Categorical Graphic
Probabilistic Tornado Graphic
Probabilistic Damaging Wind Graphic
Probabilistic Large Hail Graphic

   SPC AC 120600
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0100 AM CDT SUN APR 12 2009
   
   VALID 121200Z - 131200Z
   
   ...THERE IS A MDT RISK OF SVR TSTMS ACROSS MUCH OF SRN LA AND
   ADJACENT SWRN MS...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS A LARGE PORTION OF THE S
   CENTRAL CONUS...
   
   ...SYNOPSIS...
   A LARGE UPPER LOW IS FORECAST TO SHIFT ENEWD FROM THE SRN HIGH
   PLAINS ACROSS OK THROUGH THE DAY...AND INTO SERN KS/WRN MO LATE IN
   THE PERIOD.  WHILE THIS WILL BE THE PRIMARY FEATURE WITH REGARD TO 
   SEVERE CONVECTION...TWO OTHER SYSTEMS -- ONE SLOWLY EXITING NEW
   ENGLAND AND ANOTHER APPROACHING THE PAC NW THROUGH THE SECOND HALF
   OF THE PERIOD -- WILL ALSO AFFECT THE U.S. THIS PERIOD.
   
   AT THE SURFACE...A DEEPENING LOW CROSSING THE CANADIAN MARITIMES
   ASSOCIATED WITH THE NERN U.S. UPPER SYSTEM WILL RESULT IN WINDY 
   CONDITIONS ACROSS NEW ENGLAND...WHILE A COLD FRONT SHOULD CROSS THE
   PAC NW AHEAD OF THE NWRN UPPER SYSTEM.  
   
   OVER THE S CENTRAL CONUS...A SURFACE LOW INITIALLY OVER WRN N TX
   INVOF THE UPPER LOW SHOULD MOVE SLOWLY EWD/ENEWD...WHILE A WEAK
   SECONDARY CYCLONE LIKELY EVOLVES INVOF E TX DURING THE AFTERNOON AND
   THEN MOVE ENEWD ACROSS AR AND INTO THE MID MS VALLEY REGION.  BY THE
   END OF THE PERIOD...THE PRIMARY COLD FRONT SHOULD EXTEND FROM THIS
   WEAK/TRIPLE POINT LOW SWWD ALONG THE LOWER MS VALLEY AND THEN WSWWD
   ACROSS ERN/SRN TX.
   
   ...E TX EWD ACROSS THE LOWER MS VALLEY...
   WIDESPREAD CONVECTION -- AND SOME ASSOCIATED SEVERE THREAT -- WILL
   BE SPREADING ENEWD ACROSS TX AT THE START OF THE PERIOD...AS UPPER
   HEIGHT FALLS CONTINUE SPREADING EWD ACROSS THE S CENTRAL CONUS AHEAD
   OF THE MAIN UPPER LOW.  WIDESPREAD NATURE OF THE
   CLOUDS/PRECIPITATION SHOULD LIMIT HEATING ACROSS FAR NERN TX/ERN
   OK/AR.  HOWEVER...LIMITED HEATING ALONG AN EXPECTED SRN FRINGE OF
   THE MORE WIDESPREAD PRECIPITATION COMBINED WITH NWD ADVECTION OF
   UPPER 60S DEWPOINTS INTO SOUTHEAST TX/LA SHOULD YIELD MODEST
   DESTABILIZATION THROUGH THE DAY.  WITH CONTINUED HEIGHT FALLS AHEAD
   OF THE UPPER SYSTEM...CONTINUED REDEVELOPMENT OF STORMS ACROSS SERN
   TX/LA THROUGH THE DAY...AND EVENTUALLY INTO SRN MS...IS ANTICIPATED
   -- ALONG THE SRN FLANK OF THE HEAVIER PRECIPITATION AREA.
   
   SELY BOUNDARY-LAYER FLOW IS FORECAST TO PERSIST ACROSS THIS
   REGION...BENEATH INCREASINGLY-STRONG/DIFFLUENT MID-LEVEL SWLYS.  THE
   RAPID VEERING/INCREASING FLOW WITH HEIGHT WILL YIELD SHEAR
   SUPPORTIVE OF STRONGLY-ROTATING STORMS.  IF A SRN EDGE OF THE
   BROADER AREA OF PRECIPITATION DOES INDEED EXIST ACROSS SERN TX AND
   PARTICULARLY LA DURING THE DAY...MORE ISOLATED/CELLULAR STORM MODE
   WOULD SUGGEST A POTENTIAL FOR SEVERAL LONG-LIVED/TORNADO-PRODUCING
   STORMS.  WHILE THIS SCENARIO COULD BE FOULED BY A MORE WIDESPREAD
   DEVELOPMENT OF CONVECTION INTO THE NWRN GULF...WILL NONETHELESS
   INTRODUCE A MODERATE RISK ACROSS LA/SWRN MS TO COVER THE THIS
   ENHANCED TORNADO POTENTIAL.  OTHERWISE...HAIL AND DAMAGING WINDS ARE
   ALSO ANTICIPATED AS STORMS SPREAD ACROSS THIS REGION. 
   OVERNIGHT...CONVECTION SHOULD CONTINUE EWD ACROSS LA/SRN MS...WITH
   SEVERE/ISOLATED TORNADO THREAT PERHAPS EXTENDING INTO WRN AL LATE.
   
   ...N TX/SRN OK...
   BEHIND THE INITIAL/EXPANSIVE AREA OF RAIN/THUNDERSTORMS...CONVECTIVE
   REDEVELOPMENT IS FORECAST AS MODEST DAYTIME HEATING IS ANTICIPATED
   BENEATH THE MID-LEVEL COLD POOL...YIELDING 500 TO 1000 J/KG
   MIXED-LAYER CAPE BY LATE AFTERNOON.  WITH AMPLE SHEAR ACROSS THE RED
   RIVER VALLEY AREA SE OF THE UPPER LOW CENTER...A FEW
   STRONGER/ORGANIZED STORMS MAY PRODUCE HAIL AND/OR LOCALLY-DAMAGING
   WINDS.  STORMS -- BEING DRIVEN PRIMARILY BY DIURNAL HEATING --
   SHOULD DIMINISH THROUGH THE EVENING.
   
   ..GOSS.. 04/12/2009
   
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   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z