SPC AC 111253

   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0753 AM CDT MON MAY 11 2015

   VALID 111300Z - 121200Z

   ...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS SERN LOWER
   MI...OH...INDIANA...NRN KY...

   ...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS MID SOUTH ACROSS LOWER
   MS VALLEY TO S TX...

   ...THERE IS A MRGL RISK OF SVR TSTMS ELSEWHERE FROM S TX TO PORTIONS
   WRN/NRN NY...

   ...SUMMARY...
   SCATTERED THUNDERSTORMS ARE EXPECTED TO DEVELOP ALONG AND AHEAD OF A
   COLD FRONT OVER PARTS OF LOWER MICHIGAN TO THE OHIO VALLEY...AS WELL
   AS FROM THE MID SOUTH TO SOUTH TEXAS.  DAMAGING WINDS AND HAIL WILL
   BE POSSIBLE WITH THE STRONGER THUNDERSTORMS.  A COUPLE OF TORNADOES
   MAY OCCUR IN THE SOUTHERN GREAT LAKES REGION.

   ...SYNOPSIS...
   PROGRESSIVE MID/UPPER-LEVEL PATTERN IS FCST THROUGH
   PERIOD...FEATURING CYCLONES NOW EVIDENT IN MOISTURE-CHANNEL IMAGERY
   OVER ERN DAKOTAS AND OFFSHORE PAC NW.  NRN-PLAINS CYCLONE IS
   EXPECTED TO MOVE GENERALLY EWD ACROSS MN TODAY...DEVOLVING INTO
   OPEN-WAVE TROUGH TONIGHT ACROSS WI.  THIS WILL OCCUR AS ACCOMPANYING
   SHORTWAVE TROUGH NOW OVER CENTRAL HIGH PLAINS PIVOTS EWD OVER KS/NEB
   THEN NEWD ACROSS LM AND LOWER MI...AND ANOTHER PERTURBATION PIVOTS
   SEWD/EWD OUT OF BLACK HILLS REGION AND ACROSS MID-UPPER MS VALLEY. 
   PAC CYCLONE WILL MOVE SEWD TO SWRN ORE AND NWRN CA THROUGH
   PERIOD...AND SRN-STREAM PERTURBATION NOW SEEN OFF BAJA WILL EJECT
   ENEWD ACROSS NWRN MEX TOWARD FAR W TX AND BIG BEND REGION. 

   AT SFC...CYCLONE NOW OVER SRN MN IS EXPECTED TO MOVE ENEWD ACROSS
   WRN/NRN WI BY 00Z...THEN OCCLUDE...WITH NEW LOW EJECTING ENEWD
   ACROSS SWRN QUE DURING 09-12Z TIME FRAME. COLD FRONT...NOW EXTENDING
   FROM UPPER MS VALLEY ACROSS OZARKS TO CENTRAL/SW TX...IS PRECEDED
   ALONG MUCH OF ITS LENGTH BY CONVECTIVELY GENERATED
   OUTFLOW/BAROCLINIC BOUNDARY THAT IS EVIDENT FROM SRN IL TO NRN LA
   AND SE TX.  FRONT ITSELF SHOULD DECELERATE OVER S-CENTRAL/SE
   TX...PERHAPS MERGING WITH PREFRONTAL BOUNDARY THIS AFTN OR
   OVERNIGHT.  COLD FRONT SHOULD MOVE EWD TO LOWER MI...INDIANA AND
   CENTRAL/ERN AR BY 00Z...THEN TO ERN NY...CENTRAL/SRN APPALACHIANS
   AND CENTRAL MS AROUND END OF PERIOD.  WARM FRONT SHOULD MOVE NWD
   TODAY THROUGH PARTS OF WI...LM AND LOWER MI AHEAD OF SFC
   CYCLONE...AND MORE SLOWLY MOVE NWD ACROSS WRN/NRN NY.

   ...S TX TO LOWER MS VALLEY...
   REF SPC WW 163 AND RELATED MESOSCALE DISCUSSIONS FOR NEAR-TERM INFO
   ON SVR THREAT OVER S TX.

   ADDITIONAL SVR-TSTM DEVELOPMENT IS POSSIBLE TODAY OVER THIS CORRIDOR
   AS AIR MASS DESTABILIZES IN PRECONVECTIVE SECTOR...INCLUDING
   POTENTIAL RE-INTENSIFICATION OF CURRENTLY/MOSTLY ANAFRONTAL SQUALL
   LINE NOW EVIDENT FROM SERN AR TO SE TX.  DAMAGING WIND WILL BE
   POSSIBLE...AND LARGE-HAIL THREAT INCREASES WITH WWD EXTENT ACROSS S
   TX IN PROXIMITY TO STEEPER DEEP-LAYER LAPSE RATES AND LARGER DIURNAL
   CAPE.

