This is how our forecast Polar Vortex Breakdown - Sudden Stratospheric Warming - plays out over the next 2 weeks ~20 miles aloft, as per the GFS model. This top and bottom comparison is a good visual on how breakdown occurs. Notice on top how the frigid Polar Vortex (L) is large and in charge. On the bottom panel - 2 weeks later - warm high pressure expands & impinges on and displaces the cold vortex circulation. This can “unleash” frigid Arctic air trapped in the once strong vortex circulation.