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.
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