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Winter Weather Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 2149Z Nov 25, 2014)
 
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Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
449 PM EST TUE NOV 25 2014

VALID 00Z WED NOV 26 2014 - 00Z SAT NOV 29 2014

DAYS 1 THROUGH 3...

...APPALACHIANS/MID ATLANTIC/NORTHEAST/NEW ENGLAND...

THE FIRST SNOWFALL OF THE SEASON... ON ONE OF THE BUSIEST TRAVEL
DAYS OF THE YEAR... WILL IMPACT AREAS OF THE CENTRAL/SRN
APPALACHIANS TO NEW ENGLAND. HOWEVER IT APPEARS AT THE MOMENT THE
MAJOR URBAN SPAN FROM DC TO BOS WILL BE SPARED FOR THE MOST PART.

A POTENT UPPER SHORT WAVE TROUGH BEGINNING TO ROUND THE BASE OF AN
ANOMALOUS AMPLIFIED LONG WAVE TROUGH WILL LIFT NORTH AND EAST
THROUGH THE GULF COAST REGION AND UP THROUGH THE ERN SECTION OF
THE COUNTRY. THIS IMPULSE WILL INDUCE AN AREA OF LOW PRESSURE OVER
THE EAST CENTRAL GULF OF MEXICO BEFORE JUMPING TO THE SC/NC COAST
AND RACING UP THE EASTERN SEABOARD. THIS SYSTEM WILL CAPTURE A
SURPLUS IN AVAILABLE LOW LEVEL MOISTURE CONTENT FOR AN EXTREMELY
WET 24 TO 36 HRS OF RAIN AND SNOW.

THE BIG QUESTION MARK WITH THIS SYSTEM AND TYPICALLY THIS TIME OF
THE YEAR IS SUSPECT BOUNDARY LAYER TEMPS AND THE LACK OF COLD AIR
IN PLACE ACROSS THE MID-ATL REGION INTO THE NORTHEAST. THE
GUIDANCE IS UNANIMOUS THAT UNTIL THE SURFACE LOW BEGINS TO DEEPEN
RAPIDLY... WHICH IS WED MIDDAY TO LATE AFTN OFF THE DELMARVA OR
NJ/LONG ISLAND... THAT THE THERMAL COLUMN WILL NOT TRULY BE
CONDUCIVE FOR HEAVY SNOWFALL. THIS IS WHEN DYNAMIC COOLING AND A
HEALTHY DEFORMATION ZONE/COMMA HEAD WILL FORM AND SURFACE TEMPS
WILL NOT BE A ISSUE.

THE OTHER OINTMENT IN THE FORECAST IS POSSIBLE ENHANCED RAINS AND
CONVECTION THATS OCCURRING ACROSS THE FL PENINSULA AND ANTICIPATED
ALONG THE OUTER BANKS OF NC/GULF STREAM THAT WILL PROHIBIT THE
PLETHORA OF MOISTURE TO SPREAD BACK INTO THE COLD SECTOR AND
ENHANCE.

OVERALL THE MODEL GUIDANCE SHOW VERY MINIMAL SPREAD WITH MASS
FIELDS ON THIS SYSTEM AND THE IMPENDING UPSTREAM NRN POLAR SHORT
WAVE DIVING INTO THE OH/TN VALLEYS AND KICKING THIS SYSTEM OUT.
HOWEVER... THE 12Z NAM SHOWS OUTLYING DETAILS ON HEAVIER QPF IN
THE COLD SECTOR OR NORTH AND WEST OF THE SURFACE LOW TRACK AND
COLDER THERMAL PROFILES/MORE SUFFICIENT SNOW PRECIP TYPE. WPC
REALLY PREFERRED THE 12Z GFS AND 00Z/25 ECMWF/EC MEAN ON THERMAL
PROFILES INDICATING A VERY TIGHT GRADIENT FROM RAIN TO SNOW RIGHT
ALONG THE I95 CORRIDOR. WPC ALSO PREFERRED INTERNAL GUIDANCE ON
QPF WITH THE GFS/ECMWF/SREF MEAN. THUS HEAVY SNOWFALL AXIS FROM
THE TERRAIN OF WEST VIRGINIA TO NORTHEAST PA/NORTHWEST NJ AND
POCONOS INTO THE SOUTHERN HUDSON VALLEY AND INTERIOR PORTIONS OF
NEW ENGLAND NWRN CT/WRN MA/SRN VT/NH. THIS IS WHERE WPC PLACED THE
4 TO 12 INCH HEAVY SNOW PROBS. THIS DOES NOT MEAN THE MAJOR METRO
CENTERS WILL NOT SEE SNOW BUT EXPECT MAINLY RAIN CHANGING OVER TO
SNOW WITH MINIMAL ACCUMULATIONS.

...UPPER MIDWEST TO CENTRAL/SRN APPALACHIANS...

A MOISTURE DEPRIVED SHORTWAVE ALONG THE NRN STREAM DIGGING INTO
ND/SD THIS AFTN AND WILL DIVE SOUTHEASTWARD TOWARD THE LOWER OH
VALLEY/TN VALLEY AND CENTRAL/SRN APPALACHIANS OVER THE NEXT 24 HRS
INTO THANKSGIVING MORNING. A STREAK OF WARM ADVECTION AND
DYNAMICALLY DRIVEN LIGHT SNOW WILL BE EXPECTED... MAINLY FROM ERN
DAKOTAS INTO IA/SRN MN BEFORE REACHING THE HILLS/TERRAIN OF ERN
KY/NERN TN INTO SWRN VA/WRN NC WED NIGHT INTO THURS MORNING. WPC
STAYED VERY CLOSE TO A BLEND OF THE GFS AND ECMWF FOR 4 INCH HEAVY
SNOW PROBS.

...PACIFIC NORTHWEST/NORTHERN ROCKIES...

A SERIES OF SHORT WAVES AND MOIST PAC ONSHORE FLOW COMING INTO THE
PAC NW AND SLIDING OVER THE DE-AMPLIFYING EASTERN PACIFIC/WEST
COAST RIDGE WILL RESULT IN STEADY HEAVY OROGRAPHIC SNOWS IN THE WA
CASCADES/ID BITTERROOTS AND NRN ROCKIES AND A STREAK OF LIGHT
OVERRUNNING SNOW ACROSS THE NRN PLAINS INTO THE UPPER MIDWEST OR
POLAR AIR MASS. WPC FOLLOWED A BLEND OF THE GLOBAL MODELS WITH
PRISM DATA FOR THE HEAVY SNOW PROBS.

THE PROBABILITY FOR SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

MUSHER