This will be one of those classic cold air damming situations in which cold isbacked up against the Appalachians and it just sits there while mild, moist airattacks from the southwest. Being much lighter, the mild air rises up and overthe low-level cold air to create the perfect setup for ice.Because the warm layer is well above the surface, it can't snow but sleet orfreezing rain cdo occur. The worst case is when the rain falls all the way tothe ground in liquid form, then freezes to a glaze of ice on everything. That'swhen travel becomes the most hazardous, plus the extra weight of the ice canbring down tree branches and power lines.

The ice storm will begin in western North Carolina and southwestern VirginiaThursday night, then will spread northward to interior Pennsylvania and upstateNew York Christmas Day.

Story By AccuWeather.com Senior Meteorologist John Kocet.