the storm, Sandy, that triggered the headline wasn't unusual in the historic record; the intensity of the storm was amplified by cold arctic air brought in by the Jet Stream a factor that was ignored because warm is the default bias; (drtimball.com)
This allows the lower pressure and very cold arctic air mass to expand further south, chilling everything well down to Scotland. (dotearth.blogs.nytimes.com)
Depending on how far east winter storm tracks travel up the east coast, the battle line between cold arctic air masses to the west and warm Atlantic air to the east causes significant temperature changes. (landscapesandcycles.net)