~The coldest zone at start of winter since 2012 was 2016
~Yes, the warmest year in history twinned with greatest El-Nino
A continuance of warmer global temperatures creates smaller but much colder Polar Vortex internal vortices.
The way to show this is by taking the ENSO cloud seeding theory, which means there are more clouds during El-Ninos worldwide, either in summer or winter. More clouds in Arctic winter definitely turns it warmer, so was the great El-Nino of 1998 the turning point for Arctic sea ice extent , the beginning of its significant declining trend. The feedback of yearly ever increasing lesser sea ice areas should not be underestimated, must remind: long in duration La-Nina's are destructive for sea ice, especially since 1999, sea ice also plays a major role in world wide climate at either Poles.
Note, declining sea ice mangles ENSO's global circulation role year by year as sea ice volume and extent vanishes, it gives quite the interesting start of winter GC look, note a couple of days at the dawn of winter are very significant if looked holistically, a wide expanse of planet Earth is in effect an average compared with identical same day periods, long term averaging dilutes the GC outlines :
Consider the extent of Polar Vortex within the orange zone (the jet stream line), astounding as you may notice, 600 mb temperatures are very close to the weighted temperatures of the entire troposphere, but the coldest temperatures measured at beginning of winter were mostly during the warmest years, especially 2016, the warmest year. Warmest years December 13-14's had much smaller jet stream outline (-25 C, 248 Kelvin border), colder years had naturally a vaster expanse of colder air but, this is a big but, mainly much warmer internal vortices. Warmer years had mainly top of sea ice great warming incursions, Cold Temperature North Poles (CTNP) were closer to the North Pole during colder years.
The easy question is: what causes this? Refraction observations of vertical sun disk expansions or compressions have confirmed this phenomena. During the last two springs, 2019 and 18, the Canadian Arctic Archipelago Vortice (english language needs adjust to the times) was found radically colder but smaller. Dark season long term observations rendered tentative conclusions, the Cold Temperatures North Poles have largely migrated Southwards, away from lesser and thinner sea ice, snow on ground species have tended to be more of the "wet" snow type, more sublimation and mostly there seems to be a tendency for more stable but smaller cloud free zones, which tend to be in a deep freeze feedback loop.
What about 2019-20 winter: