In the days leading up to Christmas - one of the busiest travel times of the year - two extreme, disruptive and dangerous weather systems will affect large parts of the Lower 48 states in the US: a very intense storm that will produce blinding snow, heavy rain and howling winds, and an associated outbreak of exceptionally cold air.
The large, powerful storm is set to explosively develop in the Midwest and Great Lakes late this week, unleashing heavy snow and strong winds - and the potential for blizzard conditions in some areas.
Possibly qualifying as a "bomb cyclone" because of its projected rapid strengthening, the storm could bring extreme impacts from snow and wind from the Plains to the interior Northeast between Thursday and Christmas Eve, seriously affecting several major population centers including Kansas City, St. Louis, Des Moines, Chicago, Milwaukee and Buffalo.
While not everyone will see heavy snow this week, few areas outside California and the Southwest United States will escape what the National Weather Service is describing as "a massive surge of arctic air."
Exceptionally cold and windy air will be drawn southeastward from Canada by this potent storm. The cold will seep into Texas - and eventually Florida. Houston could see temperatures in the teens and wind chills near zero Friday morning. On Thursday, subzero temperatures may stretch from Denver to Minneapolis with temperatures 40 to 50 degrees below normal from Montana to the Texas Panhandle.
In some places, this will be the coldest December weather since at least 1989. By the second half of the week, much of the northern Plains, Upper Midwest and Great Lakes will have subzero temperatures - even for highs - with wind chills as low as minus-55 near the Canadian border.
A potentially paralyzing snowstorm
Along the southward-diving Arctic cold front, a very intense storm system will develop. It will tap into jet stream energy, quickly ballooning into a major mid-latitude cyclone.
The counterclockwise-spinning storm system will drag a strip of warmth up the Eastern Seaboard, leading to mostly rain, but cold air crashing south on its backside will support a swath of heavy snow combined with punishing winds between the Upper Midwest and Great Lakes.
The combination of snow and wind will lead to whiteout conditions and impossible travel in some areas. Power outages are an additional concern, particularly considering the extremely cold temperatures predicted.
In its forecast discussion Monday, the National Weather Service office serving the Chicago warned of "rapidly deteriorating conditions by late Thursday afternoon, with dangerous blizzard conditions appearing increasingly likely Thursday night into Friday." It advised anyone with travel plans at that time to "begin to consider alternate arrangements."
Other cities in the region which could be seriously affected include Des Moines, Madison, Wis., Milwaukee, Indianapolis, Detroit and perhaps Cleveland and Buffalo.
The storm will begin to organize over the Ozarks or Oklahoma on Thursday, and then quickly intensify on Thursday night as it shifts toward the Great Lakes.
Weather models have been inconsistent in their depictions of where the storm's track will go; shifts of just 100 miles could mean the difference between a high-impact Chicago blizzard and a mix of wind-whipped rain and snow.
As the storm organizes Thursday morning, a strip of wind-driven snow will sweep across Kansas and Nebraska, with snow likely breaking out over the Upper Midwest and the Great Lakes as the day wears on. Farther east, rain will affect the Eastern Seaboard along the cold front, although snow and ice are possible when the precipitation begins in the Appalachians where cold air remains entrenched.
Through the day on Friday, heavy snow and wind will blast portions of the Upper Midwest and Great Lakes, although it's too early to predict which areas will be hardest hit. Meanwhile, heavy rain will plow northeast into New England and perhaps flip to snow before ending Friday afternoon and night.
Even in areas unaffected by heavy snow, the storm will be a major wind producer, posing a problem for air travel over large parts of the eastern US - especially by Friday.
It's important to note that uncertainty exists with regards to the track of the storm system, which will have enormous bearings on how much precipitation falls and where the rain-snow line sets up. Regardless, confidence is growing in a jackpot zone of at least 12 to 18 inches of snow, which will coincide with strong winds to yield visibilities below a quarter mile or whiteout conditions.
A bitter Arctic outbreak
Cold air is already oozing out of Canada across the northern Intermountain West and northern Plains, with temperatures set to drop at least 40 degrees below average. Wind chill watches, warnings and advisories blanket the Dakotas, most of Montana, parts of Wyoming and Colorado and even western fringes of the Corn Belt.
The alerts herald the arrival of an even more significant deep freeze that will plunge the Plains into an air mass more typical of northern Alaska. When the Arctic front arrives at any particular location, temperatures will drop suddenly and winds will rapidly strengthen.
"Dangerous to life-threatening wind chills as low as 55 below zero [are] possible," wrote the National Weather Service in Bismarck. "The dangerously cold wind chills could cause frostbite on exposed skin in as little as 5 minutes. Hypothermia could develop shortly thereafter."
Across the Dakotas, the coldest temperatures will be observed between Wednesday and Friday, with highs barely poking above minus-10 and lows in the minus-20 to minus-30 range. Billings, Mont., is predicted to have a high of minus-16 on Wednesday; that would match the record coldest maximum for the day set back in 1990.
In Minneapolis, Wednesday and Thursday could both feature highs around zero, with lows of minus-5 to minus-7.
Denver is under a wind chill watch for Wednesday night through Friday morning for wind chills flirting with minus-30. The Mile High City is expecting a very sudden drop in temperature. On Wednesday afternoon, the high is expect to reach 40 degrees; eight hours later, at midnight, it's projected to be near zero. Thursday's high temperature probably won't eclipse zero and the low both Wednesday and Thursday night is expected to be around minus-12.
The frigid air will be far-reaching. By Thursday night, the leading edge of the cold will blast through Little Rock and Dallas, and by early Friday, it will surge to the Gulf Coast.
Little Rock could have a low of 8 degrees on Thursday night, shy of the 2 degree record set in 1989. Dallas is forecast to plunge to 9 degrees, which misses the record of 3 degrees. In St. Louis, a low of zero is likely Thursday night. Memphis may fall down to 5 degrees.
Even New Orleans may only see a high of 37 degrees on Friday, which is just a few degrees above a record low maximum for the date. Once again, the cold air outbreak of 1989 claims many records.
There's a growing chance that cities like New Orleans, Mobile, Ala., Panama City, Lake Charles, La., and perhaps even Pensacola, Fla., may be treated to a rare display of "Arctic sea smoke" on Friday morning. Resembling steam, the rare type of fog occurs when bitterly-cold air blows over milder waters.
Particularly problematic will be the abrupt arrival of the cold air, which could bring a flash freeze all the way down to the Gulf Coast. In areas with standing water left on untreated roadways, that could translate to a rapid icing concern. The sudden cold could also burst pipes.
The core of the cold will reach Chicago and surrounding areas of the Great Lakes Friday into Saturday. The Weather Service predicts "[d]angerous bitter cold with wind chills -20F and lower Friday night into Christmas Day (Sunday) regardless of the track of the late week storm system."
The cold will reach the East Coast Friday night when temperatures will drop sharply. For both Christmas Day and Christmas Eve, temperatures will be about 10 to 25 degrees below normal and the coldest since 1989 in many locations.
Even Florida will feel the chill. Lows are forecast to dip into the 30s in Tampa and Orlando Friday and Saturday nights.