Here’s what’s driving the frigid storm that’s messing up holiday plans across the US

Frigid temperatures are expected to sting two-thirds of the continental US this week as a powerful storm system races eastward. The timing couldn’t be worse, hitting right before the holidays, when many Americans are planning to travel. Those journeys — and even just being outside in some of the hardest-hit regions — may become treacherous as brutal cold blankets the country.

“What better way to kick off the official start of astronomical winter than with numerous winter weather hazards impacting a majority of the Nation,” a National Weather Service (NWS) forecast said early Wednesday. This morning, the NWS updated its forecast to warn of “widespread disruptive and potentially crippling impacts across the central and eastern United States.”

The biggest culprit behind the holiday madness is an extremely cold air mass moving in from the Arctic. That’s ushering in conditions surprisingly similar to the legendary “Great Blizzard of 1978,” experts tell The Verge. Fortunately, forecasters can now issue more accurate warnings much earlier than they could in the ’70s. Hopefully, that’ll give people enough time to prepare and keep themselves safe. This storm system packs a number of punches — from rapidly dropping temperatures to dangerous winds, snow, and ice.

“You won’t see the like of this kind of a storm probably another time in the next 25 or so years,” Jonathan Martin, a professor of atmospheric and oceanic sciences at the University of Wisconsin-Madison, tells The Verge. “It’s really intense, and in some locations, the impacts will be extraordinary.”

Why is the US facing a record-breaking cold air mass? Well, the sun set at the North Pole on September 21st. The Arctic is in the dead of its months-long winter darkness. With no sun to warm the air up, Martin explains, “All that the air can do is cool off because it’s a 24-hour-long nighttime. So you can generate exceptionally cold air masses at this time of year.”

That cold air mass was able a ride south thanks to a buckling jet stream, which is basically a narrow band high up in the atmosphere of strong winds that blow from west to east. “The jet stream essentially is doing what would you could call a roller coaster ride. It’s basically picking up that cold airmass from western parts of Canada and the Arctic and driving it almost due south across the Great Plains and Great Lakes,” Greg Carbin, chief of the Forecast Operations Branch at the NOAA Weather Prediction Center, tells The Verge.

The jet stream pattern we’re seeing now happens to look a lot like it did back in 1978. That year’s “great blizzard” in the Ohio Valley and Great Lakes region stripped hundreds of thousands of homes of power and heat and killed over 70 people. “This once-in-a-lifetime storm will always be the standard by which the severities of all future winter storms to hit this region are judged,” according to the National Weather Service website.

Rapid temperature drops and devastating wind were hallmarks of that storm and are the biggest concern for forecasters now. Across the central High Plains, temperatures have free-fallen some 50 degrees Fahrenheit within a few hours as the leading edge of that cold air mass, the cold front, advances. Yesterday in Laramie, Wyoming, temperatures plummeted from 27 degrees to 3 degrees in only 15 minutes. The quick drop in temperature raises the risk of ice suddenly building up on streets and roadways, particularly in places forecast to get rain before the cold arrives. A couple dozen daily temperature records could be set in the days ahead, according to Carbin.

The sharp temperature contrast between the cold front and the warmer air it meets is also the perfect recipe for an intensifying cyclone with fierce gales. The storm is expected to intensify quickly enough to be considered a “bomb cyclone,” which is when atmospheric pressure in the center of a storm drops at least 24 millibars over 24 hours. A cyclone is another term for a low-pressure system, and lower pressure leads to stronger storms.

Wind gusts with this storm system are forecast to reach over 60 miles per hour. That’s a dangerous combination with even moderate snowfall. Those blizzard conditions could knock out power and make travel impossible ahead of the holiday weekend. And even weaker gales will make it feel even more frigid outside. Wind chills as low as minus 70 degrees Fahrenheit are possible in parts of the Great Plains through the rest of the week. Without taking precautions, exposure to wind chill that bad can cause frostbite in less than five minutes, according to the NWS. More than 30 states face wind chill warnings, watches, and advisories as of today.

“Definitely the scale of the storm itself is much larger than your typical nor’easter or Midwest blizzard,” says Andrea Lopez Lang, an associate professor of atmospheric and environmental sciences at the University at Albany. She’s already expecting scientists to descend upon the dynamics of this cyclone for their research. The conditions surrounding this storm, she says, are “a textbook example of how to get storms to intensify.”