30
Day

The coldest air of the season in place across the central U.S. (35°-40° below average) is quickly spreading south and east into the Deep South and the Northeast with only minor modification (weakening) over widespread snowpack which is also still expanding behind 2 distinct winter storms lined up to track from the Rockies to the mid Atlantic coast through the end of this week. NWS Extreme Cold Warnings and Advisories valid today across nearly the entire Eastern half of the U.S. (including the western and central Gulf Coast) are certain to be extended as all models maintain extreme double-digit below average anomalies through the end of this workweek. While this intense level of cold air at the surface can only be slow to moderate through the coming weekend (Feb 22-23) faster pattern change aloft is certain to intensify above average warmth already building across the Desert Southwest (70s-80s) near record levels next week (90s), and spread this warmth east of the Rockies in a progressively weaker form during the final week of February. In this scenario cold temperatures across the Plains from North Dakota to Texas reverse fastest and greatest, to double-digit above average anomalies by Monday, Feb 24. In contrast slower and far less intense warming across the Midwest and East (mainly 3°-6° above average) peaking later next week will also remain briefest and most prone to periodic moderate cooling into early March under lower heights aloft.  Progressively greater forecast divergence separates extended range models with GFS forecasts currently coldest deep into the Midwest and East especially by the 11-15 day period. Unlike prior extended range modeling which attempted to substantially warm all of Canada all latest runs shifted notably colder north of the border, adding confidence to ultimate establishment of a north-south temperature gradient across the U.S. typical of La Niña. Longer range forecasts of both the CFSv2 model and 30-day MWA ensemble are latching onto this as leading to a markedly colder 2^nd week of March featuring winter-like temperatures (highs mainly in the 30s) across the Great Lakes, Ohio Valley, mid Atlantic region, and Northeast strongly suggesting significant delay to the start of spring across the northeast quadrant of the U.S.