SPC AC 181252

   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0752 AM CDT SAT JUL 18 2015

   VALID 181300Z - 191200Z

   ...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS LOWER MI TO IA/NRN
   MO...

   ...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS CENTRAL HIGH PLAINS...

   ...THERE IS A MRGL RISK OF SVR TSTMS ELSEWHERE FROM NEW ENGLAND AND
   MID ATLC TO CENTRAL HIGH PLAINS...

   ...THERE IS A MRGL RISK OF SVR TSTMS PORTIONS FL PENINSULA...

   ...THERE IS A MRGL RISK OF SVR TSTMS PORTIONS SRN GREAT BASIN AND
   LOWER CO RIVER REGION...

   ...SUMMARY...
   SEVERE THUNDERSTORMS WILL BE POSSIBLE ESPECIALLY THIS AFTERNOON AND
   EVENING ACROSS PORTIONS OF THE MIDWEST AND GREAT LAKES REGION AS
   WELL AS THE CENTRAL HIGH PLAINS. A FEW STRONG STORMS MAY ALSO
   DEVELOP ACROSS PARTS OF THE MID-ATLANTIC AND NORTHEAST STATES.

   ...SYNOPSIS...
   UPPER-AIR PATTERN WILL CONTINUE TO FEATURE STG AND ZONALLY ELONGATED
   ANTICYCLONE CENTERED OVER ARKLATEX REGION...WITH RIDGING WWD ACROSS
   SERN CA AND EWD OVER GA.  TO ITS N...WELL-DEFINED MID/UPPER-LEVEL
   CYCLONE IS EVIDENT IN MOISTURE-CHANNEL IMAGERY OVER PORTIONS
   MB/SK/MT/ND...CENTERED NEAR SRN PART OF MB/SK BORDER.  THIS FEATURE
   IS FCST TO BECOME OPEN-WAVE TROUGH BY 18Z THEN MOVE ENEWD ACROSS SRN
   MB...NRN ND AND NWRN MN TO NWRN ONT BY 00Z...APCHG JAMES BAY BY END
   OF PERIOD.  TRAILING...POSITIVELY TILTED SHORTWAVE TROUGH INITIALLY
   OVER ID/NWRN NV/NRN CA SHOULD SPLIT...WITH SRN SEGMENT RETROGRADING
   SWWD ACROSS NWRN CA.  NRN PORTION SHOULD EJECT SLOWLY ENEWD OVER ID
   TOWARD WRN WY AND WEAKEN THROUGH PERIOD. 

   AT SFC...COLD FRONT NOW OVER WRN MN AND NERN-SWRN NEB IS EXPECTED TO
   REACH WRN LS...WRN IA...NWRN KS AND ERN CO BY 00Z...BECOMING AT
   LEAST TEMPORARILY QUASISTATIONARY OVER CENTRAL HIGH PLAINS.  BY
   12Z...FRONT SHOULD EXTEND FROM NRN LOWER MI ACROSS NWRN IL...NRN
   MO...AND W-CENTRAL KS.  

   ...UPPER GREAT LAKES REGION TO IA/NRN MO...
   FIRST ORDER OF BUSINESS IS COMPLEX OF TSTMS NOW CROSSING LM AND
   HEADED TOWARD LOWER MI.  GRADUAL WEAKENING TREND HAS BEEN NOTED OVER
   MUCH OF THIS COMPLEX...THOUGH ISOLATED/EMBEDDED POCKETS OF
   STG/DAMAGING GUSTS MAY STILL BE POSSIBLE FOR A FEW MORE HOURS.  REF
   SPC MESOSCALE DISCUSSION 1462 FOR NEAR-TERM DETAILS.  SOME
   RE-INTENSIFICATION OR ADDITIONAL DEVELOPMENT MAY OCCUR LATER THIS
   MORNING AS FOREGOING AIRMASS DIABATICALLY DESTABILIZES ACROSS PARTS
   OF ERN LOWER MI...IN WHICH CASE DAMAGING-GUST AND ISOLATED HAIL
   THREAT WOULD INCREASE ONCE AGAIN.  

   OUTFLOW BOUNDARY FROM THAT COMPLEX SHOULD SETTLE SWD ACROSS IL/WI
   BORDER REGION...AND ALREADY HAS BECOME QUASISTATIONARY FARTHER W
   ACROSS NWRN IA...WHERE ANOTHER/WEAKER OUTFLOW BOUNDARY FROM
   EARLIER/MORE SRN STORMS WAS DISSIPATING.  THE ONLY CONSISTENCY IN
   MOST SHORT-FUSED/CONVECTION-ALLOWING MODELS OVERNIGHT HAS BEEN THEIR
   INABILITY TO FORECAST WI/LM MCS VERY WELL...IF AT ALL.  AS
   SUCH...RESULTING CONVECTIVE PROGS INVOF OUTFLOW BOUNDARY SHOULD BE
   TREATED WITH GREAT SKEPTICISM. 

