SPC AC 131957
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0157 PM CST SAT MAR 13 2010
   
   VALID 132000Z - 141200Z
   
   ...NO SVR TSTM AREAS FORECAST...
   
   ...NC/VA INTO THE EVENING...
   THE 5 PERCENT HAIL PROBABILITY HAS BEEN REDUCED IN AREAL COVERAGE
   AND NOW EXTENDS FROM NERN NC INTO SERN VA.  TRENDS IN SURFACE
   OBSERVATIONS INDICATED DEWPOINTS HAVE BEEN FALLING TODAY AS SWLY
   WINDS ADVECT A DRIER CP AIR MASS INTO THIS REGION...WITH VALUES IN
   THE MID 50S NOW CONFINED TO NERN NC TO ERN VA/DELMARVA.  DESPITE
   CONTINUED COOLING OF MID LEVEL TEMPERATURES WITH THE APPROACH OF THE
   LARGE CLOSED LOW...NOW CENTERED OVER NRN AL/SRN MIDDLE TN...GREATER
   INSTABILITY VALUES SHOULD BE CONFINED TO NERN NC/SERN VA WHERE
   STRONGER SURFACE HEATING AND DEWPOINTS RESIDE. THE LEADING EDGE OF
   STRONGER ASCENT ATTENDANT TO A SHORTWAVE TROUGH TRACKING NEWD FROM
   GA/SC MAY SUPPORT NEW TSTM DEVELOPMENT INTO NERN NC/SERN VA LATER
   THIS AFTERNOON.  AS FORECAST EARLIER...THE COLD TEMPERATURES ALOFT
   AND MODEST INSTABILITY COULD SUPPORT ISOLATED STORMS WITH HAIL NEAR
   THE 1 INCH CRITERION.
   
   ..PETERS.. 03/13/2010
   
   .PREV DISCUSSION... /ISSUED 1015 AM CST SAT MAR 13 2010/
   
   ...SYNOPSIS...
   TWO PRIMARY SYNOPTIC SYSTEMS WILL AFFECT THE CONUS THIS PERIOD -- A
   BROAD CLOSED LOW WILL MOVE EWD FROM THE MID SOUTH TO THE
   CAROLINAS...AND AN UPSTREAM SHORTWAVE TROUGH WILL PROGRESS ESEWD
   FROM THE GREAT BASIN TO THE FOUR CORNERS.  THE LATTER WAVE WILL BE
   ACCOMPANIED BY CONDITIONALLY UNSTABLE LAPSE RATES AND A FEW
   THUNDERSTORMS IN THE LEFT EXIT REGION OF THE MID-UPPER JET. 
   HOWEVER...THE THREAT FOR DAMAGING WINDS APPEARS TO BE MINIMAL GIVEN
   VERY WEAK INSTABILITY WITH MARGINAL LOW-MIDLEVEL MOISTURE. 
   ADDITIONALLY...THE POTENTIAL FOR MOMENTUM TRANSFER WILL BE LIMITED
   BY MEAN LOW-LEVEL FLOW AOB 25 KT THIS AFTERNOON IN THE AREA OF
   EXPECTED THUNDERSTORM DEVELOPMENT.
   
   ...NC/VA THIS AFTERNOON/EVENING...
   THE CLOSED LOW CENTERED OVER WRN TN AS OF MID MORNING WILL CONTINUE
   EWD TO CAROLINAS THIS EVENING/TONIGHT.  RESIDUAL BOUNDARY LAYER
   DEWPOINTS IN THE LOW-MID 50S...DAYTIME HEATING...AND COOLING MID
   LEVEL TEMPERATURES /NEAR -24 C AT 500 MB/ WILL CONTRIBUTE TO THE
   DEVELOPMENT OF SBCAPE VALUES ON THE ORDER OF 500-1000 J/KG THIS
   AFTERNOON ACROSS NC/SRN VA.  THUNDERSTORM DEVELOPMENT WILL BE
   FOCUSED THIS AFTERNOON IN NC AS AN EMBEDDED SPEED MAX PIVOTS NEWD
   FROM GA...WITH CONVECTION EXPECTED TO SPREAD NEWD TO SRN VA THIS
   EVENING.  THOUGH VERTICAL SHEAR WILL WEAKEN WITH TIME IN PROXIMITY
   TO THE MID LEVEL LOW...THE COLD TEMPERATURES ALOFT AND MODEST
   INSTABILITY COULD SUPPORT ISOLATED STORMS WITH HAIL NEAR THE 1 INCH
   CRITERION.
   
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