Sep 21, 2014 1300 UTC Day 1 Convective Outlook

DAY 1 CONVECTIVE OUTLOOK  

   NWS STORM PREDICTION CENTER NORMAN OK
   0753 AM CDT SUN SEP 21 2014

   VALID 211300Z - 221200Z

   ...NO SVR TSTM AREAS FORECAST...

   ...SUMMARY...
   SCATTERED SHOWERS AND THUNDERSTORMS -- A FEW WITH GUSTS APPROACHING
   SEVERE LEVELS -- WILL BE POSSIBLE FROM THE LOWER GREAT LAKES ACROSS
   THE CENTRAL APPALACHIANS TO THE MID SOUTH.  SCATTERED THUNDERSTORMS
   ARE ALSO EXPECTED ACROSS PARTS OF THE SOUTHWEST AND GREAT
   BASIN...WITH ISOLATED AND MARGINAL SEVERE STORMS POSSIBLE MAINLY
   OVER UTAH THIS AFTERNOON AND EVENING.

   ...SYNOPSIS...
   IN MID-UPPER LEVELS...GENERAL AMPLIFICATION OF PROGRESSIVE SYNOPTIC
   PATTERN IS FCST THROUGH PERIOD.  LEADING PORTION OF STG SHORTWAVE
   TROUGH NOW OVER LOWER MI AND LM IS FCST TO PIVOT EWD ACROSS ERN/SRN
   ONT THROUGH PERIOD...REACHING SRN QUE AND HUDSON VALLEY REGION BY
   12Z.  BY THAT TIME...TRAILING VORTICITY BANNER SHOULD EXTEND SWWD
   ACROSS WV AND TN...CONTRIBUTING TO LARGER-SCALE TROUGH
   AMPLIFICATION.  LEADING/SRN-STREAM PERTURBATION -- NOW EVIDENT IN
   MOISTURE-CHANNEL IMAGERY OVER COASTAL CAROLINAS -- WILL EJECT NEWD
   ACROSS ATLC TOWARD NOVA SCOTIA. 

   FARTHER W...MID-UPPER-LEVEL CYCLONE NOW OVER CENTRAL CA AND ADJACENT
   SIERRAS WILL MOVE NEWD ACROSS CENTRAL/NRN NV...REACHING SRN ID/NERN
   WY AND DEVOLVING INTO OPEN-WAVE TROUGH NEAR END OF PERIOD.  

   AT SFC...11Z ANALYSIS SHOWED LOW OVER LH WITH COLD FRONT SWWD ACROSS
   CENTRAL INDIANA...SWRN MO...SERN KS...NWRN OK AND ERN NM.  WARM
   FRONT WAS DRAWN FROM LOW SSWWD OVER CENTRAL OH AND NERN/CENTRAL KY. 
   LOW SHOULD EJECT NEWD OVER ST. LAWRENCE VALLEY TODAY...WITH COLD
   FRONT REACHING ERN PA...WRN VA...NRN MS...AND N TX BY 00Z.  BY
   12Z...FRONT SHOULD MOVE OFFSHORE MID ATLC AND REACH COASTAL
   CAROLINAS...EXTENDING SWWD ACROSS CENTRAL/SRN PORTIONS OF MS AND TX.

   ...NERN CONUS TO MID SOUTH...
   ONE OR TWO NARROW BANDS OF CONVECTION WITH EMBEDDED TSTMS SHOULD
   DEVELOP THROUGH EARLY-MID AFTN...POSSIBLY INCLUDING EWD
   SHIFT/EXTENSION OF CONVECTION NOW EVIDENT NEAR BUF-PKB LINE.  AT
   LEAST ISOLATED GUSTS APCHG SVR LIMITS MAY OCCUR...AND POTENTIAL
   EXISTS FOR SUB-SVR GUSTS...BELOW 50 KT...TO PRODUCE MINOR WIND
   DAMAGE SUCH AS DOWNED LIMBS/TREES OVER SOME AREAS. 

   NARROW CORRIDOR OF MID-UPPER-60S SFC DEW POINTS IS EVIDENT BETWEEN
   COLD AND WARM FRONTS ATTM...WITH LOWER 60S FARTHER E TO  WRN PARTS
   OF NY/PA/WV.  THIS WILL ACT IN TANDEM WITH SPORADIC DIURNAL HEATING
   UNDER VARIABLE CLOUD COVER TO YIELD 200-500 J/KG PREFRONTAL MLCAPE. 
   BUOYANCY WILL INCREASE WITH SWWD EXTENT TOWARD MID SOUTH AS
   DEEP-LAYER FLOW DIMINISHES...AND FROM ABOUT OH RIVER NWD...MOST
   FAVORABLE LOW-LEVEL FORCING ULTIMATELY WILL OUTPACE EWD SHIFT OF
   RICHEST LOW-LEVEL MOIST PLUME. 

   FLOW ALOFT WILL BE LARGELY PARALLEL TO COLD FRONT AND ANY PREFRONTAL
   CONFLUENCE/CONVERGENCE LINES UPON WHICH TSTMS MAY
   DEVELOP...INDICATING PREDOMINANTLY LINEAR MODE.  THOUGH MLCINH WILL
   REMAIN WEAK...LACK OF MORE ROBUST PRECONVECTIVE SFC WINDS SHOULD
   LIMIT CONVERGENCE.  THESE OFFSETTING FACTORS...AND LACK OF MORE
   ROBUST INSTABILITY OVER NRN AREAS...PRECLUDE CATEGORICAL UPGRADE FOR
   NOW. 

   ...UT AND VICINITY...
   SCATTERED TSTMS ARE EXPECTED TO DEVELOP THROUGH EVENING OVER AREAS
   FROM SRN NV AND NRN AZ ACROSS MUCH OF UT.  ISOLATED DAMAGING GUSTS
   ARE POSSIBLE.

   EXTENSIVE/ONGOING AREA OF CLOUDS/PRECIP AND EMBEDDED SHOWERS/TSTMS
   WILL LEAD TO FRAGMENTED...MUTED AND SLOWLY PACED DIURNAL HEATING
   ACROSS THIS AREA.  MLCAPE ULTIMATELY MAY REACH 300-800 J/KG IN
   POCKETS BY MID-LATE AFTN...WHILE DEEP-LAYER FLOW INCREASE WITH APCH
   OF CA VORTEX ALOFT.  ALTHOUGH CYCLONE WILL BE WEAKENING...RELATED
   DCVA SHOULD CONTRIBUTE SUBTLE COOLING/DESTABILIZATION ALOFT IN
   SUPPORT OF EPISODIC CONVECTIVE POTENTIAL.

   ..EDWARDS/MARSH.. 09/21/2014