SPC AC 271618

   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   1118 AM CDT MON MAY 27 2013

   VALID 271630Z - 281200Z

   ...THERE IS A MDT RISK OF SVR TSTMS ACROSS PART OF S-CNTRL/SERN NEB
   AND N-CNTRL/NERN KS...

   ...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE GREAT PLAINS
   INTO OH VALLEY...

   ...SYNOPSIS...

   THE LARGE-SCALE PATTERN WILL BECOME MORE PROGRESSIVE THIS FORECAST
   PERIOD AS A STRONG UPPER-LEVEL JET STREAK DEVELOPS FROM THE NERN
   PACIFIC INTO THE GREAT BASIN AND SRN ROCKIES.  THIS WILL CONTRIBUTE
   TO THE INTENSIFICATION AND INCREASING NEGATIVE TILT OF A TROUGH FROM
   THE PACIFIC NW INTO SRN ROCKIES.  DOWNSTREAM FROM THESE
   DEVELOPMENTS...PHASED VORTICITY MAXIMA OVER SERN ID/WRN WY AND THE
   CNTRL HIGH PLAINS WILL PROGRESS NEWD TOWARD THE UPPER-MS
   VALLEY...SUPPRESSING THE MIDLEVEL HEIGHT FIELD ACROSS THE NRN INTO
   CNTRL PLAINS.

   IN THE LOW LEVELS...A LEE CYCLONE OVER NWRN KS WILL SLOWLY DRIFT EWD
   ALONG AN OUTFLOW-REINFORCED BAROCLINIC ZONE SITUATED ACROSS NRN KS. 
   A CONVECTIVE OUTFLOW BOUNDARY WILL LIKELY PERSIST TODAY ACROSS THE
   LOWER-MO VALLEY INTO OZARKS IN CONJUNCTION WITH AN ONGOING MCS. 
   FARTHER TO THE N AND E...A WEAK AREA OF LOW PRESSURE DEVELOPING NEWD
   THROUGH THE MID-MO VALLEY WILL ATTEMPT TO DRAW A WARM FRONT NWD
   THROUGH THE MIDWEST.  MEANWHILE...AN INVERTED TROUGH OVER THE NRN
   AND CNTRL HIGH PLAINS WILL TRANSITION TO A COLD FRONT WHILE
   PROGRESSING EWD.  FINALLY...A DRYLINE WILL MIX EWD TODAY ACROSS WRN
   KS...THE OK/TX PNHDLS...AND WRN TX.  

   ...CNTRL PLAINS THIS AFTERNOON INTO TONIGHT...

   12Z REGIONAL SOUNDINGS SHOW THE POTENTIAL FOR STRONG AIR MASS
   DESTABILIZATION /I.E. AFTERNOON MLCAPE VALUES APPROACHING 3000-4000
   J PER KG/ WITHIN THE WARM SECTOR OWING TO VERY STEEP MIDLEVEL LAPSE
   RATES ATOP A MOIST BOUNDARY LAYER CHARACTERIZED BY LOWEST-100-MB
   MEAN MIXING RATIOS OF 13.5-14.5 G/KG.  EXPLOSIVE TSTM DEVELOPMENT IS
   ANTICIPATED BY MID TO LATE AFTERNOON OVER N-CNTRL KS/S-CNTRL
   NEB...NEAR THE SURFACE TRIPLE POINT WHERE LOW-LEVEL CONVERGENCE IS
   MAXIMIZED.  HERE...FORECAST HODOGRAPHS SHOW PRONOUNCED VEERING OF
   WINDS WITH HEIGHT WITH 40-50 KT OF DEEP-LAYER SHEAR AND EFFECTIVE
   SRH OF 200-300+ M2/S2 BY THIS EVENING.  INTENSE SUPERCELLS APPEAR
   LIKELY WITH THE THREAT FOR TORNADOES /SOME POTENTIALLY SIGNIFICANT/
   AND VERY LARGE HAIL.  STORMS MAY GROW UPSCALE INTO A SEWD-MOVING MCS
   TONIGHT WITH A RISK FOR LARGE HAIL AND DAMAGING WINDS PERSISTING
   ACROSS PARTS OF ERN KS AND WRN/CNTRL MO.

