Categorical Graphic
Probabilistic Tornado Graphic
Probability of a tornado within 25 miles of a point. Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Probabilistic Damaging Wind Graphic
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point. Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
Probabilistic Large Hail Graphic
Probability of hail 1" or larger within 25 miles of a point. Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point.

   SPC AC 181959
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0259 PM CDT SUN SEP 18 2011
   
   VALID 182000Z - 191200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS FROM CENTRAL TX NEWD INTO THE
   WRN OZARKS...
   
   ...CENTRAL TX TO PARTS OF SRN MO THIS AFTERNOON/EVENING...
   MINOR ADJUSTMENTS HAVE BEEN MADE TO THE SLIGHT RISK AND SEVERE
   WEATHER PROBABILITIES.  GIVEN THE CONTINUED ESEWD MOVEMENT OF THE
   COLD FRONT...A 10-30 MILE WIDE ZONE HAS BEEN TRIMMED FROM THE WRN
   EXTENT OF THE SLIGHT.  MEANWHILE...STRONGER INSTABILITY AND
   INCREASING DEEP LAYER SHEAR ACROSS NERN TX WARRANTS THE INCLUSION OF
   THIS AREA TO THE SLIGHT RISK.
   
   OTHERWISE...THE FORECAST REMAINS CONSISTENT WITH EARLIER OUTLOOK
   ISSUANCES GIVEN OBJECTIVE ANALYSES SHOWING THE AIR MASS IN ADVANCE
   OF THE COLD FRONT HAS BECOME MODERATELY UNSTABLE /MLCAPE 1500-2500 J
   PER KG/.  IN ADDITION TO THE DESTABILIZATION...AN INCREASE IN
   MIDLEVEL WINDS ATTENDANT TO THE APPROACH OF A SHORTWAVE TROUGH...NOW
   ENTERING NWRN OK...WILL SUPPORT A FURTHER INCREASE IN DEEP LAYER
   SHEAR.  FORCING FOR ASCENT WITH THIS MIDLEVEL FEATURE SHOULD PROVE
   SUFFICIENT...GIVEN THE STRONG INSTABILITY...FOR ADDITIONAL TSTM
   DEVELOPMENT ALONG AND AHEAD OF THE COLD FRONT.  SHORT TERM MESOSCALE
   DETAILS FOR ERN OK/WRN AR INTO SWRN MO ARE AVAILABLE IN A RECENTLY
   ISSUED SPC MESOSCALE DISCUSSION /#2188/.  THE 30 PERCENT WIND/HAIL
   PROBABILITIES HAVE BEEN ADJUSTED TO INDICATE THE GREATEST
   CONCENTRATION OF SEVERE WEATHER LATER THIS AFTERNOON/EVENING.  
   
   THE 2 PERCENT TORNADO PROBABILITY HAS BEEN EXTENDED NEWD INTO NERN
   OK/NWRN AR AND SWRN MO GIVEN THAT A TORNADO CANNOT BE RULED OUT FROM
   NERN TX TO SWRN MO WHERE LOW LEVEL SHEAR IS ENHANCED SOME DUE TO
   BACKED SURFACE WINDS.  HOWEVER...THE LACK OF A FOCUSED SURFACE LOW
   OVER ERN OK SUPPORTING A MORE PERSISTENT BACKING OF LOW LEVEL WINDS
   ISALLOBARICALLY AND POSITIVE ORIENTATION OF MID/UPPER LEVEL TROUGH
   SHOULD PRECLUDE A GREATER TORNADO THREAT.
   
   ..PETERS.. 09/18/2011
   
   .PREV DISCUSSION... /ISSUED 1130 AM CDT SUN SEP 18 2011/
   
   ...SYNOPSIS...
   BROAD MULTI-STREAM TROUGH OVER THE PLNS STATES WILL CONTINUE E INTO
   THE MS VLY EARLY MON AS HEIGHTS RISE OVER THE RCKYS/GRT BASIN.  TWO
   IDENTIFIABLE VORT LOBES IN THE SRN PART OF THE TROUGH...ONE NOW OVER
   NW OK/S CNTRL KS AND THE OTHER NOW NEAR FWD...LIKELY WILL AFFECT
   TSTM DEVELOPMENT LATER TODAY OVER PARTS OF THE S CNTRL U.S.
   
