12/20 & 12/22 Slight Risk from the SPC

[Eric]

MESOSCALE DISCUSSION 2391
   NWS STORM PREDICTION CENTER NORMAN OK
   0102 PM CST THU DEC 22 2011
   
   AREAS AFFECTED...PARTS OF CNTRL/NRN GA / UPSTATE SC / FAR WRN NC /
   SERN TN
   
   CONCERNING...SEVERE POTENTIAL...WATCH LIKELY
   
   VALID 221902Z - 222100Z
   
   A TORNADO WATCH WILL LIKELY BE NEEDED BETWEEN 20-21 UTC.  THE RISK
   FOR AN ISOLD TORNADO OR TWO WILL INCREASE LATER THIS AFTERNOON INTO
   THE EARLY EVENING HOURS FROM W TO E ACROSS THE AREA.
   
   18Z SURFACE MESOANALYSIS PLACES A 1011 MB LOW INVOF BHM WITH A
   STATIONARY FRONT EXTENDING NEWD INTO FAR NWRN GA AND INTO THE NC
   SMOKY MTNS.  THE AIRMASS AHEAD OF THE LOW AND S OF THE BOUNDARY
   CONTINUES TO DESTABILIZE DUE IN PART TO A NWD FLUX OF RICHER GULF
   MOISTURE MOVING N/NEWD INTO THE AREA.  AN AREA OF MAXIMUM SURFACE
   PRESSURE FALLS /3.5 MB PER 2 HRS/ EXISTS IMMEDIATELY AHEAD OF THE
   LOW INTO FAR NWRN GA.  KFFC VAD HAS SHOWN 1 KM FLOW INCREASE FROM
   25-40 KTS THE PAST 3 HRS.  THIS IS INDICATIVE OF THE LOW LEVEL JET
   MIGRATING NEWD TOWARDS THE SPINE OF THE APPALACHIANS FROM THE NRN
   GULF COAST AS THE PRIMARY MID-LEVEL VORTICITY MAXIMUM MOVES FROM THE
   LOWER MS RIVER VALLEY TO THE LOWER OH VALLEY BY THIS EVENING.
   DESPITE RATHER MARGINAL LAPSE RATES...GRADUAL THETA-E INCREASE WITH
   TIME WILL SUPPORT 250-750 J/KG SBCAPE...SUPPORTIVE OF ROBUST
   UPDRAFTS.  WITH THE BACKGROUND WIND FIELD FEATURING 300-600 M2/S2
   EFFECTIVE SRH PER RUC FORECAST SOUNDINGS...THIS WILL BE MORE THAN
   EASILY SUPPORTIVE OF SEVERAL ORGANIZED AND ROTATING...LINEARLY
   ORIENTED STORMS.  AN ISOLD TORNADO THREAT...IN ADDITION TO WIND
   DAMAGE...WILL EXIST WITH ANY MESOVORTICIES AND EMBEDDED
   MESOCYCLONES.