The Siberian Express will ride again next week, as frigid air pushes across much of the U.S. with temperatures in some places dropping to as much as 50 degrees Fahrenheit below average for this time of year.

The cold will come courtesy of two main weather features — a wobble in the upper level polar vortex that will pull cold air out of Siberia, Alaska and Canada,

While this will be a headline-grabbing event, with temperatures remaining below zero Fahrenheit for the daytime high across the northern Rockies, parts of the Plains and Midwest, it is not likely to equal or beat the severity of the January 2014 Polar Vortex event.

First, snow cover is unusually sparse across the U.S. right now, and snow is an efficient radiator of heat back out into space. In other words, the presence of a deep snowpack tends to make cold air masses even colder.

Tuesday's high temperature projection by the GFS model, showing highs in the single digits and low teens Fahrenheit. Image: weatherbell analytics

Second, a roaring jet stream at upper levels of the atmosphere, intensified by the difference between the polar air to the north and comparitively mild air to the south, could keep this Arctic blast from overstaying its welcome.

This means that there will be a few truly frigid days to deal with during the middle to end of next week from Des Moines to Minneapolis to Chicago, before temperatures rebound from the ridiculously cold to the merely unusually cold.

Computer model projection for high/low temperatures for the next 15 days in New York City. Image: weatherbell analytics

However, some models are showing that the cold air that had built up in Siberia for weeks as well as Alaska and Alberta will regroup in Canada and push southeast again, affecting the Midwest and Northeast beyond next week. This means it may be a very cold Christmas and New Years for these areas.

Polar vortex is implicated

The much-maligned polar vortex is involved in this upcoming weather whiplash event, in which parts of the U.S. will dramatically cool after the country saw its warmest fall season on record.

The main polar vortex is a circulation of air enveloping a near-permanent area of low pressure that exists in the upper atmosphere, above typical cruising altitudes for commercial jetliners, over the Arctic.

When these winds weaken, as has been happening recently, filaments of the vortex can break off, and meander south into the U.S., Europe and parts of Asia. Last month, parts of the vortex set up shop over Siberia, causing exceptionally cold and snowy conditions there while driving unusually mild air into the Arctic and melting sea ice.

Now the pattern is shifting, with pieces of the vortex spinning across Canada and the U.S.

If you think this week will be #frigid, check out the source region for the air in Minneapolis next Tuesday. #arctic #mnwx pic.twitter.com/Jpjnl1U3Q2 — Tom Niziol (@TomNiziol) December 7, 2016

The Arctic air mass may moderate somewhat as it surges southeast toward the East Coast, where temperatures of 20 to 40 degrees Fahrenheit below average are possible during roughly the Wednesday to Saturday period.

This translates to highs in the teens Fahrenheit in New York and Boston, and lower 20s in Washington, though these forecasts may change as computer models get a better handle on the weather pattern with time.

At most intense, 4855 m at 500-hPa level for manifestation of tropospheric polar vortex anchored over Ontario. Impressive forecast +7d pic.twitter.com/V5aOysDocp — Ryan Maue (@RyanMaue) December 7, 2016

As usual, there is considerable uncertainty with forecasting extreme weather events this far in advance, but the cold snap is shown in multiple computer models, including computer model ensembles that help provide forecasters with an idea of forecast ranges and uncertainty.

This lends some confidence to the likelihood of an Arctic blast, even if the precise details in terms of the severity of the cold are not locked in yet.