SPC AC 051732
   
   DAY 2 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   1232 PM CDT TUE MAY 05 2009
   
   VALID 061200Z - 071200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS A LARGE PORTION OF THE
   SERN CONUS AND INTO THE RED RIVER VALLEY...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE UPPER MS
   VALLEY...
   
   ...SYNOPSIS...
   A PAIR OF MID-LEVEL SHORT-WAVE TROUGHS -- ONE IN THE NRN STREAM
   CROSSING THE N CENTRAL U.S./S CENTRAL CANADA AND A SECOND CROSSING
   THE MID MS/TN/OH VALLEYS -- WILL BE THE MAIN FEATURES ALOFT WITH
   RESPECT TO INFLUENCING THE CONVECTIVE FORECAST THIS PERIOD.
   
   AS THESE TWO FEATURES PROGRESS EWD...WEAK SHORT-WAVE RIDGING
   SPREADING ACROSS THE PLAINS AND ASSOCIATED LARGE-SCALE SUBSIDENCE
   SHOULD ACT TO LARGELY HINDER CONVECTIVE ACTIVITY FROM THE DAKOTAS
   INTO KS AND SWD ACROSS THE SRN HIGH PLAINS.
   
   AT THE SURFACE...A WEAK FRONTAL WAVE INITIALLY INVOF WRN TN SHOULD
   MOVE ENEWD TOWARD THE UPPER OH VALLEY THROUGH THE AFTERNOON...AS THE
   SRN STREAM MID-LEVEL TROUGH PROGRESSES EWD.  THE TRAILING SURFACE
   FRONT SHOULD LINGER FROM THE TN VALLEY WSWWD INTO CENTRAL TX. 
   FARTHER N...A WEAK FRONT ASSOCIATED WITH THE MORE NRN UPPER TROUGH
   SHOULD MOVE EWD OUT OF THE DAKOTAS AND ACROSS THE MO/UPPER MS
   VALLEYS...AND INTO THE UPPER GREAT LAKES REGION. 
   
   ...CAROLINAS WWD INTO THE LOWER MS VALLEY...
   AN EWD-MOVING UPPER TROUGH CROSSING THIS REGION AND
   MOIST/DESTABILIZING AIRMASS AHEAD OF THE WEAK SURFACE FRONT SHOULD
   SUPPORT THE DEVELOPMENT OF WIDESPREAD SHOWERS AND THUNDERSTORMS
   ACROSS A LARGE PORTION OF THE SOUTHEAST CONUS.  WEAK LAPSE RATES AND
   GENERALLY LIMITED DEEP-LAYER WIND FIELD SHOULD LIMIT OVERALL STORM
   INTENSITY.  HOWEVER...OVERALL CAPE/SHEAR COMBINATION WILL LIKELY
   SUPPORT OCCASIONAL LOCALLY-SEVERE STORMS ACROSS A LARGE REGION FROM
   THE CAROLINAS WSWWD ACROSS PARTS OF AR/LA.  GREATEST THREAT WILL
   OCCUR DURING THE AFTERNOON...WITH THE OVERALL POTENTIAL DIMINISHING
   DIURNALLY THROUGH THE EVENING.
   
   ...RED RIVER VALLEY/ARKLATEX REGION...
   WIDESPREAD THUNDERSTORMS SHOULD BE SHIFTING E OF THIS REGION THROUGH
   THE MORNING...AS THE WWD BRANCH OF THE LOW-LEVEL JET VEERS/SHIFTS
   EWD WITH TIME INTO THE MID/LOWER MS VALLEY REGION.
   