   AT THE SFC...PATTERN WILL BE DOMINATED BY SLOWLY PROGRESSIVE COLD
   FRONT THAT ATTM EXTENDS FROM E CNTRL KS SSW INTO W CNTRL TX. 
   CONVERGENCE ALONG THE FRONT WILL...HOWEVER...BE COMPROMISED BY THE
   CONTINUING PRESENCE OF SEVERAL WEAK...SIMILARLY-ORIENTED WIND SHIFT
   LINES...CONFLUENCE ZONES...AND CONVECTIVE OUTFLOW BOUNDARIES AHEAD
   OF THE FRONT AS FAR E AS THE ARKLATEX.
   
   ...CNTRL TX TO WRN OZARKS THIS AFTN/EVE...
   SCTD BANDS/SMALL CLUSTERS OF STORMS EXPECTED TO PERSIST IN LOW LVL
   WAA ZONE WELL AHEAD OF COLD FRONT FROM CNTRL MO SSW TO THE ARKLATEX
   TODAY.  THE STORMS SHOULD MOVE/DEVELOP ENE INTO THE MID/LWR MS VLY
   THROUGH THE AFTN AND SHOULD REMAIN LARGELY SUB-SVR /GIVEN
   COMPARATIVELY WEAK INSTABILITY AND SHEAR/...DESPITE SOME LARGE SCALE
   FORCING FOR ASCENT OVER SRN SECTIONS PROVIDED BY THE N TX UPR
   IMPULSE.
   
   FARTHER W...BOUNDARY LAYER WILL REMAIN FAVORABLY MOIST AHEAD OF COLD
   FRONT...WITH PW AROUND 1.50 INCHES AND DEW POINTS IN THE LOW-MID 60S
   F FROM CNTRL TX NE INTO SE KS/FAR SW MO...WHERE MODERATE TO STRONG
   HEATING WILL OCCUR.  COUPLED WITH 500 MB TEMPS OF MINUS 9 TO MINUS
   11 C IN CORE OF UPR TROUGH...EXPECT SBCAPE TO RANGE FROM 1500 TO
   2500 J/KG BY MID AFTN FROM SW MO TO CNTRL TX.
   
   FORCING FOR ASCENT WILL INCREASE THIS AFTN ALONG AN ARC EXTENDING
   FROM SE KS/SW MO THROUGH ERN OK INTO N CNTRL TX AS OK/KS VORT LOBE
   CONTINUES ESEWD.  COUPLED WITH SFC HEATING...THIS SHOULD SUPPORT A
   BAND OF FAIRLY VIGOROUS STORM DEVELOPMENT FROM SW MO THROUGH ERN OK
   INTO CNTRL AND NE TX BY MID TO LATE AFTN.
   
   GIVEN DEGREE OF INSTABILITY AND RICH LOW LVL MOISTURE...RELATIVELY
   MODEST WIND FIELD /20-25 KT SW FLOW AT 850 MB VEERING TO 30 KT WLY
   WINDS AT 500 MB/ SHOULD BE SUFFICIENT FOR SUSTAINED MULTICELL
   CLUSTERS AND MARGINAL SUPERCELLS...WITH LARGE HAIL AND LOCALLY DMGG
   WINDS THE MAIN SVR THREAT.  SOME OF THE STORMS COULD MERGE INTO ONE
   OR TWO LARGER BANDS WITH EMBEDDED BOWING SEGMENTS...ESPECIALLY IN
   ERN OK/NERN TX.
   
   THE OK STORMS SHOULD MOVE E INTO THE OZARKS AND ARKLATEX THIS
   EVE...WHERE COMPARATIVELY WEAKER THERMODYNAMICS WILL EXIST. FARTHER
   SW...THE ACTIVITY OVER CNTRL/N TX...MEANWHILE...SHOULD ULTIMATELY BE
   UNDERCUT BY THE COLD FRONT.  TOGETHER WITH THE LOSS OF SFC
   HEATING...THIS SHOULD RESULT IN AN OVERALL WEAKENING OF THE SVR
   THREAT BY MID TO LATE EVE.
   
   CLICK TO GET WUUS01 PTSDY1 PRODUCT

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