Heavy snow across the West, winter storms in the Midwest, and cold up and down the East Coast and across Canada have set up ski country for one of the best Christmas vacation weeks in memory.

OnTheSnow's regional editors have summarized conditions across North America which, in a word, are excellent.

That seems to be a combination of La Nina, which pumps moisture-laden air from the Pacific onto the continent, and thinner Arctic sea ice, which allows a flow of warm air north and bitter air south.

White Christmas? No problem. Much of the West is celebrating record snows and ski areas being 100 percent open long before the holidays. A parade of snowstorms has kept the snow base mounting at levels more commensurate with late January rather than December.

So, who's been getting the big snows? Mammoth Mountain, several Tahoe resorts, and Jackson Hole crossed the 200-inch mark by Dec. 20 for total snowfall this winter.

Most resorts in the Far West, except for SoCal, got set up well for the holidays with a monster record-breaking snowstorm last weekend that dumped 5-to-15 feet of snow in four days.

Early snow piled into the Northern Rockies, making Jackson Hole, Grand Targhee, Big Sky, and Whitefish Mountain delighted to have the best early season skiing of the last several decades.

Pacific Northwest ski areas from Alaska's Alyeska Resort to Oregon's Mt. Bachelor bumped easily into full operation this winter with some ski areas, such as Sun Valley seeing the best conditions in a decade.

Holiday skiers and snowboarders will find plentiful snow at Canadian coastal resorts such as Whistler Blackcomb and inland resorts such as Sun Peaks, Lake Louise, and Sunshine Village.

Colorado Gem resorts are experiencing the best conditions in a handful of years. Many have already reached 150-plus-inch-snowfall totals. Northern and southern resorts are receiving generous snowfall from the recent storms hammering the state. Wolf Creek and Silverton are getting buried, while Arapahoe Basin, Monarch, and Sunlight are all relishing incredible powder conditions.

Records continue to fall at Colorado resorts, as the holiday season is in full swing. It's a very snowy Christmas in Steamboat with 3-to-5 feet of snow the week before the holiday. Snow fell hard in the southwest, with over 2 feet at Wolf Creek, Crested Butte, and Silverton.

 "We'll likely see the early season momentum continue with resorts being active over the holidays due in part to the great snow conditions and abundant events," said Melanie Mills who heads up Colorado Ski Country USA.

Heavy snow is expected to keep falling on Colorado's resorts into Christmas day, ensuring the slopes are well covered for the long holiday season.

La Nina has had her way with the Mountain Southwest so far this season. In the north, the Wasatch Mountains of Utah got it early and often, allowing several areas to open earlier than expected and promising full coverage for the holiday period.

Southern Utah mountains shared in some of that largesse. Farther south, New Mexico resorts have had rely on snowmaking until a decent storm came through last week. Arizona remains unseasonably dry. More snow was forecast for Christmas.

The Northeast has not enjoyed the heavy snow that has fallen elsewhere in the U.S., but a decade of investment in high-efficiency snowmaking technology has paid off big time in this season's three-plus-weeks stretch of perfect snowmaking weather. More terrain is open early across this region than has been in years. Persistent light snow the past few days has added freshies to the mix, coating manmade cover with a frosting of cold, natural powder.

A series of snowstorms crossing the Great Lakes and cold air dumping in behind the systems has the Midwest dressed in a mantle of white for the holidays.  Ski resorts across the region are expecting big crowds over the holiday period.  From the Black Hills of South Dakota to northeast Ohio and as far south as St. Louis, ski areas are in good shape with a combination of natural and manmade snow.  Most are fully open.

Cold air also has settled over the Mid Atlantic resorts, allowing early December openings across that region, and lots of terrain for Christmas.

Regional editors Brett Buckles, Andy Dennison, Becky Lomax, Shannon Luthy, and Mike Terrell contributed to this report.

More informatin: OnTheSnow Snow Reports.