Christmas 2019 Polar Vortex shrinkage North American side; RECORD WARMING follows, how did this happen?

~From Chicago USA: https://chicago.suntimes.com/news/2019/12/28/21039824/warm-christmas-chicago-climate-change-great-lakes

~To even Moscow: https://www.theguardian.com/world/2019/dec/29/moscow-resorts-to-fake-snow-in-warmest-december-since-1886

~The root cause,  of course, was a warmer Arctic,  with likewise much smaller size Polar Vortex

     We go strait to the root cause:

  The size of the Polar Vortex on December 25-26  may be defined at 248 K isotherm threshold at level 600 mb.   As you can see the vortex is spectacularly small and covers even less ground over North America.    It has 3 vortices,  all quite cold, as per latest observations, the warmer the Arctic gets the more prone for small but very cold PV vortices.  Obviously there is no or very little circulation originating from the entire sub Arctic towards North America and western Eurasia.  How did it get this way?

      This was from a build up of unusual Arctic circulation pattern  covered here at EH2r since late November.     Namely by cyclones heading North from the West side of Greenland. 
Here was one of the last significant warm air blitz:

The recent Polar Vortex was not always shrunken,  December 19 to 25 action demonstrates one of the latest warm cyclones bringing up air from the West coast of Greenland,  all the way to Northern Siberia by way of the North Pole.  The culprit here is the Western Canadian Arctic CTNP (Cold Temperature North Pole),  a vortice of the vortices within the Polar Vortex.  Like a hurricane eye,  this vortice has been reorganizing according to the massive warm advection,  it could only reposition itself westwards,  within a much warmed,  hence shrunken PV as seen on my first NOAA daily composite animation presented above.    This shape of the Polar Vortex took place after several Baffin Bay cyclones headed Northwards likewise.  The sum total is a shrunken PV,  reorganized in similar way as before,  with a CTNP always prone in injecting more warm air in addition to the usual North Pole warming route,  from the North Atlantic.   Of particular interest is the weather of Japan, which will likely vary greatly from rainy warm days to Siberian cold in the matter of a few hours,   I have yet seen something which will break the current circulation pattern,  it seems quite stable,  but thinner sea ice may eventually reshape PV dynamics within 2 weeks. WD December 29,  2019