PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD
441 PM EDT SAT OCT 27 2012

VALID 00Z SUN OCT 28 2012 - 00Z WED OCT 31 2012(edited~danielw)

DAYS 2 AND 3...

...CENTRAL/SOUTHERN APPALACHIANS...

THE FCST IS STILL HIGHLY UNCERTAIN WITH THE TRACK OF SANDY AND ITS
INTERACTION WITH THE CLOSED LOW DEVELOPING OVER THE APPALACHIANS.
GUIDANCE INDICATES A SURGE OF TROPICAL MOISTURE ADVECTING INTO THE
MID-ATL REGION AND WRAPPING AROUND THE INTENSE CYCLONE.
THE MODELS ALL SHOW ENOUGH ANOMALOUS LOWERING OF HEIGHTS WITH
STRONG DYNAMIC COOLING TAKING PLACE FOR TEMPERATURES TO BECOME
COLD ENOUGH FOR HVY SNOWFALL ACROSS THE CENTRAL AND SRN
APPALACHIANS LATE SUN INTO TUE. THE INITIAL SNOWS LATE SUN INTO
MON MORNING WILL OCCUR ACROSS THE TERRAIN NEAR THE NC/TN BORDER
INTO AREAS NEAR THE KY/VA BORDER. THIS IS WHERE THE GUIDANCE
SHOWS THE MAX COLD ADVECTION AND WHERE 850 MB TEMPERATURES DROP
BELOW FREEZING. NWRLY FLOW DEVELOPS AND PRODUCES SNOW IN TERRAIN
FACING THE FLOW. AS SUN NIGHT PROGRESSES THE AREA OF COLDER TEMPS
EXPENDS NORTH ACROSS WV AND RAIN CHANGES TO SNOW. AS A
RESULT...THE PROBABILITY UNCERTAINTIES REVOLVE AROUND THE
PRECIPITATION TYPE AND DURATION OF SNOW. ON MON
AFTERNOON/NIGHT... TREMENDOUS NWRLY UPSLOPE FLOW WILL INUNDATE THE
CENTRAL APPALACHIANS FOR HVY WET SNOW ACROSS HIGHER ELEVATIONS OF
WV/EASTERN KY/WESTERN VA AND NEAR THE NC/TN BORDER.

SIGNIFICANT APPALACHIANS SNOWFALL IS LIKELY BUT A WIDE VARIABILITY
PERSISTS ON ACCUMULATIONS AMONG THE MODEL AND ENSEMBLE SOLUTIONS.
POTENTIAL EXISTS FOR 2-3 FEET OF SNOW IN PARTS OF THE HIGHER
CENTRAL APPALACHIANS.
SNOW ACCUMULATIONS AWAY FROM THE TERRAIN MAY DEVELOP TUE AS
HEIGHTS/TEMPS GRADUALLY FALL. THE 12Z NAM HAD THE COLDEST TEMPS
OFF ALL SOLUTIONS AND WAS DISCOUNTED IN FAVOR OF THE 09Z SREF
MEAN/12Z GEFS MEAN/00-12Z ECMWF/12Z UKMET/12Z GFS/12Z GEFS MEAN.
THIS MAJORITY CLUSTER OF SOLUTIONS WAS USED FOR QPF/TEMPERATURE
PROFILES TO DERIVE SNOWFALL PROBABILITIES.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

PETERSEN