Siberia is the big Northern Hemisphere cold source (for North America and Europe). N Pac (-EPO) and Greenland (-NAO) blocks direct cross polar flow from Siberia into AK and w'rn Canada over the coming weeks, but most of that goes into carving out deep western trough. 1/13 pic.twitter.com/ZHoQJyjaTZ

— Jim Sullivan (@JimSullivan92) December 23, 2021