The article explained that there are two roughly equal drivers: (1) Water is a better heat reserve than land, and winds tend to blow eastwards, so Europe gets air warmed by the sea and the US east coat gets colder air that's come from the land. (2) The joint effect of the altitude of the Rockies and the angular rotation of the earth mean that air currents are southeast over the Rockies and then northeast, so arctic air gets pulled down and then pushed back up over the US east coast.