This will be one of those classic cold air damming situations in which cold air is backed up against the Appalachians and just sits there, while mild, moist air attacks from the southwest. Being much lighter, mild air rises up and over the low-level cold air to create the perfect setup for ice.

Because the warm layer exists, it can't snow, but sleet or freezing rain do occur. The worst case is when rain falls all the way to the ground in liquid form, then freezes to a glaze of ice on everything. That's when travel becomes the most hazardous, and the extra weight of the ice can bring down tree branches and power lines.

The ice storm will begin in western North Carolina and southwestern Virginia Thursday night, then spread northward to interior Pennsylvania and upstate New York Christmas Day. Approximate starting times of the ice event are shown here.

We also show the region where we feel the icing will be most pronounced.

Story By Senior Meteorologist John Kocet.