The polar vortex that is normally located near Hudson Bay, Canada can shift to a position that places it over the Northeast, U.S. The polar vortex is a core of very cold polar air. The density of the cold air causes heights to fall aloft. This produces a closed trough in the upper troposphere. When the polar vortex is overhead, bitter cold air continuously gets recycled over the same general area. The closed trough produces a closed circulation aloft that is cyclonic and mimics a trough aloft that would typically be seen over a mid-latitude cyclone. This can bring bitter cold temperature to the Northeast U.S. When a bitter cold air outbreak is forecast, look for the polar vortex at 300 mb and also analyze 850 mb temperatures at links below: UNISYS 300 mb panels UNISYS 850 mb panels |