(This story has been updated.)
Frigid air will grip an unusually large portion of the Lower 48 states in just over a week’s time. The cold is predicted to consume almost the entire nation, from the Pacific Northwest to the Southeast, sparing only Florida.
While some parts of the country are forecast to experience temperatures 30 to 50 degrees colder than normal, the cold snap will be most remarkable for the amount of real estate it is predicted to cover.
Brian Brettschneider, a climatologist based in Alaska, noted Thursday that the National Weather Service’s six- to 10-day temperature outlook (below) projected the nation’s largest area with high confidence (90 percent probability) of below-normal temperatures in 15 years of issuing such outlooks.
The cold will take the better part of next week to reach the East Coast, first arriving in the Pacific Northwest and the Northern Rockies this weekend.
Some of the coldest air, relative to average, will focus on the region from the Pacific Northwest to the Northern Plains early to the middle of next week. Cliff Mass, an atmospheric science professor who blogs about Seattle weather, wrote that the cold snap could be “far colder than we have seen in many years. ”
Before the cold air reaches the eastern half of the nation, abnormally warm air (30 to 35 degrees above average) will first surge northward between Monday and Wednesday.
On Tuesday, high temperatures could rise to 60 degrees as far north as southern New England.
But Ryan Maue, a meteorologist with WeatherBell Analytics, said an elongated jet stream will “allow chunks or blobs” of the frigid air to work their way east. “It’s clear by Day 10 [Jan. 8] that there is a very strong cold signal (10 degrees or colder anomalies across entire U.S. coast to coast) except for South Florida, which has enjoyed record heat during December,” he said.
Matt Rogers, a meteorologist with Commodity Weather Group, said it takes a rare jet stream to deliver cold air to both coasts simultaneously. “Typical jet stream wavelengths are too narrow to allow cold outbreaks to reach coast-to-coast nearly simultaneously,” he said. “The width of this upper level trough pattern is impressively large.”
The jet stream configuration will result from twin areas of high pressure over Alaska and Greenland, which, together, will force the flow of air southward over North America — from the Arctic toward the Gulf of Mexico.
The nation also experienced such coast-to-coast cold air during the winter of 2013-2014. But that cold was more intense than what is predicted for next week. “Unlike the polar vortex event of January 2014, the main center of the polar vortex is kept over the Hudson Bay and unable to penetrate the Midwest,” Maue said.
This kind of pattern happens more frequently during La Niña events like we’re seeing now, according to Michael Ventrice, a meteorologist with the Weather Company. But he cautioned that it would not be a “permanent fixture” of the winter. He concluded: “This winter will be a winter of extremes, with violent swings between Arctic cold and much-above-average temperatures for the eastern two-thirds.”