   HOWEVER...WITH MOIST AIRMASS IN PLACE NEAR/S OF A WEAK SURFACE FRONT
   AND WITH THE ONSET OF DIURNAL HEATING AS LINGERING CLOUDS SHIFT
   EWD...MODERATE DESTABILIZATION IS FORECAST.  WHILE CAPPING INVERSION
   IS FORECAST ACROSS A LARGE PORTION OF THE SRN PLAINS AS WEAK
   SHORT-WAVE RIDGING SPREADS ACROSS THE AREA...LOCALIZED ENHANCEMENT
   IN LOW-LEVEL UVV -- MAINLY INVOF THE WEAK SURFACE FRONT AND ANY
   LINGERING CONVECTIVE BOUNDARIES -- SHOULD SUPPORT ISOLATED TO
   SCATTERED STORM REDEVELOPMENT DURING THE AFTERNOON.  WEAK/SELY
   LOW-LEVEL FLOW VEERING/INCREASING TO NEAR 30 KT FROM THE WNW AT MID
   LEVELS SHOULD BE SUFFICIENT FOR AT LEAST WEAK ORGANIZATION...LIKELY
   ALLOWING A FEW STRONGER/SEVERE STORMS TO EVOLVE.  MAIN THREATS WILL
   BE HAIL AND/OR LOCALLY-DAMAGING WINDS BEFORE STORMS DIMINISH DURING
   THE EVENING HOURS.
   
   ...UPPER MS VALLEY REGION...
   MARGINAL DESTABILIZATION /AOB 1000 J/KG MIXED-LAYER CAPE/ IS
   FORECAST THROUGH THE AFTERNOON ACROSS PARTS OF THE MID MO/UPPER MS
   VALLEYS AHEAD OF THE APPROACHING/WEAK SURFACE FRONT...AS DAYTIME
   HEATING OF A MODESTLY-MOIST BOUNDARY LAYER OCCURS BENEATH THE EWD
   ADVECTION OF COOLER MID-LEVEL AIR/STEEPER LAPSE RATES.
   
   WITH MODERATE/WEAKLY-VEERING FLOW WITH HEIGHT EXPECTED ACROSS THIS
   REGION...DEVELOPING AFTERNOON STORMS INVOF THE FRONT SHOULD BECOME
   LOCALLY-ORGANIZED/SEVERE.  GIVEN LINEAR FORCING FAVORING LINE
   SEGMENTS AND WNWLY FLOW ALOFT...PRIMARY SEVERE THREAT -- IN ADDITION
   TO HAIL -- WILL LIKELY BE LOCALLY-DAMAGING WINDS WITHIN SEWD-MOVING
   STORM CLUSTERS.  THREAT SHOULD DIMINISH INTO THE EVENING AS HEATING
   DIMINISHES AND THE LOW-LEVEL AIRMASS STABILIZES.
   
   ...SERN OH/WRN WV INTO ERN KY/TN...
   ZONE OF ENHANCED DEEP-LAYER FLOW IS FORECAST TO SPREAD ACROSS THIS
   REGION AS THE MID-LEVEL SHORT-WAVE TROUGH AND AN ASSOCIATED SURFACE
   FRONTAL WAVE CROSS THE TN/MID OH VALLEYS.  POTENTIAL FOR
   DESTABILIZATION APPEARS LIMITED W OF THE APPALACHIANS FROM ERN TN
   NWD...AS WIDESPREAD CLOUDS/PRECIPITATION OVERSPREAD THIS REGION AS
   LOW-LEVEL JET AND ASSOCIATED/BROAD ZONE OF WARM ADVECTION SHIFTS
   INTO THIS AREA.  WHILE STRONG/VEERING FLOW WITH HEIGHT WOULD SUPPORT
   SEVERE/SUPERCELL STORMS...SEVERE THREAT LIKELY IS TO BE TEMPERED BY
   AN OVERALL LACK OF FAVORABLE INSTABILITY.  THUS...WILL MAINTAIN ONLY
   LOW-END SLIGHT RISK/15% SEVERE PROBABILITY ACROSS THIS REGION FOR A
   FEW STRONGER STORMS WHICH MAY EVOLVE IN CONJUNCTION WITH THE
   APPROACH OF THE SURFACE SYSTEM.
   
   ..GOSS.. 05/05/2009
   
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