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Winter Weather Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 2056Z 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
456 PM EDT WED OCT 29 2014

VALID 00Z THU OCT 30 2014 - 00Z SUN NOV 02 2014


DAY 1...


THE PROBABILITY OF HEAVY SNOW AND/OR SIGNIFICANT ICING IS LESS
THAN 10 PERCENT.


DAY 2...

UPPER GREAT LAKES...

A POTENT VORT WILL DIVE FROM CENTRAL CANADA INTO THE UPPER/WESTERN
GREAT LAKES LATE THURS/EARLY FRI BEFORE PROCEEDING INTO THE OH/TN
VALLEYS BY FRI NIGHT. THE DRAMATIC COLD ADVECTION ASSOCIATED WITH
THIS SHORT WAVE WILL PLUMMET SOUTH AND EAST FROM THE UPPER MS
VALLEY/GREAT LAKES TO THE SRN APPALACHIANS DURING THE FCST PERIOD
AND THE MOST OPPORTUNE PERIOD FOR HEAVY SNOW APPEARS TO BE FROM
THURS NIGHT TO FRI MORNING. A MODEST DYNAMIC COOLING REGIME ON THE
BACKSIDE OF DEVELOPING SURFACE LOW PRESSURE AND COLD AIR ALOFT
INTERACTING WITH THE WARM LAKES FOR QUITE A CONTRAST IN TEMPS
SHOULD RESULT IN RAIN TO RAIN/SNOW AND POSSIBLE SNOW ACCUMULATIONS
ACROSS THE UP OF MI AND NRN LOWER MI. A BLEND OF THE ECMWF/GFS AND
INTERNAL PSEUDO BIAS CORRECTED GUIDANCE FOR QPF AND THERMAL
PROFILES SUGGEST ONLY A LOW PROB OF 4 INCHES AS BOUNDARY LAYER
TEMPS BEING AN ISSUE. 

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.


DAY 3

CALIFORNIA...

A POWERFUL STORM SYSTEM OUT OVER THE PAC WILL GRADUALLY SPLIT ON
FRI ALLOWING THE SRN STREAM TO TAKE OVER ON SAT AND AN AGGRESSIVE
JET STREAK TO SLICE INTO CENTRAL CA AND NV BEFORE REACHING THE
INTER-MOUNTAIN WEST. SOME DECENT PAC MOISTURE TRANSPORT WITH VERY
FAVORABLE OROGRAPHICS SUGGEST MUCH NEEDED PRECIPITATION WITH SNOW
ACROSS THE CENTRAL/SRN SIERRA. IN FACT... A WPC BLEND OF THE
GLOBAL MODELS SUGGEST HEAVY SNOW PROBS OF UP TO A FOOT POSSIBLE.

CENTRAL/SOUTHERN APPALACHIANS...

THE FIRST SNOW OF THE SEASON APPEARS IMMINENT ON SAT ACROSS PARTS
OF THE CENTRAL/SRN APPALACHIANS WITH POTENTIALLY SIGNIFICANT
AMOUNTS. THE DYNAMIC SHORT WAVE TROUGH CARVING THROUGH THE GREAT
LAKES ON FRI WILL BOTTOM-OUT IN THE BASE OF THE LONG WAVE UPPER
TROUGH EXTENDING DOWN INTO THE SERN STATES. A POCKET OF ENHANCED
VERTICAL LIFT AND VERY COLD ANOMALOUS AIR ALOFT WILL SURGE ACROSS
THE OH VALLEY AND APPALACHIAN SPINE TO COMBINE WITH UPSLOPE FLOW
FOR STEADY SNOWFALL IN THE MTNS AND ACTUAL BUT MINOR ACCUMULATIONS
AWAY FROM THE TERRAIN. THE MODEL/FORECAST SPREAD HAS NARROWED
CONSIDERABLY AND WPC RELIED HEAVILY ON THE OPERATIONAL GFS/ECMWF
WITH THE INTERNAL PSEUDO BIAS CORRECTED GUIDANCE/MEAN FOR 4 AND 8
INCH HEAVY SNOW PROBS.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

MUSHER