SPC AC 171959

   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0159 PM CST TUE NOV 17 2015

   VALID 172000Z - 181200Z

   ...THERE IS AN ENH RISK OF SVR TSTMS OVER PORTIONS OF AR AND LA INTO
   WESTERN MS...

   ...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE ENH RISK FROM
   SOUTHEASTERN TX AND EASTERN PORTIONS OF THE OZARK PLATEAU TO THE
   CENTRAL GULF COAST...

   ...THERE IS A MRGL RISK OF SVR TSTMS SURROUNDING THE SLGT RISK OVER
   THE SAME GENERAL AREAS...

   ...SUMMARY...
   A SQUALL LINE CAPABLE OF DAMAGING STRAIGHT-LINE WINDS AND ISOLATED
   TORNADOES WILL MOVE ACROSS THE LOWER MISSISSIPPI VALLEY AND
   NORTHWEST GULF COAST.  THE AREA OF GREATEST CONCERN FOR MORE
   WIDESPREAD DAMAGING WINDS AND A FEW TORNADOES IS OVER PARTS OF
   ARKANSAS AND LOUISIANA AND WESTERN MISSISSIPPI THIS AFTERNOON
   THROUGH THIS EVENING.

   ...OZARK PLATEAU AND EAST TX TO CENTRAL GULF COAST STATES...
   THE FORECAST REMAINS ON TRACK ACROSS THE OZARK PLATEAU TO THE
   NORTHWEST GULF COAST AND EASTWARD TO THE CENTRAL GULF COAST STATES
   THIS AFTERNOON THROUGH TONIGHT.  THE SEVERE WEATHER THREAT WILL
   REMAIN ATTENDANT TO THE EASTWARD-MOVING PRE-FRONTAL SQUALL
   LINE...WHICH AT 1930Z EXTENDED FROM CENTRAL AR SOUTHWESTWARD THROUGH
   NORTHERN LA TO THE UPPER TX COAST.  THE POLEWARD MOISTURE RETURN HAS
   RESULTED IN SURFACE DEW POINTS AROUND 70 F IN SOUTHEAST AR AND
   WEST-CENTRAL MS COMBINED WITH FILTERED SUNSHINE TO AID IN MUCAPE OF
   1000-1500 J/KG ACROSS MUCH OF THE ENH RISK AREA AND SOUTHERN HALF OF
   THE SLGT RISK AREA.  ONGOING STABILIZATION WITH THE PASSAGE OF THE
   SQUALL LINE HAS RESULTED IN A DIMINISHED SEVERE WEATHER THREAT WITH
   WESTWARD EXTENT.  THIS TREND WILL PERSIST WITH THE PASSAGE OF THE
   LINE OF STORMS...AND HAS BEEN INDICATED BY TRIMMING THE WESTERN
   PORTIONS OF THE SEVERE PROBABILITIES AND CATEGORICAL RISK AREAS WITH
   THIS OUTLOOK ISSUANCE.

   ...ELSEWHERE...
   THE GENERAL TSTM LINE HAS BEEN ADJUSTED FOR LIGHTNING TRENDS ALONG
   THE PRIMARY COLD FRONT AS IT ADVANCES ACROSS CENTRAL TX...AND ALSO
   FOR RECENT STRIKES ACROSS SOUTHEAST CO.

   ..PETERS.. 11/17/2015

   .PREV DISCUSSION... /ISSUED 1026 AM CST TUE NOV 17 2015/

   ...SYNOPSIS...

   AN INTENSE MID-LEVEL LOW OVER THE SRN HIGH PLAINS WILL PIVOT NEWD
   INTO ERN PORTIONS OF NEB AND KS WHILE AN ATTENDANT 100+ KT JET
   STREAK AT 500 MB ADVANCES FROM THE CNTRL AND SRN HIGH PLAINS INTO
   THE MS VALLEY.  AT THE SURFACE...A PACIFIC FRONT PRESENTLY
   STRETCHING FROM AN AREA OF LOW PRESSURE OVER CNTRL KS SSEWD INTO
   CNTRL TX WILL PROGRESS EWD TOWARD THE MIDDLE AND LOWER MS VALLEYS. 
   MEANWHILE THE KS SURFACE LOW WILL FURTHER DEEPEN AND SUBSEQUENTLY
   UNDERGO OCCLUSION AS IT ACCELERATES NNEWD INTO THE UPPER MS VALLEY. 


   ...OZARK PLATEAU INTO ERN TX AND EWD INTO THE CNTRL GULF STATES...

   A WIDESPREAD AREA OF PRE-FRONTAL SHOWERS AND THUNDERSTORMS ARE
   ONGOING AS OF MID MORNING FROM THE OZARK PLATEAU INTO ERN
   TX...DRIVEN HEAT AND MOISTURE FLUXES ALONG A 50-60+ KT SLY LLJ AND
   THE LEADING EDGE OF STRONGER HEIGHT FALLS/DCVA PRECEDING THE SRN
   PLAINS UPPER LOW.  THESE SAME FORCING MECHANISMS WILL GRADUALLY
   SHIFT EWD TOWARD THE MS VALLEY TODAY...COMBINING WITH THE CONTINUED
   INFLUX OF A VERY MOIST AIR MASS FROM OFF THE GULF OF MEXICO AND
   FILTERED SUNSHINE TO SUPPORT THE GRADUAL INTENSIFICATION OF STORMS
   ALONG THE LEADING EDGE OF THE WIDESPREAD MORNING CONVECTION.  GIVEN
   THE CO-LOCATION OF A MOIST AND MODERATELY UNSTABLE AIR MASS WITH
   STRONG LOW-LEVEL AND DEEP-LAYER SHEAR...THE POTENTIAL WILL EXIST FOR
   EMBEDDED SUPERCELL AND LEWP STRUCTURES WITH AN ASSOCIATED RISK FOR
   DAMAGING STRAIGHT-LINE WINDS AND A FEW TORNADOES.  

   ADDITIONALLY...VARIOUS CONVECTION-ALLOWING MODEL SOLUTIONS SUGGEST
   THE POTENTIAL FOR ADDITIONAL BANDS OF SEMI-DISCRETE STORMS FORMING
   THIS AFTERNOON ALONG CONFLUENCE ZONES OVER ERN PORTIONS OF LA AND AR
   INTO WRN MS...AHEAD OF THE MAIN QLCS.  SHOULD THIS SCENARIO UNFOLD
   AS FORECAST...A MORE SUBSTANTIAL TORNADO THREAT WOULD EXIST AND THIS
   IS ADDRESSED WITH THE 10 PERCENT TORNADO PROBABILITY CONTOUR.

   EXPECT THE EVOLVING QLCS TO ADVANCE EWD THROUGH THE LOWER MS VALLEY
   LATER THIS AFTERNOON INTO EVENING BEFORE REACHING ERN MS AND WRN AL
   LATER TONIGHT INTO EARLY WEDNESDAY.  THE VERY INTENSE WIND FIELDS
   COUPLED WITH SUFFICIENT INSTABILITY WILL MAINTAIN THE RISK FOR
   ISOLATED OCCURRENCES OF DAMAGING WINDS AND PERHAPS A BRIEF TORNADO
   WITH THE PASSAGE OF THE SQUALL LINE.

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