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Fierce ‘bomb cyclone’ to disrupt holiday travel, unleash Arctic outbreak

The storm could bring blizzard conditions, ‘life-threatening’ cold, extreme wind chills and travel headaches for large parts of the Lower 48 states

A large storm system is expected to move through the United States starting on Dec. 20, bringing heavy snow and freezing temperatures to much of the country. (Video: John Farrell/The Washington Post)
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A massive storm system is set to snarl holiday travel and bring an onslaught of wintry weather to millions across the Plains, Great Lakes, Ohio Valley, Northeast and even interior Mid-Atlantic. The developing cyclone will deliver heavy snow and blizzard conditions to some and downpours to others between Wednesday and Friday night, all coming at a time of year when more than 110 million Americans are expected to take to the roads and air.

The potential exists for serious travel disruptions at major airport hubs in the Midwest and Great Lakes, including Chicago’s O’Hare International, where heavy snow and howling winds are expected — with the worst conditions late Thursday into Friday. The combination of snow and wind will bring visibility down to near zero at times.

Travel could “become extremely dangerous and life-threatening, particularly in light of the bitterly cold temperatures during the height of the storm,” wrote the National Weather Service office serving Chicago.

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Nearly 50 million Americans are under winter storm warnings, watches and advisories. On Tuesday afternoon, the first blizzard warnings were issued for western and southern Minnesota and are expected to be extended to the east and south. The anticipated storm system will explosively strengthen, at a rate sufficient to qualify it as a “bomb cyclone” — which is the most intense breed of mid-latitude storms.

“In summary, this is still looking to develop as a high end, life-threatening event,” wrote the Weather Service office serving Minneapolis.

The Weather Service office serving Buffalo is calling it a “once in a generation” storm system.

Airports all across the eastern U.S. could suffer cascading delays and cancellations due to strong winds surrounding the system, which will sprawl close to 1,000 miles across. That could lead to impacts far and wide, from Minneapolis and Milwaukee to Boston and Washington, D.C. The strong winds could lead to power outages in locations that are also experiencing dangerously low temperatures.

The storm will drag a historically cold December air mass — sourced from Siberia — over much of the Lower 48 between late Wednesday and late Friday, sending temperatures plunging some 30 to 50 degrees below average. Readings in the teens could slosh all the way to the Gulf of Mexico, with a dangerous flash freeze turning wet roadways into sheets of ice in some areas.

More than 50 million people are also under wind chill alerts, from the Rockies to the nation’s midsection. Projected wind chills on Friday morning include: 2 degrees in Houston; minus-7 in Dallas; minus-14 in Memphis; minus-32 in Kansas City, Mo.; and minus-45 in Sioux Falls, S.D.

“Dangerously cold wind chills, as low as 50 below zero” are expected in the Dakotas, wrote the National Weather Service. “Stranded motorists will face the threat of frostbite, hypothermia and even life-threatening exposure.”

“We can not emphasize enough - the #cold air and wind chill forecast tomorrow (Wed) night thru Thursday feature some of the most extreme values you will ever see!” wrote the Weather Service office serving Cheyenne, which is forecasting wind chills as low as minus-70 in eastern Wyoming.

The frigid air will bleed all the way to the Eastern Seaboard on Friday, setting the stage for the coldest Christmas since 1989 in many spots.

Dangerous Central U.S. blizzard likely

On Tuesday morning, a weather disturbance was draped over British Columbia, Alberta and Saskatchewan. It will intensify and consolidate into a bowling ball-shaped zone of low pressure at high altitudes, which will dive south over the Northern Plains, Corn Belt and Missouri Valley between Wednesday night and Friday. That will help brew a potent zone of low pressure nearer the ground that will swiftly strengthen, becoming a “bomb cyclone.”

The cyclone will first form over eastern Colorado on Wednesday night, making it to Memphis by noontime Thursday before beginning to rapidly intensify. By Friday morning, it will be near Detroit. That’s when it will dramatically strengthen en route to Canada via the Great Lakes. The strength of this low-pressure zone will be “off the charts” for the Lower Great Lakes in December, according to the Weather Service office in Buffalo.

On the western side of the storm, moisture wrapping around the low and falling into cold air will deposit a swath of heavy snow, with jackpot totals possible exceeding 12 inches. It’s unclear where the maximum will fall, but it’s looking like Wisconsin and the Upper Peninsula of Michigan could be in the double digits. A broad 6 to 10 inches is likely along the shores of Lake Michigan, including in Chicago, with a widespread 3 to 6 across most of the remainder of the Upper Midwest, Corn Belt and eastern Northern Plains.

Here are the forecasts for 10 cities in the path of Christmas week blizzard

Across much of the Great Lakes, the heaviest snowfall and worst conditions are expected between late Thursday afternoon and Friday night. Conditions could gradually improve on Saturday, although winds could still blow the fallen snow around, reducing visibility.

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Snow will break out over the central Plains on Wednesday night into Thursday; as the system strengthens, the snow will become more intense and expansive in coverage into Thursday afternoon, at which point it will be snowing moderately to heavily in Chicago and perhaps all the way down to Nashville.

