an hour, Savon and Kyoko gave up playing with the new Xbox and Monster High School House doll set to create a body of giant snowballs that they adorned with a carrot and red scarf and topped with a blue beret.

But by noon, the "wintry mix" was more sleet than snow and the kids were back inside and in their pajamas watching the animated movie "Monsters Vs Aliens" on TV.

"The snow's kind of wettish," Savon said.

Sled tracks ran up and down the hill outside Greenwood Mansion on the Baltimore County Board of Education grounds in Towson. But no sledders could be found Wednesday afternoon. The weather had shifted from snow to sleet to rain, driving them all back inside.

Forecasters expect one more storm system to move from the Gulf Coast to the Mid-Atlantic and Northeast over the weekend, but the details are proving difficult to predict, according to the weather service's Hydrometeorological Prediction Center in College Park. The storm could move more quickly than previous systems, though precise snowfall predictions depend on its ultimate track, strength and timing, according to a forecast discussion posted Wednesday morning.

The weather service's local forecast office is calling for a chance of more ice, rain and snow from Saturday morning through early Sunday.

Baltimore Sun Media Group reporters Kevin Rector and Bryna Zumer and Tribune newspapers contributed to this article.

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