The coldest Eastern U.S. arctic air outbreak in over one year this past weekend included the 1^st measureable December snow in NYC observed in several years that is likely to repeat by Christmas Eve. While today is certain to be somewhat warmer as the final arctic airmass of the December series begins to gradually erode, fresh snow across the Northeast will help maintain temperatures colder than models previously forecast through the next several days (below average). At the same time Pacific air flooding the Western two thirds of the U.S. is somewhat cooler than last week’s unseasonable warmth observed west of the Rockies (including several days of record heat in Phoenix), but markedly warmer across the Plains and Midwest featuring double digit above average temperatures. This unseasonably warm central U.S. airmass will eventually spread east of the Appalachians early in the 6-10 day period, but before the period is over (Dec 31) all extended range models initiate the next prolonged cooling trend in the northern Plains. More importantly this faster cold pattern change than models previously forecast includes more intense renewed arctic air transport through Canada, which highly stable 30-day MWA ensemble forecasts continue to focus directly into the Midwest and East in a reinforcing manner during the 2^nd week of January. Similar to the current frigid arctic airmass cresting over the Northeast subsequent temperature moderation in its wake between mid and late January is also likely to proceed slower than models forecast. However, with mid latitude flow exhibiting greater La Niña forcing the next coast to coast warm-up is near certain by late January before Eastern temperatures likely plummet again at some point in February.