   MAIN MCS BOUNDARY SHOULD RETREAT NWD SOMEWHAT OVER NRN IA AND SRN WI
   TODAY PRIOR TO FROPA...THOUGH MESOBETA SCALE POSITIONING OF THAT AND
   OF MOST FAVORABLE RELATED CONVERGENCE/SRH/VORTICITY REMAINS
   UNCERTAIN ENOUGH ATTM TO KEEP SVR PROBABILITIES RATHER
   BROAD-BRUSHED.  WIDELY SCATTERED TO SCATTERED TSTMS SHOULD DEVELOP
   ALONG/AHEAD OF BOTH COLD FRONT AND PRIMARY OUTFLOW BOUNDARY
   TODAY...INITIALLY AS MULTICELLS AND A FEW SUPERCELLS WITH
   MULTI-HAZARD SVR THREAT BEFORE TRANSITIONING TO ONE OR TWO PRIMARY
   QLCS COMPLEXES OFFERING MAINLY WIND POTENTIAL.  AFTN/PRECONVECTIVE
   WARM SECTOR WILL BE CHARACTERIZED BY RICH...EVAPOTRANSPIRATIVELY
   AIDED MOISTURE AND STG SFC HEATING...SUPPORTING MLCAPE 3000-5000
   J/KG.  ALTHOUGH AMBIENT/EFFECTIVE SHEAR IS MOSTLY WEAK -- GENERALLY
   BELOW 30 KT -- BOTH DEEP SHEAR AND LOW-LEVEL HODOGRAPHS MAY BE
   ENHANCED INVOF OUTFLOW BOUNDARY. 

   AIR MASS FARTHER N ACROSS UPPER MI AND NRN WI NOW APPEARS UNLIKELY
   TO RECOVER SUFFICIENTLY TO SUPPORT ORGANIZED SVR RISK LATER
   TODAY...AND AS SUCH...OUTLOOK HAS BEEN DOWNGRADED FOR THOSE AREAS. 

   ...CENTRAL HIGH PLAINS...
   AS FRONT SETTLES SWD AND STALLS...POST-FRONTAL ELYS AND MOIST
   ADVECTION OVER PROGRESSIVELY HIGHER TERRAIN WILL CONTRIBUTE SEVERAL
   FAVORABLE FACTORS FOR CONVECTION THIS AFTN...INCLUDING
   1.  DIRECT UPSLOPE LIFT NEAR FRONT RANGE/FOOTHILLS...
   2.  SUFFICIENT MOISTURE TO OFFSET MIXING ENOUGH FOR MLCAPE IN
   1000-2000 J/KG RANGE 
   3. ENHANCEMENT OF DEEP SHEAR TO AROUND 40 KT...AS DETERMINED BY
   EFFECTIVE PARCELS...DESPITE WEAK BOUNDARY-LAYER SPEEDS.

   WIDELY SCATTERED TSTMS SHOULD DEVELOP NEAR WRN FRINGES OF OUTLOOK
   AREA TODAY AND MOVE ESEWD...WITH ADDITIONAL DEVELOPMENT POSSIBLE
   FARTHER ESE ACROSS ERN CO AND NWRN KS ALONG AND N OF FRONT THROUGH
   EVENING.  EARLY...RELATIVELY DISCRETE CONVECTION MAY PRODUCE
   DAMAGING GUSTS AND LARGE HAIL.  A CLUSTER OR TWO OF TSTMS SHOULD
   OFFER STG-SVR GUST POTENTIAL THIS EVENING. 

   ...CAROLINAS TO NEW ENGLAND...
   SFC TROUGH SHOULD BECOME BETTER-DEFINED THROUGH AFTN FROM ERN
   NY/NWRN NEW ENGLAND SWWD ACROSS ERN PA AND WRN CAROLINAS...AS WEAK
   SHORTWAVE TROUGH MOVES EWD NEAR CANADIAN BORDER.  FLOW ALOFT SHOULD
   INCREASE WITH NWD EXTENT...WHILE MEAN MIXING RATIOS...SFC HEATING
   AND RESULTING BUOYANCY GENERALLY STRENGTHEN SWD.  GIVEN PRESENCE OF
   WEAK MLCINH...WIDELY SCATTERED TSTMS SHOULD DEVELOP WITH RELATIVELY
   DENSE CONCENTRATION POSSIBLE NEAR TROUGH...OFFERING POTENTIAL FOR
   ISOLATED DAMAGING GUSTS. SOME HAIL ALSO MAY OCCUR...MAINLY OVER AND
   E OF HUDSON VALLEY WHERE WINDS AND COOLING ALOFT EACH ARE SOMEWHAT
   STRONGER. 

   ...FL...
   SCATTERED TSTMS SHOULD DEVELOP FROM MIDDAY THROUGH
   AFTN...PREFERENTIALLY CONCENTRATING INVOF OUTFLOW/SEA-BREEZE
   BOUNDARIES AND ESPECIALLY THEIR INTERSECTIONS AND INFLECTION POINTS
   WHERE LIFT IS LOCALLY MAXIMIZED.  THOUGH LAPSE RATES ALOFT WILL BE
   MODEST...STG HEATING OF BOUNDARY LAYER CONTAINING PW IN EXCESS OF 2
   INCHES WILL CONTRIBUTE TO DEEPLY BUOYANT THERMODYNAMIC PROFILE AND
   MLCAPE ROUGHLY 2000-2500 J/KG.  MOST INTENSE DOWNDRAFTS MAY PRODUCE
   LOCALLY DAMAGING WIND.

   ...SRN GREAT BASIN TO LOWER CO RIVER VALLEY...
   NO SUBSTANTIAL CHANGES MADE TO THIS AREA...AS SUFFICIENT LOW-LEVEL
   MOISTURE AND WELL-MIXED SUBCLOUD LAYERS STILL APPEAR POSSIBLE TO
   SUPPORT RISK FOR STG/ISOLATED SVR GUSTS IN TSTMS DEVELOPING THIS
   AFTERNOON.  MIXTURE OF PULSE AND MULTICELLULAR MODES IS
   EXPECTED...WITH MLCAPE APCHG 2000 J/KG IN SOME AREAS.

   ..EDWARDS/MARSH.. 07/18/2015

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