The forecast challenge is how fast the warm air will come up the east coast and change the snow to rain. If the cold air holds on at the surface, some of the rain will freeze on already-frigid surfaces.
From the Saturday morning NYC NWS office forecast discussion:
The NWS was expecting the highest amount of snow and freezing rain from NE NJ though the Hudson Valley into SW CT, but that axis is forecast further east now…..
GENERAL EXPECTATION IS A 1 TO 4 INCH SNOWFALL ACROSS NYC/LONG
ISLAND WITH A GLAZE TO A FEW HUNDREDTHS OF AN INCH OF ICE...AND A
3-7 INCH SNOWFALL ELSEWHERE...HEAVIEST ACROSS INTERIOR PORTIONS OF
S CT. ALSO OUTSIDE OF NYC AND LONG ISLAND...THERE WILL BE A BAND
OF UP TO A TENTH OF AN INCH OF ICE IN A CORRIDOR RUNNING FROM NE
NJ INTO SW CT...AND UP TO A GLAZE TO A FEW HUNDREDTHS OF AN INCH
ICE ELSEWHERE...EXCEPT FOR ORANGE COUNTY...WHICH LOOKS TO REMAIN
ONLY SNOW AT THIS TIME.
The storm ends rapidly with the passage of a cold front whipped around the storm, midday Sunday.
ANOTHER THEME IN THE 00Z [7pm Friday computer model forecasts ]
SOLUTIONS...ONE THAT BUILDS IN THE
TRENDS FROM LAST NIGHT...IS THAT THE PRECIPITATION SHOULD COME TO
AN END FAIRLY RAPIDLY ON SUNDAY FROM NW TO SE...BASED ON A FASTER
TIMING OF THE COLD FRONT MOVING THROUGH.
Then more deep freeze for the northeast, followed by a storm passing off the eastern seaboard Tuesday night/Wednesday.
The computer models are moving the storm further away from the east coast with each run, but recently….
TUESDAY NIGHT INTO WEDNESDAY...LARGE DIFFERENCES REMAIN AMONGST THE
GLOBAL MODELS. THE GFS REMAINS WELL OFFSHORE BUT THE 12Z/20 EC
PASSES JUST OUTSIDE THE BENCHMARK WITH AN INVERTED TROUGH AFFECTING
THE REGION. 00Z/21 EC HAS TRENDED TOWARDS THE GFS...BUT AT THIS
POINT DO NOT WANT TO MAKE HUGE CHANGES TO THE FORECAST SINCE THIS
SCENARIO HAS BEEN OCCURRING ALL WINTER WHERE A COASTAL LOW SHIFTS
OFFSHORE AND THEN COMES BACK A FEW RUNS LATER DUE TO THE DIFFICULTY
THE MODELS HAVE WITH PHASING NORTHERN AND SOUTHERN STREAM ENERGY.
THEREFORE...HAVE NOT MADE WHOLESALE CHANGES TO THE FORECAST AT THIS
POINT. CHANCE SNOW REMAINS TUE NIGHT THROUGH WED AS AN ALBERTA
CLIPPER PASSES NORTH OF THE AREA AND A SHORT WAVE PASSES SOUTH OF
THE AREA. STAY TUNED.
WEDNESDAY NIGHT THROUGH FRIDAY...YET ANOTHER ARCTIC SURGE WILL CLOSE
OUT THIS EXTREMELY COLD MONTH OF FEBRUARY WITH TEMPS AVERAGING AT
LEAST 15 DEGREES BELOW NORMAL.