First of all, look at the precip blossoming:
The precip shield should continue to expand and backbuild as the surface low gets it’s act together just off the southeast coast:
Snow is being reported over sections of northern MD, VA, and south central PA. It was actually snowing here in Nazareth overnight and the temperature has dropped to 35 degrees currently, and is snowing as far south as the higher elevations of the Quakertown area. It’s raining at ABE right now – the power of ELEVATION! The rain will transition over to snow in areas where it isn’t snowing now from north to south through the day especially as the storm gets cranking. Nothing’s really changed in my thinking from the overnight final call:
Latest Mesoscale discussion and map from Norman, OK:
MESOSCALE DISCUSSION 2277 NWS STORM PREDICTION CENTER NORMAN OK 0636 AM CDT SAT OCT 29 2011 AREAS AFFECTED...PORTIONS NERN WV...SERN NY...NWRN MD INCLUDING PANHANDLE...CENTRAL/ERN PA...NWRN NJ...EXTREME NRN VA. CONCERNING...HEAVY SNOW VALID 291136Z - 291700Z PRIND HEAVIEST SNOW RATES THROUGH 18Z...AND MOST SUSTAINED AT 1-2 INCHES/HOUR...WILL BE OVER AND W OF BLUE RIDGE FROM NERN WV AND VA BORDER REGION NEWD ACROSS NWRN MD TO S-CENTRAL PA...SHIFTING NEWD ACROSS NERN PA INTO INTERIOR SERN NY BY ABOUT 18Z. RAIN SHOULD BECOME SNOW OVER PORTIONS CENTRAL-ERN PA THROUGH 16Z. ISOLATED CONVECTIVE BURSTS ALSO ARE POSSIBLE ALONG THAT PORTION OF RAIN/SNOW MIX ZONE FROM NRN VA TO SERN PA AND EVENTUALLY NWRN NJ. CONCENTRATION OF HEAVY SNOW POTENTIAL ACROSS DISCUSSION AREA WILL BE RELATED TO SEVERAL JUXTAPOSED REGIMES OF LIFT AND INSTABILITY. THESE INCLUDE...FROM TOP TO BOTTOM OF TROPOSPHERE... -- STRENGTHENING/NEWD-MOVING UPPER DIVERGENCE AS STG SHORTWAVE TROUGH...NOW EVIDENT IN MOISTURE CHANNEL IMAGERY OVER PORTIONS IL/INDIANA/WRN KY/TN...APCHS AREA WITH MORE NEGATIVE TILT. ASSOCIATED BAROCLINIC-LEAF SIGNATURE HAS BECOME VERY WELL-DEFINED WITH COOLING IR CLOUD TOPS ACROSS NRN WV AND WRN PA DURING PAST 2-3 HOURS. -- MIDLEVEL DCVA PRECEDING THAT TROUGH. -- NARROW SW-NE ALIGNED RIBBONS OF MIDLEVEL CONDITIONAL SYMMETRIC INSTABILITY SUPPORTING SLANTWISE CAPE UP TO ABOUT 200 J/KG. -- LOW-MIDDLE LEVEL FRONTOGENETIC FORCING...ESPECIALLY STRONG 15-18Z OVER S-CENTRAL THROUGH NERN PA AND INTERIOR SERN NY PER SREF GUIDANCE. -- ZONE OF ELEVATED CONVECTIVE INSTABILITY IN LOW-MIDDLE LEVELS...INVOF RAIN/SNOW TRANSITON ZONE...SUPPORTING 100-300 J/KG ELEVATED MUCAPE OVER ERN FRINGES OF DISCUSSION AREA THAT IN TURN CAN ENABLE CONVECTIVELY AIDED SNOW BURSTS WITH OCNL THUNDER. MODIFIED 6Z RNK/DCA RAOBS AND MODEL SOUNDINGS SUGGEST NEAR-SATURATION IN LOW LEVELS...PRECLUDING APPRECIABLE WET-BULB COOLING. HOWEVER...COLUMNAR DYNAMIC COOLING SHOULD OFFSET WAA IN ELEVATED CONVEYOR ENOUGH TO YIELD DOMINANT PRECIP TYPE AS SNOW OVER APPALACHIANS.