2:40 PM | **Major pattern change to cold begins tomorrow in the I-95 corridor…next week’s cold shot looks real impressive and there may be a coastal storm to deal with in the Northeast US**
Paul Dorian
Surface-level isobar (lines of equal pressure) pattern associated with pattern-changing cold front (Ohio Valley) and powerful storm system in southern Canada; map courtesy NOAA/WPC, crankyweatherguy twitter
Overview
A major pattern change is going to begin on Wednesday in the Mid-Atlantic region and it will result in an extended period with colder-than-normal temperatures. This initial shot of cold will be followed by a reinforcing cold air mass this weekend and then a significant cold air outbreak is likely next week which may accompanied by a coastal storm. The pattern-changing cold front is now crossing the Ohio Valley and it is trailing a powerful storm just north of Lake Superior.
12Z Euro forecast maps of 500 mb height anomalies (left) and 850 mb temperature anomalies (right) for next Wednesday, December 13th; maps courtesy tropicaltidbits.com
Discussion
This December will be a far cry from the last five years in the I-95 corridor which were unanimously above-normal in Philly, DCA and New York City (see table).
A pattern-changing cold front will usher in an initial blast of cold air for the Mid-Atlantic region on Wednesday and this will just be the first shot of many to come during the month of December. This first shot of colder-than-normal air will head all the way down to the Gulf coast states by the latter part of this week. Ahead of the strong cold front, it has turned mild in the I-95 corridor and showers are breaking out just to the west of here. There may even be a period of steadier rain early tonight as the front pushes through the region and colder air will become quite noticeable on Wednesday with stiff NW winds.
This initial shot of cold air will feature an intensifying trough of low pressure in the eastern US with plenty of waves of energy rotating through and each system will attempt to generate low pressure near the east coast. As a result, the threat for some snow in the I-95 corridor will persist from later this week into the upcoming weekend. Odds currently favor much of this activity to stay just to the east of the immediate I-95 corridor, but still needs to be closely monitored as this can shift to the north and west as event time approaches.
Looking ahead, another significant cold air outbreak is destined to arrive by the middle of next in the eastern US and it will feature an energetic upper-level low that could spawn the formation of a coastal storm in the Tuesday/Wednesday time frame. Next week's cold shot is likely to feature even colder air relative-to-normal than these first couple of outbreaks.
Stay tuned.
Meteorologist Paul Dorian
Vencore, Inc.
vencoreweather.com