A powerful storm threatened to bury sections of the Southwest and Great Plains under a blanket of heavy snow Monday, blitzing holiday travelers with blizzard conditions two days before the start of winter.

Warnings forecasting snowfalls of up to 18 inches stretched across the region as the storm barreled through New Mexico headed into the Texas and Oklahoma Panhandles and parts of Kansas and Colorado. In southern Colorado, blizzard conditions were expected to drop between 8 and 16 inches of snow.

In New Mexico, Los Alamos National Laboratory and a number of schools shut down early Monday, and Interstate 25 between Las Vegas and Wagon Mound was closed due to ice and zero visibility. Two other highways in the northern part of the state were closed because of blizzard conditions that were expected to drop up to 15 inches of snow.

The storm hit the Oklahoma Panhandle about 8 a.m., and Vicki Roberts, the owner of the Black Mesa Bed and Breakfast in Kenton, said about 1.5 inches of snow had accumulated outside her place an hour later.

"It's a blizzard. I can't even see the mesa," Roberts said as she peered from the window of her establishment at the foot of Black Mesa, which at 4,973 feet is the highest point in Oklahoma. Forecasts called for the area to get up to 16 inches before the storm moves out Tuesday.

State officials in Kansas were preparing for a similar onslaught in the southwest part of the state, where snow and winds of up to 45 mph were expected to cut visibility to near zero and push snow into high drifts that could block roads when the storm arrives late Monday.

"We are preparing," said Kansas Department of Transportation spokesman Steve Swartz. "We've had a few storms in the northwest, but we are fully stocked with sand and salt in all our regions. We're in good shape."

Travel on major interstates in the region was risky. In addition to problems on I-25, treacherous snow and ice were likely to create problems for drivers on Interstate 35 in Oklahoma, Kansas and Texas, Interstate 40 in New Mexico and Interstate 70 across central Kansas. Motorists were urged to check road conditions before beginning any long journeys.

The storm follows a surprisingly mild Sunday across the region. In the Oklahoma Panhandle, residents enjoyed relatively balmy 60-degree temperatures. That changed quickly, and Roberts said Monday morning that she expected to be stuck inside at least through Wednesday if a blizzard was as bad as forecast.

"I have a mail route and I'm not going. You just don't get out in this," Roberts said. "We'll be socked in here. If we lose power we'll just read a book in front of the fireplace."

There were no guests at her inn, so she wasn't worried about them being stuck.

Kansas still had temperatures in the upper 40s on Monday, and thunderstorms moved across the state. Conditions were expected to deteriorate as the day progressed and temperatures fell. Snow was expected to start in the western part of the state overnight.

The Oklahoma Department of Transportation said Sunday that crews would work around the clock to keep roads clear, and that they have about 130,000 tons of a salt and sand mixture at their disposal.

The precipitation also could help ease a drought that has plagued Texas for more than year.

"You're not going to find too many people who have to put in winter wheat in this area complaining," said Tabatha Seymore, observing program leader for the National Weather Service in Amarillo, Texas. "It's just wonderful to have this moisture to sit on top of the crop and melt. It's fantastic for them."

Amarillo had rain Monday morning, and snow was supposed to start in the afternoon with several inches of accumulation by Tuesday morning.

Long haul truck driver Frank Pringle stopped at a Love's Travel Stop in Amarillo but said he intended to go as far west as road conditions would allow Monday. His biggest worry was with four-wheel-drive cars because "they will shoot past you and cut you off and you have to hit your brakes. And hitting brakes in the snow is not a good thing."

Clayton, N.M., Police Chief Scott Julian said his town is expecting more than a foot of snow. He was worried drivers passing through town to Colorado or Texas might decide to take their chances with the storm only to find that "they get 10 miles out of town, they can't see in front of them, and they get stranded out there."

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Associated Press writers Jeri Clausing in Albuquerue, N.M.; Tim Talley and Rochelle Hines in Oklahoma City; Tim Raths in Washington; Maria Sudekum Fisher in Kansas City, Mo.; and John Milburn in Topeka, Kan., contributed to this story.