   ADDITIONAL...WIDELY SCATTERED TSTMS ARE EXPECTED TO DEVELOP THIS
   AFTERNOON ALONG THE LEE TROUGH AND/OR FAVORED TERRAIN OVER ERN WY
   AND THE NEB PNHDL SWD INTO NERN CO.  HERE...THE COMBINATION OF
   MODERATE AMOUNTS OF INSTABILITY AND VERTICAL SHEAR WILL BE
   SUPPORTIVE OF ORGANIZED/ROTATING STORMS CAPABLE OF LARGE HAIL AND
   DAMAGING WINDS. 

   ...LOWER-MO/MID-MS VALLEYS INTO OH VALLEY THIS AFTERNOON AND
   EVENING...

   AN MCV APPEARS TO BE EVOLVING AS OF MID MORNING OVER NERN MO...ON
   THE NRN FLANK OF NOCTURNAL MCS ONGOING ACROSS THE LOWER-MO VALLEY. 
   LOW-LEVEL CONVERGENCE/UPLIFT ALONG THE LEADING EDGE OF MCS COLD POOL
   COUPLED WITH DEEPER-LAYER FORCING ASSOCIATED WITH MCV WILL LIKELY
   SUPPORT TSTM INTENSIFICATION BY EARLY AFTERNOON ALONG THE ERN FLANK
   OF THE SYSTEM.  THE EWD MIGRATION OF A SWLY LLJ WILL ENHANCE THE
   NEWD FLUX OF AN INCREASINGLY MOIST BOUNDARY LAYER THROUGH THE MID-MS
   INTO OH VALLEYS...BENEATH AN EWD-ADVECTING EML...SUPPORTING MODERATE
   AFTERNOON INSTABILITY AHEAD OF THE MCS.  GIVEN MODESTLY STRONG LOW
   TO MIDLEVEL FLOW...THE POTENTIAL WILL EXIST FOR ACCELERATION OF THE
   CONVECTIVE SYSTEM WITH A RISK FOR DAMAGING WINDS AND HAIL SPREADING
   EWD INTO THE OH VALLEY.  

   ...NRN HIGH PLAINS THIS AFTERNOON AND EVENING...

   TSTMS ONGOING ACROSS PARTS OF SERN MT/NERN WY/WRN SD SHOULD CONTINUE
   TO INCREASE IN COVERAGE AND INTENSITY TODAY AS FORCING FOR ASCENT
   INCREASES AHEAD OF THE SHORT-WAVE TROUGH.  THE 12Z RAP SOUNDING
   SHOWED THE PRESENCE OF 8.0-8.5 C/KM LAPSE RATES IN THE 700-500-MB
   LAYER...ATOP A MOIST BOUNDARY LAYER WHICH WILL CONTRIBUTE TO POCKETS
   OF MODERATE INSTABILITY IN AREAS WHERE STRONGER HEATING CAN OCCUR. 
   SELY/ELY LOW-LEVEL WINDS COLOCATED WITH SWLY MIDLEVEL FLOW
   INCREASING TO 35-40 KT WILL RESULT IN MORE THAN SUFFICIENT VERTICAL
   SHEAR FOR ORGANIZED/ROTATING STORMS WITH A RISK FOR LARGE HAIL AND
   DAMAGING WINDS.

   ...SRN PLAINS THIS AFTERNOON AND EVENING...

   STEEP LAPSE RATES AND A MOIST BOUNDARY LAYER WILL ONCE AGAIN
   CONTRIBUTE TO MODERATE AFTERNOON INSTABILITY WITH MLCAPE APPROACHING
   2000-3000 J/KG.  SIMILAR TO SUNDAY...LARGE-SCALE FORCING FOR ASCENT
   WILL REMAIN NEGLIGIBLE WITH DRYLINE CIRCULATIONS BEING THE PRIMARY
   MECHANISM DRIVING ANY TSTM DEVELOPMENT.  AS A RESULT...STORM
   COVERAGE WILL LIKELY REMAIN ISOLATED WITH A RISK FOR LARGE HAIL AND
   DAMAGING WINDS PERSISTING THROUGH THIS EVENING.

   ..MEAD/MOSIER.. 05/27/2013

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