A pre-Thanksgiving travel nightmare for millions is shaping up as two powerful storm systems blast across the country. One looks to target the Plains, Midwest, Great Lakes and northern New England while a rare “bomb cyclone” crashes ashore on the West Coast. A patchwork of snow and wind alerts stretches continuously from the U.S.-Mexico border to Canada.

Key airport hubs that could see major delays and/or cancellations through Wednesday include Minneapolis, Chicago, Los Angeles, San Francisco and Portland. At Denver International Airport, where heavy snow is occurring, nearly 500 flights have already been canceled.

Strong winds, hefty rain and snow totals and even severe weather are in the offing for large swaths of the western and central Lower 48, where land and air travel alike could be disrupted or even rendered impossible. And that’s not all — a third significant storm looks to brew in the days immediately following the Thanksgiving holiday.

More than a foot of snow has already plastered eastern Colorado since late Monday afternoon. That storm will continue to organize at it treks across Kansas and Nebraska on Tuesday afternoon before targeting the Corn Belt on Tuesday night.

By Wednesday morning, the Great Lakes will be dealing with heavy rain or snow and strong winds as the system bolts toward Canada. It may even skirt northern New England on Thanksgiving Day with powerful winds in its wake.

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To the west, a potent storm is intensifying off the Pacific coast, meeting the criteria of a “bomb cyclone” due to its rapid strengthening. The National Weather Service is calling it an “unprecedented” storm for the southern coast of Oregon and northwestern California, where localized wind gusts could approach 80 mph.

An accompanying storm system will snake its way down the Golden State coast, bringing well-needed rain to Southern California. In the mountains, that water will come down as several feet of snow. Gale-force winds, isolated thunderstorms and coastal flooding are all in the cards as well.

Here’s a region-by-region look at the weather hazards facing the nation:

Eastern Colorado, Plains and Great Lakes

Blizzard and winter storm warnings stretch from northeastern Colorado to the Canadian border north of Minnesota and Michigan’s Upper Peninsula.

Hefty snow has already poured down in eastern Colorado and eastern Wyoming. Interstates 70 and 76 were closed as near-blizzard conditions raged. Some high-altitude locations in Colorado had picked up 30 inches, while 12 to 20 inches were on the ground around Boulder and Fort Collins.

Several more inches could fall in northeastern Colorado on Tuesday morning, but the bulk of the additional snowfall is slated for Nebraska, northwestern Iowa, southern and eastern Minnesota, western and northern Wisconsin and the Upper Peninsula of Michigan, where widespread totals of 6 to 12 inches are forecast, with locally higher amounts possible.

The National Weather Service is forecasting 10 to 15 inches in the Twin Cities. If the bulk of it ends up falling Wednesday, as currently predicted, Minneapolis could wind up with a top-three, one-day November snowfall.

From roughly Des Moines to Madison and to the south and east, the storm is mostly wet — not white.

In Chicago, an inch or so of rain is expected from Tuesday night through late Wednesday. But anyone traveling through O’Hare or Midway airports should plan for possible delays, as strong winds associated with the storm could make it difficult for planes to land. A high-wind watch is in effect for sustained 30 to 40 mph winds with gusts to 60 mph possible Wednesday.

To the south, high wind warnings are already up for much of New Mexico, the Texas Panhandle and adjacent Oklahoma, spots that will see strong southwesterly and southerly winds racing in to fuel the storm to their north. But with relative humidity dropping as low as 15 percent, the stage is set for a pocket of critical fire weather. Red flag warnings encompass areas at risk, and the National Weather Service in Norman, Okla., cautioned that “if fires start, they will spread rapidly.”

Mississippi Valley

The cold front associated with the storm in the Plains and Great Lakes will touch off strong to potentially severe storms over much of the Mississippi Valley on Tuesday afternoon and night. Pockets of damaging winds are the primary concern, with uncertainty over the extent of the tornado risk that will develop.

The National Weather Service has declared an elevated (slight to enhanced) risk zone for severe thunderstorms from northern Louisiana through Missouri and eastern Illinois on Tuesday, an area that includes St. Louis, Little Rock, Memphis and Springfield, Mo.

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West Coast storm

A rare Pacific bomb cyclone is developing off the Oregon coast at the moment, intensifying at a rate twice that needed to classify it as a meteorological bomb. The National Weather Service is calling it a “historic, unprecedented storm” for the areas it will impact. An extremely unusual hurricane-force wind warning is in effect for the ocean waters offshore.

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As the storm rapidly strengthens, its internal air pressure will drop — allowing it to behave in some senses like a vacuum, boosting wind speeds toward its center. On the backside, a “sting jet” will develop, bringing 90 mph-plus wind gusts over the open ocean. If this feature persists, 80 mph winds will be possible near the coast, with “gusts in excess of 100 mph possible at exposed areas and headlands” south of Cape Blanco.

Accompanying that system is an upper-altitude cold pocket that will bring California’s first big winter storm of the season. Two to three feet of snow are possible in the mountains, with “isolated four feet” possible. Snow levels could briefly descend below 2,000 feet in the southern Sierra Nevada.

Meanwhile, heavy rain and flash flooding is possible along the coast and coastal valleys. Flash flood watches are in effect south of Long Beach, Calif., late Tuesday into Thursday.

There’s a chance that Los Angeles could pick up more rain from Wednesday through Friday than the city has had since October 1.

A few low-topped thunderstorms with small hail are even possible and may help to bring stronger wind gusts down to the surface. Coastal flooding is a concern as well.

Another storm in the offing?

Models are consistently developing another storm over the Plains on Friday night, potentially bringing another round of snow and wind for parts of the northern Plains and Upper Midwest on Saturday, along with travel disruptions.