SPC AC 171956

   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0256 PM CDT THU OCT 17 2013

   VALID 172000Z - 181200Z

   ...NO SVR TSTM AREAS FORECAST...

   ...DISCUSSION...
   NO SUBSTANTIAL CHANGES ARE BEING MADE TO THE PRIOR FORECAST
   ATTM...ASIDE FROM SHRINKING MOST THUNDER AREAS.  A NARROW BAND OF
   LOW-TOPPED CONVECTION IS ONGOING ATTM FROM WRN PA SSWWD INTO SRN
   WV/FAR WRN VA...AND THE LINE WILL CONTINUE SHIFTING EWD WITH TIME AS
   THE FRONT AND ASSOCIATED UPPER VORT MAX ADVANCE.  WHILE
   DESTABILIZATION AHEAD OF THE FRONTAL CONVECTION HAS BEEN
   MINIMAL...STRENGTH OF FLOW ALOFT MAY STILL PERMIT A FEW STRONGER
   GUSTS TO OCCUR LOCALLY AS THE CONVECTION PASSES FROM W-E THROUGH THE
   END OF THE PERIOD.

   ..GOSS.. 10/17/2013

   .PREV DISCUSSION... /ISSUED 1109 AM CDT THU OCT 17 2013/

   ...SYNOPSIS...

   A BROAD CYCLONIC FLOW REGIME WILL BE MAINTAINED OVER THE CONUS WITH
   A BELT OF STRONG MID AND UPPER-LEVEL FLOW STRETCHING FROM THE
   CNTRL/SRN PLAINS THROUGH THE NORTHEAST AND MID ATLANTIC STATES. 
   EMBEDDED WITHIN THIS HIGHER MOMENTUM AIR STREAM...A SHORT-WAVE
   TROUGH OVER THE MIDWEST WILL TRANSLATE NEWD INTO THE ST. LAWRENCE
   VALLEY BY 18/12Z.  OTHER MORE PROMINENT VORTICITY MAXIMA WILL TRACK
   FROM THE NRN PLAINS INTO UPPER GREAT LAKES...AND FROM THE NRN
   INTER-MOUNTAIN REGION TO CNTRL/SRN ROCKIES DURING THE D1 PERIOD.

   IN THE LOW LEVELS...A SURFACE CYCLONE ASSOCIATED WITH THE MIDWEST
   SHORT-WAVE TROUGH WILL DEEPEN WHILE DEVELOPING NEWD FROM THE CNTRL
   APPALACHIANS THROUGH CNTRL PA LATE THIS AFTERNOON BEFORE REACHING
   MAINE EARLY FRI.  MEANWHILE...A TRAILING COLD FRONT WILL ADVANCE
   EWD/SEWD TO OFF THE MID ATLANTIC COAST.

   ...CNTRL APPALACHIANS TO NEW ENGLAND THIS AFTERNOON INTO TONIGHT...

   BOTH FORCING FOR ASCENT AND VERTICAL SHEAR WILL INCREASE WITH THE
   APPROACH OF THE MIDWEST/OH VALLEY SHORT-WAVE TROUGH.  HOWEVER...
   MORNING VISIBLE SATELLITE IMAGERY INDICATES AN EXPANSIVE CLOUD
   SHIELD ATTENDING THIS SYSTEM WHICH WILL PROGRESSIVELY OVERSPREAD THE
   REGION TODAY...LIMITING THE DEGREE OF AIR MASS DESTABILIZATION AHEAD
   OF THE COLD FRONT.

   LATEST CONVECTION-ALLOWING MODEL GUIDANCE SUGGESTS THAT A LOW-TOPPED
   CONVECTIVE BAND --WITH A FEW EMBEDDED TSTMS-- WILL BECOME
   INCREASINGLY POSSIBLE BY LATE AFTERNOON OR EARLY EVENING FROM
   CNTRL/ERN PA INTO NRN VA AS THE STRONGER FORCING FOR ASCENT/DCVA
   ASSOCIATED WITH THE SHORT-WAVE TROUGH LINKS WITH THE FRONTAL UPLIFT.
   SHOULD SUFFICIENT DESTABILIZATION OCCUR TO SUPPORT SURFACE-BASED
   STORM DEVELOPMENT...THE DOWNWARD MOMENTUM TRANSFER OF AN
   INCREASINGLY STRONG TROPOSPHERIC WIND FIELD MAY PROMOTE LOCALLY
   STRONG WIND GUSTS WITH THE CONVECTIVE BAND.

   ...CNTRL/ERN GULF COAST THIS AFTERNOON...

   ISOLATED TO WIDELY SCATTERED TSTMS WILL BE POSSIBLE THIS AFTERNOON
   ALONG AND AHEAD OF THE COLD FRONT WHERE SEASONABLY MOIST CONDITIONS
   WILL YIELD MLCAPE OF 500-1000 J/KG.  WHILE A STRONG STORM OR TWO IS
   POSSIBLE...MARGINAL AMOUNTS OF INSTABILITY AND VERTICAL SHEAR WILL
   PRECLUDE SEVERE WEATHER POTENTIAL.

   ...CNTRL/SRN PLAINS TONIGHT...

   THE SEWD PROGRESSION OF A SHORT-WAVE TROUGH THROUGH THE CNTRL PLAINS
   WILL CONTRIBUTE TO THE ENHANCEMENT OF A NOCTURNAL LLJ AND THE
   POLEWARD RETURN OF A PARTIALLY MODIFIED AIR MASS THROUGH THE SRN
   HIGH PLAINS.  THIS MOISTURE RETURN WILL OCCUR BENEATH A PLUME OF
   STEEP MIDLEVEL LAPSE RATES...BOOSTING MUCAPE TO 500-1000 J/KG. 
   ISOLATED TO WIDELY SCATTERED ELEVATED TSTMS WILL BECOME INCREASINGLY
   POSSIBLE WITHIN THIS REGIME IN THE 18/09-12Z TIME FRAME AS FORCING
   FOR ASCENT IS ENHANCED BY WAA/ISENTROPIC AT THE TERMINUS OF THE LLJ.
   NO SEVERE WEATHER IS EXPECTED.

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