May 19, 2014 1300 UTC Day 1 Convective Outlook

DAY 1 CONVECTIVE OUTLOOK  

   NWS STORM PREDICTION CENTER NORMAN OK
   0623 AM CDT MON MAY 19 2014

   VALID 191300Z - 201200Z

   ...THERE IS A SLGT RISK OF SVR TSTMS FROM EXTREME SERN WY ACROSS WRN
   NEB...

   ...SUMMARY...
   ISOLATED TO SCATTERED STRONG TO SEVERE THUNDERSTORMS WITH HAIL WILL
   BE POSSIBLE ACROSS THE CENTRAL HIGH PLAINS TO UPPER MIDWEST MONDAY
   AFTERNOON AND EVENING.

   ...SYNOPSIS...
   A LARGE-SCALE PATTERN CHANGE WILL BEGIN OVER THE CONUS TODAY AS AN
   UPPER LOW TRACKS INLAND ACROSS COASTAL NRN CA AND DOWNSTREAM RIDGING
   BUILDS FROM TX TO THE ERN GREAT LAKES. EXTENSIVE LOWER STATIC
   STABILITY ASSOCIATED WITH BROAD TROUGHING ACROSS THE NORTHWEST AND
   NORTHERN ROCKIES WILL CONTRIBUTE TO WIDESPREAD DIURNAL CONVECTIVE
   SHOWERS AND A FEW TSTMS AMIDST WEAK INSTABILITY AND WEAK TO MODEST
   SHEAR. MORE ROBUST DEEP CONVECTION WILL BE POSSIBLE OVER PARTS OF
   THE NRN/CNTRL PLAINS AND UPPER MS VALLEY. IN THESE AREAS...WEAK SFC
   LOW AND COLD FRONT...AS WELL AS A PERSISTENT AND STRONG SLY
   LOW-LEVEL JET...WILL PROMOTE BOUTS OF ISOLATED TO SCATTERED STRONG
   TO SEVERE TSTMS.

   ...NRN/CNTRL PLAINS...
   A BROKEN ARC OF TSTMS IS EVIDENT ON RADAR THIS MORNING FROM THE
   ND/MN BORDER SOUTH TO MID MISSOURI RIVER VALLEY. THIS ACTIVITY WAS
   BEING SUSTAINED BY ISENTROPIC ASCENT ON THE NOSE OF 60KT LOW-LEVEL
   JET IN COMBINATION WITH FAVORABLE LARGE-SCALE ASCENT ACCOMPANYING A
   SHORTWAVE TROUGH SPREADING NEWD ACROSS THE NRN PLAINS. WHILE THIS
   CONVECTION WILL REMAIN ROOTED ABOVE A STABLE BOUNDARY LAYER...ITS
   PROXIMITY TO MUCAPE AROUND 1000 J/KG AND POCKETS OF STRONGER
   EFFECTIVE SHEAR SUGGEST ONE OR TWO SEVERE HAIL EVENTS REMAIN
   POSSIBLE UNTIL THE STORMS DRIFT ENEWD AND AWAY FROM STRONGER
   INSTABILITY SITUATED ACROSS THE PLAINS.

   IN THE WAKE OF THIS LEADING SHORTWAVE TROUGH AND ELEVATED MORNING
   CONVECTION...A BROAD ZONE OF SFC LOW PRESSURE WILL PERSIST ACROSS
   THE NRN/CNTRL PLAINS AS A WEAK COLD FRONT SETTLES SEWD FROM WRN SD
   AND ERN WY INTO WRN AND CNTRL SECTIONS OF NEB DURING THE DAY. A SLGT
   RISK HAS BEEN RE-INTRODUCED OVER NEB WITH THIS OTLK. THIS DECISION
   IS BASED ON THE CONDITIONAL PROBABILITY THAT POST-FRONTAL UPSLOPE
   FLOW ACROSS WRN NEB/ERN WY...IN COMBINATION WITH SUBTLE BUT
   PERSISTENT FORCING NEAR SFC FRONT AND NORTH OF TRIPLE-POINT
   LOW...WILL BE ADEQUATE FOR AT LEAST ISOLATED TSTM DEVELOPMENT BY
   LATE AFTERNOON INTO EARLY EVENING. WHILE MOST SYNOPTIC-SCALE MODELS
   ONLY HINT AT THE PROSPECT FOR DEEP CONVECTIVE DEVELOPMENT ACROSS
   WY/NEB BORDER DURING THIS TIME...STORM-SCALE/CONVECTION-ALLOWING
   GUIDANCE /SSEO AND AFWA ENSEMBLES/ EXPLICITLY PREDICT AT LEAST A
   COUPLE OF WELL-ORGANIZED AND PERSISTENT UPDRAFTS DEVELOPING ACROSS
   WRN/CNTRL NEB THROUGH THE EVENING HOURS.

   GIVEN THE ABOVE SCENARIO...ANY STORMS SPREADING EAST FROM NEB PNHDL
   MAY ENCOUNTER AN INCREASINGLY SUPPORTIVE THERMODYNAMIC AND KINEMATIC
   ENVIRONMENT FOR SUSTAINED UPDRAFT ROTATION AND POSSIBLE LARGE TO
   VERY LARGE HAIL. WHILE STRENGTH OF CAPPING/INHIBITION WITH EWD
   EXTENT MAY LIMIT THE NUMBER OF STORMS...THE CONDITIONAL THREAT
   APPEARS HIGH ENOUGH TO WARRANT A 15 PERCENT PROBABILITY OF SEVERE
   HAIL AND A 10 PERCENT PROBABILITY OF SIGNIFICANT /AT LEAST 2 INCH/
   HAIL. TORNADO POTENTIAL WITH ANY SUPERCELLS APPEARS LIMITED BASED ON
   WEAK BOUNDARY LAYER FLOW AND RELATIVELY HIGH CLOUD BASES. SIMILAR TO
   LAST NIGHT/THIS MORNING...PROSPECTS FOR OVERNIGHT/ELEVATED STORMS
   WITH HAIL MAY INCREASE THROUGH TONIGHT AND INTO TUESDAY MORNING AS
   NOCTURNAL LOW-LEVEL JET AND ISENTROPIC ASCENT AGAIN STRENGTHEN ON
   THE EDGE OF THE PLAINS CAPPING INVERSION AND ACT TO SUSTAIN ELEVATED
   CONVECTION FROM THE MID MISSOURI VALLEY TO UPPER MS VALLEY.