Heavy Snow
Posted by JAC on 12/18/2009, 2:09 pm



MESOSCALE DISCUSSION 2257
  NWS STORM PREDICTION CENTER NORMAN OK
  1232 PM CST FRI DEC 18 2009
 
  AREAS AFFECTED...SMOKEY MTNS / PARTS OF WRN NC AND PIEDMONT / ERN TN
  / SWRN VA / SERN WV
 
  CONCERNING...HEAVY SNOW
 
  VALID 181832Z - 182230Z
 
  HEAVY SNOWFALL RATES AROUND 1 INCH PER HOUR WILL LIKELY COMMENCE
  FIRST ACROSS THE HIGHER ELEVATIONS OF THE SRN APPALACHIANS IN THE
  18-21Z PERIOD WITH MIXED PRECIPITATION OCCURRING ACROSS WRN PORTIONS
  OF THE NC PIEDMONT.  THE HEAVY SNOWFALL RATES WILL EXTEND NEWD INTO
  SWRN VA AND SERN WV 21-00Z.  LOCALIZED RATES AROUND 2 INCHES PER
  HOUR WITH POTENTIALLY HEAVIER BURSTS ARE POSSIBLE OVER E FACING
  SLOPES IN WRN NC AND PERHAPS SW VA LATE THIS AFTERNOON INTO THE
  EVENING HOURS.
 
  EARLY AFTERNOON SURFACE ANALYSIS PLACED A SURFACE WEDGE FRONT FROM
  PARTS OF SRN GA NEWD OVER THE ADJACENT SC/NC COASTAL WATERS.
  SURFACE TEMPS NEAR 32 DEG F ARE CONFINED MAINLY TO PORTIONS OF WRN
  NC AND SWRN VA.  WET BULBING COOLING IN AREAS OF STRONG ASCENT WILL
  SUPPORT A TRANSITION TO WET SNOW ACROSS ALL AREAS W OF I-85.  
 
  RADAR MOSAIC HAS SHOWN A SLUG OF HEAVIER PRECIPITATION MOVING NWD
  ACROSS NRN GA THE PAST FEW HOURS WITH MEASURED RAINFALL RATES
  0.20-0.30 INCH PER HOUR IN NRN GA AND WRN PART OF UPSTATE SC.  AS A
  LEAD SHORTWAVE TROUGH LOCATED OVER AL/GA MOVES NEWD TOWARDS THE SRN
  APPALACHIANS...STRENGTHENING H8-H6 FRONTOGENESIS AND STRONG
  MID-LEVEL UVV/S SPREADING NEWD ACROSS THE REGION WITHIN THE
  DENDRITIC GROWTH LAYER IN THE MID-LATE AFTERNOON HOURS.  WITH LITTLE
  EVIDENCE TO THE CONTRARY...ACCORDING TO RADAR MOSAIC EXTRAPOLATION
  AND MODEL CONSENSUS 6 HOURLY QPF...SNOWFALL RATES AOA 1 INCH PER
  HOUR ARE LIKELY.  RECENTLY DETECTED LIGHTNING OVER WRN NC INDICATES
  UPRIGHT CONVECTION EXISTS OVER A SMALL AREA EARLY THIS AFTERNOON.
  TOWARDS THIS EVENING...ETAKF/GFS FORECAST SOUNDINGS INDICATE THE
  POSSIBILITY FOR MORE WIDESPREAD UPRIGHT CONVECTION OVER THE E FACING
  SLOPES IN PARTS OF NWRN NC INTO SWRN VA.  THIS MAY SUPPORT LOCALIZED
  SNOW BURSTS APPROACHING 3 INCHES PER HOUR NEAR OR AFTER 00Z THIS
  EVENING.
 
  ..SMITH.. 12/18/2009
 
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Very Unstable Air pushing up from the GOM, Tornado Watch for South FL - JAC, 12/18/2009, 7:43 am
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