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4 Inches or more (4-8” area) --- on the eastern side; Blacksburg VA, northeast to Allentown PA, Springfield MA, Gloucester MA, and out, to the southeast of that line there will be a few inches of accumulating snow to begin and some ice, however precipitation should go to all rain. On the western side, Blacksburg VA, to Pineville WV, then take that directly north to Cleveland.
8 Inches or more (8-12” area) --- on the eastern side, Union WV, northeast to Harrisburg PA, Pittsfield MA, Portland ME, and out. On the western side, Union WV to Johnstown PA, then northeast to Rochester NY. Local amounts up to a foot will be possible within this area.
In-between the 4 and 8 inch areas respectively, there will be problems with significant freezing rain in the piedmont of VA, up through PA, and into the Litchfield hills of CT after a good dose of snow. This could be a big ticket icing event for a few reasons;
1) The GFS never Gets H85 temps above +3C across the area in question, so therefore as precipitation falls into the sub-freezing layers closer to the surface, not as much warming will take place in the layers closer to the surface IF temps aloft were say +3C to +5C or greater.
2) Snow cover --- the snow pack across the northeast remains intact which would imply that the low level arctic air will be harder to scour out, as compared to what it would be if no snow pack was in place. This can frequently make the difference between a major icing event and heavy rainfall.
3) since temperatures have been so brutally cold lately, even if boundary layers temps should get above freezing for a time, ice accumulation on not only trees and power lines will still be possible, but road surfaces and especially raised structures such as bridges and overpasses as well. Even in spite of what may be marginal boundary layer temps.
Since there is NO Greenland block / –NAO, and NO 50/50 low in position, the surface high pressure center is allowed to slide off to the east, causing southeast winds to develop along the coast, changing any mixed precipitation over to a cold rain.
Thus, the major cities will see a snow to ice then rain event with modest accumulations. And w/o a rapidly deepening surface low, it’s highly unlikely that moisture will be able to wrap around into the cold air, setting the state for decent backlash snows across the big cities. Once the column does cool sufficiently to allow for all snow, the best moisture should already have moves off to the northeast.
With 1000-500mb thicknesses of about 540; and marginal temps, snow/liquid ratios will probably run close to 10:1 across much of the northeast. It is a bit too early to tell with any certainty if we will have the best UVM and RH coinciding with the layers favorable for maximized snow growth. This can be worked out more tomorrow.
ETA soundings at MPO indicated strong instability and a good CSI and convective instability signals with elevated CAPE showing up as well. TT indices were approaching 50 at 60hrs, with dry adiabatic lapse rates of near 7.00 C/km, in addition to rather impressive theta-e drops with height evident in cross-section.
http://weather.admin.niu.edu/chaser/tempgif/26973.TXT
Thus it is possible as the strong UVM moves over the region, CSI is released and P-type becomes a big problem, since the depth and strength of the warm layer is not all that impressive. So the potential exists for violent swings back and forth in precipitation type across the Poconos, Lehigh valley, northwest NJ and much of the central and lower Susquehanna valley, where soundings are close to freezing through a deep layer.
Also ---- a note of the late week possibilities. IF, IF, IF the system early this week which we just discussed closes off as it moves northeast toward Newfoundland, and becomes the new 50/50 low, then not only do we have the potential to see the NAO go negative once again as the wavelengths sharpen and blocking re-develops over the top, but it would force the s/w coming into the southwest this week to take more of a suppressed track at a lower latitude, hence making for a more wintry scenario for the northeast, portions of the mid-Atlantic and new England.
