WEATHERAmerica Special Statement, Thursday Afternoon, March 15, 2007

[Larry_Cosgrove]

Intense Storm Set To Lash Eastern Seaboard Over The Next 48-60 Hours; Major Snow, Sleet Threat For Much Of The Northeast With Severe Weather A Concern For The Florida Peninsula

Contrary to popular belief, winter is not yet over. To illustrate this point, consider that a fairly impressive winter storm is organizing which will affect most of Appalachia and the Eastern Seaboard during the next 60 hours or so. A variety of weather elements are involved, not the least of which are chances for heavy sleet and snow, strong winds, a temporary shift to bitter cold, and even a severe thunderstorm threat from the FL Peninsula along the coastline into the VA Capes.

There are two components to the developing cyclone. One is the cold pool and 500MB vorticity maxima over the Deep South, the same system that, with the help of an active subtropical jet stream, has caused heavy rainfall and severe thunderstorms from TX into the Gulf States over the past four days. Another is a digging cA shortwave in the vicinity of the Great Lakes. As the two of these systems collide and phase over the Carolinas early tomorrow, the stage will be set for some wicked conditions, just in time for the St. Patrick's Day weekend.

A convective banding will get underway from FL into NC and VA by late morning Friday. As a negative tilt storm complex organizes. lifting processes (UVV) will expand and advance northward along the Atlantic coast. With a fairly impressive 250MB jet stream nose getting involved from the south and west, potential exists for tornadic supercells along and east of a line from Tarpon Springs FL....Waycross GA....Kingstree SC....Rocky Mount NC....Virginia Beach VA through early tomorrow afternoon. Then convection will fire along and to the north of the developing low center, reaching colder profiles in N VA and MD. Mixed precipitation is likely, turning to snow on Friday night as the disturbance intensifies and passes just east of Cape May NJ.

The tricky part will be the rain/sleet/snow conversion axis. The GFS outlook indicates a sharp wet to frozen transition, roughly approximate to the New Jersey Turnpike late Friday night, while the RGEM and NAM versions suggest a 20 to 30 mile wide corridor of sleet between the rain and snow chambers. Nevertheless, those who see mainly snow (see attached map) will get 8-12" of snow, perhaps more if the system slows down any. By Saturday daybreak, the lowest pressures will be heading across Suffolk County LI NY into W RI. This track implies that any snow or sleet in the eastern half of New England will change to a heavy rain. The strong vertical motion pattern suggests a quick blitz of snow very close to Philadelphia PA and NY, but the Providence RI and Boston MA metro regions are looking at mainly rain. Hartford and New Haven in CT will probably end up as a snow to rain to snow scenario, with some thunder and lightning thrown in for good measure, but escape with minimal accumulation of snow. The "problem zone" with snow and wind created whiteouts will almost certainly be along and 50 miles east of a line from Harrisburg PA....Scranton PA....Albany NY....Trois Rivieres QC (the QC Eastern Townships and the northernmost portion of NB will see the most snow on the Canadian side of the border. As the low undergoes bombogenesis, strong winds will usher in bitter cold air through much of the Great Lakes and Northeast by Saturday afternoon. A well-defined dry slot should end precipitation chances along the Atlantic Coastal Plain following the passage of the storm on St. Patrick's Day.

[Martin]

Nice Discussion.

Already 1.5 inches here so far.

Will have to watch for the heavy convective precip this afternoon for a possible switch to sleet.