Last weekend's storm, which dumped 10 inches of snow in both St. Louis and Washington, may have been one of the first indicators of the shift to harsher winter conditions.

"I think the snowstorm this weekend was related to the vortex split," said Judah Cohen, a researcher at Atmospheric and Environmental Research in Boston, and polar vortex expert. "I think we're seeing the impacts already."

After the vortex fractures, it can fundamentally alter the flow in the atmosphere. Steering winds that blow from west to east - transporting mild air from the Pacific Ocean over the continental U.S. - shift to more north and south. Arctic air can more readily be drawn into the North America and Europe.

"The first-order impact [of a vortex split] is that you slow the west to east flow and add more of a north-south component," Cohen said. "There's a much greater exchange of arctic air that's moving south."

A blast of a bitter Arctic air is forecast to plunge into the eastern U.S. late this week and this weekend, the coldest of the winter so far in some areas - another possible sign of the vortex disruption.