Polar air and a powerful winter storm put millions under winter alerts this holiday week

By Aya Elamroussi, CNN

For millions of Americans across a large swath of the country, the holiday week is beginning with unrelenting below-freezing temperatures made even more miserable by heavy snow expected Tuesday and Wednesday in several central and northwestern states.

A developing ‘bomb cyclone’ has prompted alerts from Washington state to Maryland that cover over 50 million people, according to the National Weather Service, and that number is expected to grow over the coming days.

A ‘bomb cyclone’ is a term used by meteorologists to describe a rapidly strengthening storm. Specifically, it means a drop of 24 millibars (a term used to measure atmospheric pressure), in 24 hours. These storms frequently occur with winter nor’easters, but in this case, the bomb cyclone is expected to occur in the Plains. That’s because of the extreme temperature difference between the warm and moist air in advance of the storm and the extreme Arctic air mass moving in from Canada.

This weather phenomenon is expected to be the pressure equivalent of a category 2 hurricane as it reaches the Great Lakes, with the weather service now calling the strength of the low a “once-in-a-generation” event.

More than 40 million people are under wind chill alerts across much of the central and northwestern US, including in places slammed with blizzard conditions by a separate storm system last week. Parts of Alabama and Tennessee are also under a wind chill watch as the “feel like” temperatures are expected to plummet below zero.

On Tuesday, the sprawling weather system is delivering dangerously cold temperatures and snow to Montana, North Dakota, South Dakota and most of Minnesota, where high temperatures will remain below zero, according to forecasters at the NWS.

The air feels so cold, frostbite on exposed skin can occur in under 10 minutes in most of the impacted areas, and some isolated locations in under five minutes, forecasters warn.

“In addition to the brutally cold temperatures, dangerous wind chill values of 35 to 55 degrees below zero are possible into the end of the week across these areas,” the Weather Prediction Center said Monday.

Wind chill advisories are in place for Sioux, South Dakota, and Fargo, North Dakota, Tuesday, when the dangers of frostbite are settling in. Wind chill, which indicates what the wind feels like, will be as low as 40 degrees below zero, and in Wyoming on Wednesday night could hit a staggering 70 degrees below zero.

“Starting tonight, the worst of the arctic air mass will reach our area, bringing dangerous temperatures and wind chills. Slippery roads will continue with additional accumulating snow expected Tuesday afternoon through Wednesday morning,” the weather service office in Glasgow, Montana, said Monday evening.

Drastic temperature drops are coming. In Denver, for example, the temperature will be 50 degrees at noon on Wednesday but is expected to drop to 12 below by daybreak on Thursday. Similarly, New Yorkers will enjoy 60-degree weather on Friday in Manhattan and then see a temperature of 24 degrees as a high on Christmas Eve.

Snowfall has already begun in Seattle, which is under a winter storm warning Tuesday. The storm will move east into portions of Idaho Tuesday morning and then spread out across northern and central Montana later in the afternoon.

As the storm moves east this week, it stands to make holiday travel difficult, if not dangerous, in many places, with forecasters urging people to be prepared to make changes.

In Minnesota, the weather service in the Twin Cities implored residents to be cautious of the “potentially dangerous week of weather,” with the worst of the effects in the Midwest beginning Wednesday.

“The bottom line is travel will be very dangerous and could be LIFE-THREATENING later this week so be prepared to alter travel plans now!” the local weather service office said.

Many local governments in the affected areas have opened warming centers in an attempt to provide relief to those who need it.

What’s ahead Christmas week

Overall, most of the US is expected to see abnormally cold temperatures this week. In fact, more than 80% of the country, excluding Hawaii and Alaska, are forecast to see below-freezing temperatures.

In Montana, Helena and Missoula are under winter storm warnings beginning Tuesday, and Billings is under a wind chill advisory through noon Friday.

The storm is also expected to intensify as it approaches the Midwest, where the greatest impacts are forecast. Snow will begin in the region Wednesday and last through much of the Christmas weekend.

In parts of central Minnesota, several inches of fluffy snow are expected Wednesday, followed by high winds, creating the potential for blizzard conditions. A blizzard is defined as having winds of at least 35 mph along with falling or blowing snow which reduces visibility to a quarter-mile or less, for at least three hours.

“By Thursday, wind gusts of 40-50 mph appear likely. With the fluffy snow in place, blizzard conditions are highly likely area wide, even in areas that typically aren’t favored for whiteout conditions,” the weather service said.

Chicago is forecast to be one of the hardest hit cities, where a winter storm watch is in effect starting Thursday night through Friday evening. With blizzard conditions likely, holiday travel could grind to a halt for many seeking to celebrate with family and loved ones.

The city could pick up 6 to 8 inches of snow from Thursday morning through late Friday night and when combined with 55 mph winds, the weather will bring travel to a stand still. The blizzard conditions could close O’Hare airport during the peak of the storm and will likely cause the cancellations of hundreds of flights in Chicago alone.

“Rapidly deteriorating conditions by late Thursday afternoon, with dangerous blizzard conditions appearing increasingly likely Thursday night into Friday,” said the weather service office in Chicago, home not only to one of the nation’s busiest airports but also long-distance train depots.

South bracing for unseasonably cold temps

Meanwhile, even southern cities unaccustomed to wintry conditions will get a brittle taste of it this holiday season, with Austin, Houston, Atlanta, and even Orlando at risk of seeing temperatures below freezing beginning midweek.

In Texas, the weather service made it a point to reassure residents this week’s unusually cold temperatures are not expected to affect the state as severely as last year’s brutal winter storms, when millions of people lost power during a weeklong extreme weather event in February 2021.

However, water pipes will be at risk of bursting, the weather service said. A wind chill watch for Amarillo, Texas, is in effect from Wednesday night through Friday afternoon.

“Outdoor pipes will be at risk due to well below freezing temps and windy conditions late this week,” the weather service in Fort Worth said. “Make sure to cover pipes and let faucets drip!”

Mississippi is urging residents to start bracing for what could be an extremely cold couple of days, the state’s emergency management agency said in a Facebook post Tuesday morning.

“Dangerous, cold temperatures are expected this week for most of the state. Start prepping NOW,” the post said. “Wrap pipes and keep a preparedness kit in your car with extra blankets. Remember the Four P’s of Winter Weather Preparedness. People, Pets, Pipes, and Plants!”

Much of the state is under a hard freeze watch, according to the weather service. Subfreezing temperatures are expected.

“A prolonged period of subfreezing temperatures may cause pipes to burst. Bitterly cold temperatures and wind chills will result in hypothermia and become life-threatening to those with prolonged exposure or without access to adequate warmth,” the weather service said.

In a post Monday, state emergency management officials reminded residents to seal windows and doors, insulate pipes and test smoke alarms.

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CNN’s Robert Shackelford, Jennifer Gray and Michelle Watson contributed to this report.