The polar vortex and associated cold 500mb temperatures really sloshed around from December 1-15, really dumping the cold and snow on us. Then we had some varied weather patterns, including a ridge on Christmas Day that split the cold anomalies east, west, and north. High values of Greenland blocking (west negative NAO blocking) came along with the polar vortex motions in the first half of the month.
https://great-lakes-salsite.web.app/Dec_2025_500mb_loop.html