Of all of the computer models, only the ECMWF scheme has had a proper handle on what could be the biggest winter storm of 2013 along the East Coast. The model began to show imprints of this disturbance more than a week ago. And the European panels still exhibit what can only be termed a monster system that will greatly impact New England and perhaps a portion of the Mid-Atlantic region. Effects on the New York City metro are still in doubt, largely because of how the gigantic tempest takes shape with respect to its upper air structure, surface and 850MB temperature array, and the possible impacts from the 42 deg F ocean waters east of New Jersey and Long Island. Unlike cities further north, there are still some question marks on just how much snow will occur in NYC.
Phasing between two separate disturbances only yields concentrated heavy snowfall AFTER the merger of the entities is COMPLETE. That event does not happen until around 7 PM ET on Friday evening. With the surface low going vertical with its 500MB component, explosive deepening will yield heavy precipitation plumes that start out liquid or mixed in SW CT, New York City and Long Island in New York state. Since there is a cold "holding" surface anticyclone over Quebec (1038MB), the transition will occur quickly. But by Friday night, most of the higher vertical velocities will be (like the storm itself) along and above the latitude of "The Big Apple". So I would be somewhat surprised to see anyone living south and west of the Interstate 287 belt be involved in the heavy snowfall predicted by earlier runs of the NAM and ECMWF versions. Orography involved with advection of the cold component moving out of the Great Lakes may get some impressive squalls going in northeastern Pennsylvania and northern New Jersey, but at this time it looks like the Trenton NJ and Philadelphia PA metro areas should stay out of meaningful snow accumulations. I say this with crossed fingers.
As the storm undergoes bombogenesis (reaching core pressures of 976MB below Nantucket MA around 12z Saturday morning), the developing snow plumes should expand and intensify. Some forcing moving out of upstate NY will continue past the Hudson River, falling south and east through Connecticut. The gradient between the cyclone and the Canadian ridge complex will be impressive, and winds may reach 60 mph over most of New England, as well as N NJ, NYC and LI NY early Saturday. Snowfall rates will be staggering, aided by thunderstorms that should form in a line rimming the north and west side of the Nor'easter (the clue for cold air convection: check out the extreme 700MB vertical velocities and the 500MB vorticity core). It is entirely possible that more than 2 feet of snow could occur over CT....RI....MA....SE NH....C, S ME from this system. And spikes past 3 feet (think of the visibility with the howling wind blowing the falling and existing snow around...) could occur in and 25 miles either side of an arc from Ledyard CT to Portland ME.
The snow should exit the New York City metro area by the middle of the morning of February 9. But locations such as Hartford CT, Providence RI, Boston MA, Concord NH and Auburn ME will be doing battle with the "Blizzard of 2013" until the wee hours of Sunday. So will much of New Brunswick, as the weakening low center moves north-northeast into nearby Nova Scotia. With a warming trend likely to set in early next week, there will be a whole lot of melting going on. Impacts from this system will involve power loss, closed major highways, street flooding (rain will be coming in two waves next week) and very possibly school closings Monday as communities attempt to dig out from the heavy snow.
See the accompanying slide show for graphics which describe the structure and possible effects of the storm.