January 4, 2008: Sunday Evening Prospectus

A pattern reconfiguration is set to transpire on the planetary scale as the position of the troughs and ridges shifts to bring ridging back to the Eastern Pacific and Western North America, and troughing rebuilds to the Eastern half of the United States.  All the while, the atmosphere will retain below normal heights across most of Central and Southern Canada, with the deepest negative anomalies developing over the Eastern United States.  The result will be frequent visits from anomalously cold air, and the potential for winter weather when strong shortwaves can intensify quickly enough to develop closed circulations and tap Atlantic moisture. That's in the medium to long range - in the more immediate future, a quick-moving low brings some interest early Monday, and a more meaningful storm appears on tap for Tuesday night and Wednesday.

A quick warm front/cold front progression associated with an open surface wave is moving east, with current radar imagery showing the convective clusters moving east ahead of a prefrontal trough.  These clusters are fueled by weak cyclonic vorticity advection in the mid-levels, and the best dynamic lift pushes through Western and Northern New England Monday morning.  This keeps the best chance of early morning precipitation from CT (esp. Western) through Western MA, then east along and/or north of the Route 2 corridor of Northern MA.  Temperatures throughout the column are below freezing in the North Country, where light snow will fall.  850 temperatures are above zero south of this, however, while surface temperatures will be below freezing owing to the combination of an antecedent cold airmass and a light gradient wind limiting the potential for surface warm advection.  This ends up meaning light freezing rain for Central/Western New England on Monday morning, then the precip will end as dynamic lift diminishes, and more importantly, cold advection begins.

The shot of cold that follows is the result of a strengthening gradient flow between the large low northeast of the St. Lawrence, and the high building northeast across the Ohio Valley.  This high moves over New England on Tuesday, and though it will initially hold the cold by increasing the barometric pressure and subsidence while cold air is in place following the antecedent cold advection, the overall motion of this high doesn't really favor deep cold holding on, considering it's approaching from the southwest, then weakening as it moves over and northeast of New England. 

This leaves the next southern stream charged shortwave a bit short-handed when it comes to deep cold air to crank out snow later Tuesday night into Wednesday.  There's also plenty of indication that the northern and southern streams have trouble phasing until later in the game, meaning the moisture feed of deepest moisture and therefore highest precipitation amounts stay a bit east of New England.  Still, even if this doesn't change in the days to come, there will be a surge of warm and moist advection into the cold dome for a swath of accumulating snow from south to north Tuesday night.  There's concern for a change to freezing rain and sleet for the interior, and this will depend heavily on the strength and track of the low - the ECMWF is quicker to intensify the system and takes it very close to the coastline, which would favor developing a north and northeast wind through the interior to hold the cold for icing, but at this point is largely alone in such a scenario.  Nonetheless, winter weather will greet many on Wednesday morning, and the North Country will likely see significant snow as the low winds up and the mid-level front slows over the North Country.

Another shot of cold comes Thursday and Friday with the gradient between departing low and approaching high.  At the same time, a strong shortwave rotates through the base of the trough, acting as a fast-moving clipper that will intensify dramatically south of New England late Thursday.  At this point, it would appear development occurs too far south to affect New England, but this is subject to the evolution of the longwave pattern, especially in relation to the Wednesday storm's intensity and track.

A similar strong shortwave will be tracked for next weekend, but even greater uncertainty exists as to the longwave pattern, and therefore any potential track of this system.

Matt

Comments

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