   ALTHOUGH MID/UPPER-LEVEL TROUGH WILL BE EJECTING AWAY FROM THIS
   AREA...LEADING TO HEIGHT RISES...SUBTLE IMPULSES EMBEDDED WITHIN
   SWLY SUBTROPICAL PLUME...COMBINED WITH CONTINUED ADVECTION OF EML
   OFF HIGHER TERRAIN OF NRN MEX...WILL HELP TO MAINTAIN STEEP LAPSE
   RATES ALOFT.  MEANWHILE...COMBINATION OF MORE DIRECT LIFT FROM FOUR
   PRIMARY SOURCES SHOULD SUPPORT POTENTIAL FOR CONVECTIVE DEVELOPMENT
   ACROSS THIS SWATH TODAY...
   1. COLD POOLS FROM ANY ONGOING CONVECTION...ESPECIALLY LA/SE TX
   SECTOR...
   2. LEFTOVER OUTFLOW BOUNDARY/BOUNDARIES AND RELATED
   DIFFERENTIAL-HEATING ZONES EXTENDING FROM LA/SE TX TSTM AREA SWWD
   ACROSS S TX...
   3. FRONT...ESPECIALLY WHERE IT CAN ACCESS SUITABLY UNSTABLE
   WARM-SECTOR AIR THROUGH GAPS OR MESOBETA-SCALE RECOVERY ZONES BEHIND
   MORNING CONVECTION.  S TX SEEMS MOST PROBABLE FOR THIS PROCESS. 
   4. SFC DIABATIC HEATING AND RELATED DIFFERENTIAL-HEATING ZONES. 

   SVR POTENTIAL SHOULD DIMINISH LATE THIS EVENING OVER S-CENTRAL/SW TX
   AND WITH OFFSHORE MOVEMENT OF LEADING SQUALL LINE FARTHER E TODAY. 

   ...GREAT LAKES/OH VALLEY REGION TO MID SOUTH...
   ONE OR MORE BKN BANDS OF TSTMS ARE EXPECTED TO DEVELOP THROUGH AFTN
   AND MOVE NEWD ACROSS THIS REGION...OFFERING PRIMARILY DAMAGING-GUST
   RISK WITH A COUPLE TORNADOES ALSO POSSIBLE.  ALTHOUGH MID-UPPER
   LEVEL LAPSE RATES WILL BE MRGL...SUFFICIENT MOISTENING HAS OCCURRED
   SUCH THAT COOLING ALOFT SHEAR OF EJECTING CYCLONE...COMBINED WITH
   POCKETS OF DIURNAL SFC HEATING...WILL YIELD SUPPORTIVE INSTABILITY. 
   MUCAPE 500-1000 J/KG IS POSSIBLE...AMIDST 45-60 KT EFFECTIVE-SHEAR
   MAGNITUDES.  SUFFICIENT COMPONENT OF MEAN-WIND AND DEEP-SHEAR
   VECTORS ACROSS CONVECTIVE-BAND ORIENTATION IS EVIDENT TO SUGGEST
   DISCRETE STORM MODES AS WELL..INCREASING PROBABILITIES FOR A FEW
   SUSTAINED SUPERCELLS COMPARED TO AREAS FARTHER S AHEAD OF SFC COLD
   FRONT. 

   RELATIVE MIN IN SVR POTENTIAL IS APPARENT BETWEEN THESE TWO AREAS
   ACROSS LOWER OH VALLEY AND PARTS OF MID SOUTH...WHERE CONVERGENCE
   ALONG AND AHEAD OF COLD FRONT WILL BE RELATIVELY MINIMIZED DUE TO
   BOUNDARY-LAYER VEERING IN PRECONVECTIVE SECTOR...AND CONVECTIVE
   PLUME HAS OUTPACED SUBSTANTIAL WAA/MOISTURE-ADVECTION-RELATED
   DESTABILIZATION.  IN ADDITION...CLOUD COVER WILL LIMIT DIABATIC SFC
   HEATING OVER THIS AREA. 

   ...ERN NC/SERN VA...
   REMNANTS OF TD ANA WILL PROCEED NEWD ACROSS ERN SC AND OFFSHORE
   HAMPTON ROADS REGION THROUGH THIS EVENING.  DUE TO WEAKNESS OF BOTH
   INSTABILITY AND LOW-LEVEL SHEAR...AND LACK OF SUBSTANTIAL CONVECTIVE
   STRUCTURES...IN WEAKENING SYSTEM...SVR PROBABILITIES HAVE BEEN
   DROPPED.

   ..EDWARDS/MOSIER.. 05/11/2015

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