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Winter Weather Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0725Z Oct 29, 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
325 AM EDT WED OCT 29 2014

VALID 12Z WED OCT 29 2014 - 12Z SAT NOV 01 2014


DAYS 1 AND 2

UPPER GREAT LAKES...

THE PROBABILITY FOR 4 INCHES OF SNOW ACROSS THE UPPER PENINSULA OF
MICHIGAN THURSDAY NIGHT INTO FRIDAY HAVE INCREASED SINCE YESTERDAY
AS THE MODEL SPREAD CONTINUES TO NARROW TOWARD A CONSENSUS.  THE
MIXED RAIN/SNOW EVENT...WITH A HIGHER PROBABILITY OF SNOW INLAND
AND AWAY FROM THE INFLUENCE OF THE WATER WATERS UPON BOUNDARY
LAYER TEMPERATURES...SHOULD BE BRIEF AS THE ASSOCIATED SHORTWAVE
TROUGH PASSES QUICKLY WITH FAVORABLE THERMODYNAMIC PROFILES
LASTING FOR ABOUT 6 TO 9 HOURS.  PREFERRED THE SREF MEAN THE MOST
TO DERIVE THE PROBABILITIES...BUT SOME GFS AND ECMWF WERE ALSO
INCLUDED TO PROVIDE A MORE COMPREHENSIVE AND SLIGHTLY LARGER
SOLUTION ENVELOPE.  THE FINAL RESULT IS MODERATE PROBABILITIES OF
4 INCHES ACROSS THE UPPER PENINSULA OF MICHIGAN.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

DAY 3

CALIFORNIA...

SOME MUCH NEEDED PRECIPITATION WILL LIKELY DEVELOP OVER MUCH OF
CENTRAL AND NORTHERN CALIFORNIA BY FRIDAY/FRIDAY NIGHT AS A
SIGNIFICANT AND SLOW MOVING SHORTWAVE TROUGH CROSSES THE
REGION...WITH SNOW LEVELS POSSIBLY AS LOW AS 5000 FT DEVELOPING
OVER THE SIERRAS.  USED A 3-WAY BLEND INVOLVING THE SREF
MEAN/GFS/ECMWF TO DERIVE THE AMOUNTS AND RESULTING
PROBABILITIES...WITH MODERATE PROBABILITY OF 4 INCHES FOR THE
SIERRAS.

CENTRAL/SOUTHERN APPALACHIANS...

A NARROW BUT POTENTIALLY SIGNIFICANT AXIS OF SNOW MAY ACCOMPANY
THE DEFORMATION ZONE OF A POTENT SHORTWAVE CROSSING THE
CENTRAL/SOUTHERN APPALACHIANS FRIDAY INTO FRIDAY NIGHT AS WELL AS
A REGION OF ENHANCED UPSLOPE FLOW TO ITS SOUTH IF THE
ASCENT/MOISTURE CAN DEVELOP SUFFICIENTLY HIGH INTO THE DENDRITIC
GROWTH ZONE.  MODELS CONTINUE TO SHOW CONSIDERABLE SPREAD WITH THE
TRACK OF THE MID/UPPER LEVEL CENTER...WITH THE GFS/GEFS MEAN/SREF
MEAN CLOSEST TO THE MODEL CONSENSUS...AND THEREFORE USED THEIR
LIQUID EQUIVALENT AMOUNTS AND THERMAL PROFILES THE MOST TO DERIVE
THE SNOW AMOUNTS AND PROBABILITIES.  THE ECMWF CAMP OF SOLUTIONS
WHICH HAS CONSISTENTLY REPRESENTED THE FASTER HALF OF THE GUIDANCE
REPRESENTS THE FINAL THIRD OF THE GUIDANCE TO ACCOUNT FOR THE
CONTINUED UNCERTAINTY.  GIVEN THAT THE ASSOCIATED SHORTWAVE TROUGH
STILL RESIDES OVER NORTHERN CANADA AND THEREFORE RECEIVES MINIMAL
DATA SAMPLING FOR INITIALIZATION...EXPECT THE SOLUTIONS TO
CONTINUE TO FLUCTUATE FOR ANOTHER 24 TO 36 HOURS.  BASED ON THE
CURRENT AVAILABLE GUIDANCE...MODERATE PROBABILITIES OF 4 INCHES
EXIST ACROSS SOUTHERN WEST VIRGINIA...WITH SLIGHT PROBABILITIES OF
4 INCHES EXTENDING SOUTHWARD INTO THE SMOKIES.  A FEW OF THE SREF
AND ECMWF ENSEMBLE MEMBERS SHOW A POSSIBILITY OF 8 INCHES ACROSS
PARTS OF THE CENTRAL AND SOUTHERN APPALACHIANS INTO THE
SMOKIES...ENOUGH TO SUPPORT ABOUT A 5 TO 10 PERCENT PROBABILITY.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

JAMES