JAN
25
https://easternmassweather.blogspot.com/2019/01/arctic-cold-and-snow-to-accompany-polar.html
Arctic Cold and Snow to Accompany Polar Vortex Visit Mid Week
Significant Winter Storm Possible Tuesday Night into Wednesday
In an effort to spare our readers the sensationalism surrounding the media driven hype pertaining to the "polar vortex", we would like to preface this narrative by cautioning that a pool of very low atmospheric heights accompanied by brutal arctic air will be entering the country through the northern plains next week. This is the polar vortex.
What the polar vortex is not: The polar vortex is not a major storm in and of itself. It is not some meteorological monster that guarantees impending meteorological doom for the entire country. Our sincerest apologies to CNN, and Fox News. What the polar vortex is: The polar vortex is simply a "vortex" of very low atmospheric heights that has been dislodged from the arctic, as heights began building in in that region. Its presence in the US does increase the likelihood of potentially record breaking cold, and a major winter storm should a piece of it interact with energy from the southern branch of the set stream.
At the same time that this polar vortex descends into the mid latitudes of the US, some of this arctic energy will attempt to "phase" into and invigorate a bundle of energy in the southern branch of the jet stream to create a storm on the east coast. Here is the depiction on todays 12z European model:
Compared to last nights 00z European run, two trends are apparent:
1: The arctic energy more aggressively phases into the souther stream, resulting in a more proficient coastal cyclogenesis. next week.
2: The ridge on the west coast, referred to as the PNA ridge, is slightly more stout and placed more to the east, closer to the west coast, where as the ridge on the image below is not quite as pronounced and is displaced a bit to the west, off of the coast.
The first trend is important because it lends credence to the notion that at least some of the arctic energy associated with the polar vortex will feed into out nascent system along the east coast. Because otherwise, we are left with merely some snow showers in advance of very cold air.
The 12z European ensemble suite also bolsters confidence in the more phased scenario.
Now that we have gained some clarity with regard to the first notable trend of today, lets revisit the second trend and the implications of more phasing relative to this. 2: The ridge on the west coast, referred to as the PNA ridge, is slightly more stout and placed more to the east, closer to the west coast, where as the ridge on the image below is not quite as pronounced and is displaced a bit to the west, off of the coast. Thus far this season, it has been exceedingly difficult to for much of southern New England to experience a significant snowfall in the absence of precipitation type issues. This is because there has been no downstream blocking in the vicinity of Greenland and the Davis straight (-NAO), thus there has been nothing to prevent the storm from tracking close enough to us to advect warmer air in, especially in the mid levels. This is precisely what took place in Sunday's storm, as arctic high pressure prevented much warmer air from moving in at the surface, except for southeastern Mass, however nothing stopped the mid levels from warming and changing snowfall to sleet and some freezing rain. This remains a distinct possibility Tuesday night into Wednesday, as while we do have an arctic high pressure to provide resistance to warm air advection at the surface, a more phased system will tend to track the mid level lows either over our area, or even to the west since there exists no downstream blocking. However there is a slight chance for major snowfall across eastern sections of the area should the PNA ridge out west continue to trend more to the west and more amplified, while we also see just the right degree of phasing as not to pull the mid level lows further to the west, closer to the parent polar vortex. Regardless, since the system will likely be intensifying explosively as it traverses the area, there is at least a short term blizzard risk at play.
This latter scenario, while unlikely, remains a distinct possibility.
Currently, the 12z GEM and GFS models act as voices of descent, since they reflect both a less pronounced southern stream system and degree of acrostic phasing, thus they produce more meager and seaward east coast cyclogenesis.
GFS:
GEM:
Quite frankly, since we are now only about 120 hours out from modeled phasing, it is exceedingly unlikely that the operational ECMWF has been incorrectly trending towards the more phased solution that has been supported by its ensemble suite for days. Thus the notion of minimal phasing modeled by the GFS and GEM are bing dismissed. In fact, it is probably more likely the eastern New England "threads the needle and receives in outright blizzard. But neither scenario is supported at at this juncture.
