el nino is + 4, at sea surface level. it's not that much around it. the atantic is also warmer than normal.
but it's +10 degrees in the north.
that means that the difference in temperatures went from y-x to (y+4 - (x+10)) = y-x + 4 -10 = y-x-6. that makes it harder for a polar vortex to develop. as that +10 inches up even further, the difference comes down even more, and the polar vortex goes away.
it's a very simple argument but it's the basic point that the models forecast - the faster increase in temperatures in the arctic stops the polar vortex from forming. instead, then, what you get is cold air that flops around and incrementally gets eaten by the warmer air. temperature always flows from hot to cold.
when entropy wins, winter loses.
here in southern canada, you still get shorter days (which max out in december, not february) and some amount of cold air will sink but it will have decreasing effects.
meanwhile, in texas, where the effects of the seasons are less, and trump just idiotically cancelled methane restrictions, they will increasingly get no reprieve from the humidity at all. if the polar vortex gets shut down, there's nothing preventing the heat from building. if there is no cold air sinking from canada, the changes in daylight are not enough for it to get cold. you could see cat 5 hurricanes and 100 degree weather in january.