Three rounds of cold Arctic air from a shifting polar vortex are expected to plunge much of the central and eastern U.S. into a cold snap in the coming weeks, meteorologists say. The first wave of the triple whammy of winter weather is happening this week.

How colder air interacts with a developing storm will determine if and where a band of snow or a mix forms from the Appalachians to New England, with rain farther south and travel delays possible late week.