30
Day

Another lobe of Canadian air diving into the Northeast late this past weekend is of high confidence to represent the final brief interval of unseasonably cold temperatures and widespread Eastern snow in November.  Today is near certain to represent the coldest day of the next 2-weeks across the Northeast (highs mainly 30s) and northern mid Atlantic region (highs manly 40s), after which unseasonable warmth currently entrenched in the southern Plains (80s-90s between Texas and Oklahoma) expands across the entire Midwest and East in a less intense but sustained manner reversing Northeastern temperatures above average (50s) by the end of of this workweek (Nov 21). At the same time increased precipitation frequency and coverage starting across the Midwest, South, and East (nearly all rain) will  limit milder temperatures to slightly-moderately  above average levels into the 1^st week of December. Modest rain-induced cooling includes Texas starting this workweek (Nov 20-21) marking effective end to summerlike warmth for the rest of the year. In a similar manner widespread precipitation underway across most of the Western U.S. remains devoid of significant cold air, but models direct the 1^st arctic airmass of the season into the Pacific Northwest by day-10 (Nov 25-26) initiating a very cold 11-15 day period across the northwest quadrant of the U.S.  As with all arctic air outbreaks initially directed into the U.S. west of the Rockies progressive airmass modification is certain across the central and Eastern U.S. (especially over below average snowcover) limiting intensity of cooling across the Midwest, South, and East near seasonal temperatures at best through the 1^st week of December. However, that is not the case from early in the 2^nd week of December onward according to consistent 30-day MWA ensemble forecasts which re-establish deeply negative NAO styled Atlantic blocking. This is considered likely to represent prolonged cold pattern change shifting the focus of most December arctic air outbreaks more directly into the Eastern half the U.S. potentially into the start of January, before near sustained below average temperatures can moderate.