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 181943
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0243 PM CDT THU AUG 18 2011
   
   VALID 182000Z - 191200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE NRN
   PLAINS...UPPER MS VALLEY AND MID-MO VALLEY...
   
   SEVERAL CHANGES HAVE BEEN MADE TO THE OUTLOOK AT 20Z. THE FIRST IS
   TO WIDEN THE SLIGHT RISK AREA MORE ACROSS ERN NEB...WRN IA AND
   NCNTRL MO WHERE AN MCS IS EXPECTED TO TRACK SSEWD LATE THIS
   AFTERNOON AND EARLY THIS EVENING. THE CLUSTER OF STORMS CURRENTLY
   APPROACHING THE OMAHA AREA IS LOCATED ALONG A SHARP NNW TO SSE
   GRADIENT OF STRONG INSTABILITY WITH VERY STEEP MID-LEVEL LAPSE
   RATES. IN ADDITION...WSR-88D VWPS SUGGEST DEEP LAYER SHEAR IS QUITE
   FAVORABLE FOR SUPERCELLS WITH LARGE HAIL. HAVE EXPANDED THE SIG HAIL
   THREAT AREA SEWD ACROSS MUCH OF ERN NEB AND FAR WRN IA. ALSO...HAVE
   EXPANDED THE 5 PERCENT TORNADO PROBABILITY SEWD INTO THE OMAHA AREA
   AS WELL. THE SECOND CHANGE IS TO ADD A 5 PERCENT WIND DAMAGE
   PROBABILITY IN WRN SC...WRN NC AND WCNTRL VA WHERE THUNDERSTORMS ARE
   DEVELOPING ON THE SERN FLANK OF THE HIGHER TERRAIN IN THE SRN
   APPALACHIAN MTNS. THE THIRD CHANGE IS TO EXPAND THE 5 PERCENT WIND
   DAMAGE PROBABILITY EWD FROM THE ST LOUIS AREA INTO SRN IL AND WRN KY
   WHERE THUNDERSTORMS ARE DEVELOPING ALONG AN AXIS OF STRONG
   INSTABILITY. THE FOURTH CHANGE IS TO REMOVE THE 5 PERCENT WIND
   DAMAGE PROBABILITY ACROSS SRN AND CNTRL AR...NE LA AND NW MS BEHIND
   THE SEVERE STORMS THAT ARE MOVING SWD THROUGH CNTRL MS.
   OTHERWISE...THE ONLY OTHER CHANGES ARE TO MAKE ADJUSTMENTS TO
   THUNDER-LINES.
   
   ..BROYLES.. 08/18/2011
   
   .PREV DISCUSSION... /ISSUED 1129 AM CDT THU AUG 18 2011/
   
   MORNING WATER VAPOR LOOPS SHOW A BROAD UPPER TROUGH DIGGING
   SOUTHEASTWARD ACROSS THE CANADIAN ROCKIES INTO MT.  MID LEVEL WINDS
   ARE FORECAST TO STRENGTHEN LATER TODAY IN ADVANCE OF THE APPROACHING
   SYSTEM...WITH SEVERAL WEAK SHORTWAVE TROUGHS EXPECTED TO MOVE ACROSS
   THE NORTHERN PLAINS.  THIS WILL RESULT IN A THREAT FOR LOCALLY
   SEVERE WEATHER ALONG TWO AXES...ONE FROM CENTRAL MN INTO SD...AND
   THE OTHER FROM SD SOUTHEASTWARD ALONG THE MO RIVER INTO NORTHEAST
   KS.
   
   ...MN INTO SD...
   STRONG HEATING IS OCCURRING TODAY OVER MUCH OF MN/SD. 
   MEANWHILE...SOUTHWESTERLY LOW LEVEL WINDS ARE EXPECTED TO STRENGTHEN
   SOMEWHAT THROUGH THE AFTERNOON WHICH WILL HELP TO DRAW UPPER 60S
   DEWPOINTS THAT LIE FARTHER SOUTH INTO THE REGION.  A CORRIDOR OF
   STRONG INSTABILITY WILL LIKELY DEVELOP FROM CENTRAL MN INTO CENTRAL
   SD WITH A RATHER WEAK CAP.  SCATTERED THUNDERSTORMS ARE FORECAST BY
   MOST MODEL SOLUTIONS TO DEVELOP ALONG THIS CORRIDOR.  EFFECTIVE
   VERTICAL SHEAR PROFILES AND STRONG CAPE SUGGEST THE RISK OF
   SUPERCELLS CAPABLE OF VERY LARGE HAIL AND DAMAGING WINDS.  AN
   ISOLATED TORNADO CANNOT BE RULED OUT.  STORMS WILL SAG SOUTHWARD
   THROUGH THE EVENING INTO SOUTHWEST MN AND EASTERN SD WITH A
   CONTINUED SEVERE THREAT.
   
   ...ERN SD/WRN IA/ERN NEB/WRN MO/ERN KS...
   A WEAKENING LOW LEVEL BAROCLINIC ZONE IS PRESENT THIS MORNING FROM
   CENTRAL SD SOUTHEASTWARD ROUGHLY ALONG THE MO RIVER INTO MO.  THE
   INSTABILITY GRADIENT IN THIS REGION IS BECOMING MORE DIFFUSE AS
   SURFACE DEWPOINTS MIX EASTWARD INTO IA/MN.  NEVERTHELESS...THIS
   GENERAL CORRIDOR IS EXPECTED TO BE THE FOCUS FOR MULTIPLE ROUNDS OF
   STRONG/SEVERE STORMS THIS AFTERNOON AND TONIGHT.  MULTIPLE MODELS
   INDICATE STORMS MAY DEVELOP BY MID AFTERNOON OVER SOUTHEAST SD AND
   TRACK ALONG THIS AXIS INTO IA.  OUTFLOW BOUNDARIES FROM INITIAL
   STORMS MAY PROVIDE A FOCUS FOR RENEWED CONVECTION THROUGH THE
   EVENING.  STRONG CAPE VALUES AND STRONG VERTICAL SHEAR WILL PROMOTE
   SUPERCELL STRUCTURES CAPABLE OF LARGE HAIL AND DAMAGING WINDS.  THE
   STRONG INSTABILITY EXTENDS WESTWARD ACROSS MUCH OF NEB...BUT A
   FORMIDABLE CAPPING INVERSION IS EXPECTED TO SUPPRESS ROBUST
   CONVECTION ACROSS CENTRAL/WESTERN NEB.
   
   ...MS/LA...
   A PERSISTENT CLUSTER OF THUNDERSTORMS OVER NORTHERN MS IS LIKELY TO
   TRACK SOUTHWARD ALL THE WAY TO THE GULF COAST.  RATHER STRONG
   HEATING AND DEWPOINTS IN THE MID 70S WILL HELP TO MAINTAIN STORM
   INTENSITY.  VERTICAL SHEAR IS WEAK AND STORM MOTION IS RATHER SLOW.
   HOWEVER...MESOSCALE ORGANIZATION OF COLD POOL MAY HELP TO PRODUCE
   LOCALLY GUSTY/DAMAGING WINDS ALONG THE MCS LEADING EDGE THIS
   AFTERNOON.
   
   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z