Around this time, winds will pick up markedly, with widespread gusts of 35 to 50 mph common. That will lead to blizzard or near-blizzard conditions across most of the North Central U.S. and western Great Lakes as dangerously cold air pours into the region behind the storm’s cold front.

Even after the main slug of moisture passes into early Friday, wraparound moisture in the “comma head” of the cyclone will keep light to moderate snows going over Lake Michigan, and especially the eastern lakeshore.

The snow will eventually pivot into the Midwest and northern Ohio Valley before working into the Northeast as rain at first, since temperatures there will be warmer. However, in western Pennsylvania and New York, the rain should change to wind-whipped snow before ending, causing hazardous conditions on Friday and Friday night. Even locations farther east, toward the Interstate 95 corridor, could see rain change to a very brief period of snow as the storm’s Arctic front comes through Friday. With rapidly falling temperatures, that could lead to slick roads.

Although the storm will lift into Canada by Christmas Eve, strong winds circulating around it will generate areas of heavy lake-effect snow on the shores downwind of the Great Lakes into Christmas Day — including around Buffalo

Interior Mid-Atlantic wintry weather on Thursday

Outside of the main blizzard impact zone, a second area of concerning winter weather could come to manifest on Thursday. That will occur ahead of the main low-pressure system as moisture rides up the Appalachians on Thursday. Subfreezing air entrenched in the mountains will take a little while to scour out, so initial precipitation will come down as snow and eventually freezing rain.

Winter storm watches are in effect in the Alleghenies of western Maryland, eastern West Virginia and adjacent western Virginia. That’s where 4 to 6 inches of snow, along with up to a quarter of an inch of ice, are likely. That could impact travel on Interstates 68 and 81 Thursday morning through the day.

Why flight delays could abound

The sheer size of this storm, which will stretch more than 1,000 miles across, is impressive in and of itself. Juxtaposed against a strong Arctic high-pressure system to the west, however, the resulting contrast will be noteworthy. That extreme change in air pressure with distance will make for strong winds essentially over the eastern half of the Lower 48 on Thursday and into Friday. Gusts of 40 mph will be common, with some areas — especially near the Great Lakes — seeing gusts over 50 mph. Tree damage and power outages are probable in areas where it will be dangerously cold.

Where strong crosswinds intersect runways, flight delays will be frequent. For flights that manage to take off, turbulence will make for an uncomfortable ride. This is especially true late Thursday into Friday.

A flash freeze

Meanwhile, bitter cold temperatures are already pooling over the northern Plains, heralding an even more bone-chilling air mass set to crash south over the U.S. in the next 24 to 48 hours. Temperatures could drop as much as — or even more than — 40 degrees, plummeting to levels rivaling the cold air outbreak of 1989.

In the Texas Panhandle, this front will be a true “Blue Norther.” Readings will fall from the mid to upper 40s to the single digits in a matter of five or six hours Wednesday night.

Houston will go from the mid to upper 60s on Thursday afternoon to the lower 20s by Friday morning, with wind chills in the single digits.

Thereafter, the flash freeze front will reach the East Coast, with highs in the 40s and 50s on Friday replaced by lows in the teens by nightfall. Some models even suggest a 30-degree temperature drop in spots in three hours, which would challenge record temperature swings along the Interstate 95 corridor. Any roads in areas that are wet could turn icy.

Major storm to soak D.C. area before a frigid Christmas weekend

How cold it will get

After the coldest air invades, it should stick around for 48 to 72 hours. The biting chill will blast into Denver on Wednesday night, dropping temperatures from 40 degrees to zero in just a matter of hours. By Thursday morning, it will be near minus-10 with wind chills around minus-30.

“Life Threatening Cold Arrives Late Wednesday,” tweeted the Weather Service office serving Denver. “We promise that’s not an exaggeration. This is likely to be the coldest day in 32 years in Denver so many people have not experienced a cold snap like this.”

St. Louis, which will see highs in the mid-30s on Thursday along with some snow, will fall to minus-4 degrees on Thursday night. By Friday, highs will hover around 6 degrees, with lows around zero. Teens are likely for highs on Saturday.

Chicago will be in the single digits from Thursday night through Saturday. Kansas City will dip to minus-8 on Thursday night, and highs probably won’t make it above 4 or 5 degrees on Friday.

Lows in the minus-20s and minus-30s will be common across the Dakotas and Montana, and some places won’t make it above minus-10 degrees for several days in a row. Wind chills will range between minus-40 and minus-55 degrees.

Particularly impressive with this episode is how far south the cold air will blast. Virtually everyone along the Gulf Coast from Galveston to Tampa, including in New Orleans, Gulfport, Miss., and Mobile, Ala., will see lows around freezing on Friday night. That will result in “Arctic sea smoke” over the Gulf, or a rare type of fog resembling steam that forms when cold air blows over warmer water.

Toward the East Coast, temperatures will be 10 to 25 degrees below normal both Christmas Eve and Christmas Day. From Washington to Boston, highs should remain below freezing with lows in the teens.

Much of Florida, except for the far southern portion, will dip into the 30s or lower on Saturday night.