Snow cover whiplash hits the U.S., with a warm up coming next

• The quick reversal came courtesy of a severe polar vortex-related cold snap that sent temperatures plunging into the minus-40s in Montana at times.
• It also spawned coast-to-coast storms, which knocked power out for millions.
• Some of the snow fell in areas not typically accustomed to it: Nashville saw 7.6 inches for the month, most of it in one day. Because of the vagaries of storm tracks, this was more than New York City saw for the whole month.
• Portland, Oregon, experienced a deadly ice storm that cut power to some neighborhoods for days.

The intrigue: The upcoming weather pattern features a return of a flow of air coming across the Pacific Ocean, and a relatively flat jet stream pattern across the Lower 48 states.

• This should flood the country with milder than average temperatures for this time of year.

• Such a pattern, which also dominated December, is frequently seen during El Niño years such as this one.

What's next: The cold and snow are likely to ease significantly through early February, with some signs of a potential return thereafter.

• But the thaw in the meantime could yield temperatures of 20°F to 30°F above average for this time of year across Canada and much of the Central and Eastern U.S., which will help to slowly melt much of the snow that has fallen away from mountainous areas.

Go deeper: Snow drought finally ends along I-95 corridor