SPC AC 071245

   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0745 AM CDT SUN SEP 07 2014

   VALID 071300Z - 081200Z

   ...NO SVR TSTM AREAS FORECAST...

   ...SUMMARY...
   SCATTERED THUNDERSTORMS ARE LIKELY THIS AFTERNOON INTO TONIGHT
   ACROSS PARTS OF THE SOUTHEASTERN U.S....AND ACROSS THE SOUTHWESTERN
   DESERTS INTO THE CENTRAL ROCKIES.  ISOLATED STRONG/SEVERE STORMS MAY
   DEVELOP DURING THE LATE AFTERNOON AND EVENING OVER WESTERN PORTIONS
   OF NEBRASKA AND SOUTH DAKOTA AND SPREAD EASTWARD SUNDAY NIGHT.

   ...SYNOPSIS...
   UPPER-AIR PATTERN IS MOSTLY LOW IN AMPLITUDE ACROSS CONUS...AND
   DOMINATED BY
   1. ANTICYCLONE FROM DESERT SW TO MS DELTA...AND
   2. CYCLONIC FLOW ACROSS GREAT LAKES TO NEW ENGLAND.

   SERIES OF MOSTLY WEAK SHORTWAVE PERTURBATIONS WILL TRAVERSE THIS
   REGIME THROUGH PERIOD.  ONE OF THESE...NOW LOCATED OVER CENTRAL/ERN
   KS...WILL MOVE ESEWD TO KY AND WEAKEN.  ANOTHER...NOW OVER BLACK
   HILLS/NRN NEB PANHANDLE REGION...SHOULD MOVE EWD TO IA AND SRN MN
   THROUGH 12Z.  ONE MORE...NOW LOCATED OVER WRN MT...SHOULD MOVE TO
   WRN SD BY END OF PERIOD.  LARGER SHORTWAVE TROUGH -- NOW EVIDENT IN
   MOISTURE-CHANNEL IMAGERY OFFSHORE CA NEAR 130W...WILL PIVOT SLOWLY
   TOWARD NRN CA COAST AND CONTRACT...RESULTING IN SMALL/CLOSED 500-MB
   LOW NEAR CAPE MENDOCINO BY 12Z.  STG SHORTWAVE TROUGH NOW OVER SERN
   AK WILL DIG SEWD ACROSS BC.  MEANWHILE...OVER SERN
   CONUS...WEAK/DEEP-LAYER AREA OF LOW HEIGHTS AND PRESSURE OVER NRN
   FL/SRN GA REGION IS EXPECTED TO SHIFT SLOWLY NEWD ACROSS SRN/ERN SC.

   AT SFC...11Z ANALYSIS SHOWED COLD FRONT FROM OFFSHORE NANTUCKET SWWD
   OVER HAMPTON ROADS AREA...NWRN NC...CENTRAL AL...S-CENTRAL TX...AND
   NRN CHIHUAHUA.  HAVING OUTRUN ITS MID/UPPER-LEVEL SUPPORT...AND
   RELYING PRIMARILY ON CONVECTIVE PRECIP FOR REMAINING
   PROGRESSION/REINFORCEMENT OF ITS BAROCLINICITY...THIS FRONTAL ZONE
   SHOULD CONTINUE TO DECELERATE AND WEAKEN THROUGHOUT DAY-1.  BY
   00Z...QUASISTATIONARY FRONT SHOULD EXTEND FROM ERN GA/SC LOW SWWD
   ACROSS SRN AL TO S-CENTRAL TX...WHILE MOVING SLOWLY NWD AS WARM
   FRONT OVER FAR W TX AND BIG BEND AREA.  AS LEE TROUGHING BECOMES
   MORE PRONOUNCED OVER CENTRAL/NRN HIGH PLAINS DURING AFTN AND
   OVERNIGHT...FRONTOLYSIS WILL CONTINUE OVER W TX AND NM...WHILE
   ANOTHER COLD FRONT APCHS NRN MT BORDER BY 12Z.

   ...CENTRAL/NRN PLAINS...
   STRENGTHENING SFC LEE TROUGHING AND DEEP-LAYER FLOW ARE EXPECTED
   OVER THIS REGION TODAY...RELATED TO TIGHTENING HEIGHT GRADIENTS
   AHEAD OF AK-BC SHORTWAVE TROUGH. RELATED LOW-LEVEL WAA...INCLUDING
   40-50-KT NOCTURNAL/SLY LLJ...WILL SUPPORT CONVECTIVE POTENTIAL OVER
   THIS REGION.  TWO PRIMARY AND PERHAPS SPATIALLY OVERLAPPING REGIMES
   WILL SUPPORT TSTM POTENTIAL THROUGH PERIOD.  IN BOTH OF
   THESE...GREATER UNCONDITIONAL SVR RISK IS PRECLUDED BY CONCERNS OVER
   SUFFICIENT COVERAGE OF STG-SVR TSTMS AND LACK OF SUBSTANTIAL
   LARGE-SCALE LIFT.

   1. AFTN SFC DIABATIC HEATING BEHIND MORNING PERTURBATION ALOFT...AND
   RESULTANT WEAKENING OF INITIALLY STG EML-RELATED CAPPING EVIDENT IN
   REGIONAL/12Z RAOBS.  THIS WILL RENDER 8-9 DEG C/KM LAPSE RATES IN
   SFC-500-MB LAYER BY 21-00Z TIME FRAME.  MOIST ADVECTION SHOULD
   OFFSET VERTICAL MIXING ENOUGH TO MAINTAIN POCKETS OF
   RESIDUAL/SUPPORTIVE SFC MOISTURE...WITH DEW POINTS GENERALLY IN MID
   40S TO LOW 50S F SURROUNDING NARROW CORRIDOR OF LOW-MID 50S.  NET
   RESULT SHOULD BE 1000-2500 J/KG MLCAPE AMIDST 25-35 KT
   EFFECTIVE-SHEAR MAGNITUDES.  HOWEVER...STG MID-UPPER WINDS WILL LEAD
   TO FAVORABLE CLOUD-LAYER SHEAR...AND VENTING OF UPDRAFTS.  WIDELY
   SCATTERED TSTMS...MOSTLY MULTICELLULAR BUT WITH ISOLATED
   SUPERCELLS...SHOULD RESULT.  ISOLATED DAMAGING GUSTS AND SVR HAIL
   ARE POSSIBLE.

   2. LOW-LEVEL WAA AND MOISTURE TRANSPORT ABOVE SFC WILL BOOST
   THETAE...DECREASING MUCINH AND LEADING TO ISENTROPIC LIFT OF PARCELS
   TO LFC THIS EVENING AND OVERNIGHT.  FCST SOUNDINGS SUGGEST BROAD
   AREA OF ELEVATED MUCAPE EXCEEDING 2000 J/KG MAY DEVELOP...JUXTAPOSED
   WITH 40-50 KT EFFECTIVE SHEAR.  THIS INDICATES CONDITIONAL SVR-HAIL
   RISK FOR ANY SUSTAINED CONVECTION.
   WHILE SOME AFTN/EARLY EVENING TSTMS MAY SURVIVE EWD INTO THIS REGIME
   AND BECOME ELEVATED...CONVECTION-ALLOWING GUIDANCE REASONABLY
   INDICATES TSTMS WILL DEVELOP ANEW.

   ..EDWARDS/JIRAK.. 09/07/2014

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