The wind chill on Mount Washington in New Hampshire crashed to at least 108 degrees below zero Friday night.

ORLANDO, Fla. – The northern tier of the country has been in the grasp of Arctic air for the last week. The core of the potentially record-breaking cold air will settle right into the Nation’s heartland over the weekend. The second is the stratospheric polar vortex which forms in the winter and resides over the polar regions way up in the stratosphere. When the stratospheric polar vortex is weak, the tropospheric polar vortex or polar jet stream also tends to weaken, allowing for Arctic air to spill into the Lower-48. (NOAA)The Arctic oscillation tracks the stability of the polar vortex.