Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 262030
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
329 PM EST WED NOV 26 2014

VALID 00Z THU NOV 27 2014 - 00Z SUN NOV 30 2014

DAYS 1 TO 3...

...NORTHEAST/NEW ENGLAND...
THE COASTAL LOW BEGINNING TO TAKE FORM OFF THE MID-ATL COAST THIS
AFTN WILL DEEPEN AND RAPIDLY LIFT UP THE NORTHEAST COAST THIS
EVENING/OVERNIGHT BEFORE ROLLING UP INTO THE CANADIAN MARITIMES ON
THANKSGIVING DAY. THUS THE THREAT FOR VERY HEAVY SNOWFALL IS STILL
ANTICIPATED FROM THE HUDSON VALLEY OF NY TO ALMOST THE ENTIRETY OF
MAINE. THE BAROCLINIC LEAF/OPEN WAVE STRUCTURE OF THE PRECIP
SHIELD EARLIER TODAY IS BEGINNING TO DEVELOP INTO A PRONOUNCED
DEFORMATION ZONE/COMMA HEAD REPRESENTATION. THIS IS DUE TO THE
STRENGTHENING OF THE SURFACE LOW OFF THE COAST ALLOWING STRONG
DYNAMIC COOLING TO OCCUR AND LIKELY BANDS OF FRONTOGENESIS AND
BANDING TO THE HEAVY SNOW. THE HEAVIEST SNOW WILL STILL REMAIN
MAINLY INLAND AND AWAY FROM THE IMMEDIATE COAST WITH THE GREATER
THAN 12 INCH PROBS ACROSS CENTRAL MAINE INTO NRN NH. WPC FOLLOWED
A BLEND OF THE 12Z GUIDANCE OVERALL FOR THE ENTIRE HEAVY SNOW
PROBS.

...LOWER OHIO VALLEY/TENNESSEE VALLEY AND SRN APPALACHIANS...
A DIGGING SHORTWAVE TROUGH OVER THE MID MISSISSIPPI VALLEY WILL
REACH THE TENNESSEE VALLEY/LOWER OHIO VALLEY INTO THE SRN
APPALACHIANS THIS EVENING/OVERNIGHT BEFORE THE BOLD IMPULSE
REACHES JUST OFFSHORE OF COASTAL VA/NC BY THANKSGIVING NIGHT. THIS
PROGRESSIVE FEATURE DOES NOT HAVE MUCH MOISTURE TO WORK WITH...
SINCE IT IS FOLLOWING THE WET EAST COAST SYSTEM AND SURFACE HIGH
PRESSURE BUILDING QUICKLY IN FROM UPSTREAM. A WEAKENING SURFACE
LOW ASSOCIATED WITH THIS SYSTEM NEAR SRN IA/NRN MO WILL TRACK TO
ERN/SERN MO THIS EVENING AND TO THE TN VALLEY OVERNIGHT AND STRONG
FORCING ALOFT... UPPER JET AND DIFLUENT EXIT REGION... SHOULD
YIELD A STREAK OF LIGHT SNOW. THE NAM/ECMWF PINPOINT AN AXIS OF
LIGHT SNOW FROM WRN/SRN KY TO NERN TN AND THE SRN APPALACHIANS AND
WPC FOLLOWED SUITE BY ISSUING A LOW PROB OF 4 INCHES. AS THE
SYSTEM JUMPS TO THE COAST ON THANKSGIVING DAY... EVEN A FEW
FLURRIES OR SNOW SHOWERS COULD BE POSSIBLE ACROSS SRN VA/NRN NC
WITH VERY MINIMAL IF ANY ACCUMULATIONS.

...PACIFIC NORTHWEST/NORTHERN ROCKIES/NORTHERN PLAINS/UPPER
MIDWEST...

A MOIST ONSHORE REGIME INTO THE PAC NW AND OVER THE TOP OF A
DE-AMPLIFYING WESTERN RIDGE WILL YIELD VERY HEAVY OROGRAPHIC
SNOWFALL FROM THE NRN WA CASCADES INTO THE BITTERROOTS AND NRN
ROCKIES ON THANKSGIVING DAY/FRI AND SOME OF THIS MOISTURE WILL
OVERRUN A POLAR BOUNDARY INTO THE COLD SECTOR. LIGHT SNOW WITH
FREEZING DRIZZLE WILL START FROM THE NRN PLAINS BUT GRADUALLY
PRESS DOWNSTREAM THROUGH THE DAKOTAS INTO MN/WI. THEN BY SAT...
THE MOISTURE FEED INTO THE PAC NW WILL SINK SOUTH INTO NRN CA...
AS A SIGNIFICANT POLAR/ARCTIC SHORT WAVE DIGS THROUGH BRITISH
COLUMBIA INTO WA/OR. THE CRASHING OF UPPER HEIGHTS ACROSS THE
NW/NRN INTER-MOUNTAIN WEST WILL LOWER SNOW LEVELS AND INCREASE THE
PROBS FOR HEAVY SNOWFALL. OVERALL WPC FOLLOWED A BLEND OF THE
GUIDANCE... AS ONLY MINIMAL SPREAD EXISTS.

THE PROBABILITY FOR SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

MUSHER

$$




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