Aug 18, 2009 1300 UTC Day 1 Convective Outlook
Updated: Tue Aug 18 12:40:18 UTC 2009
Probabilistic to Categorical Outlook Conversion Table (Effective Feb 14, 2006).
Categorical Graphic
20090818 1300 UTC Day 1 Outlook Graphic
Probabilistic Tornado Graphic
20090818 1300 UTC Day 1 Tornado Probabilities Graphic
Torndao Legend Image
Probabilistic Damaging Wind Graphic
20090818 1300 UTC Day 1 Damaging Wind Probabilities Graphic
Wind Legend Image
Probabilistic Large Hail Graphic
20090818 1300 UTC Day 1 Large Hail Probabilities Graphic
Hail Legend Image
   SPC AC 181236
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0736 AM CDT TUE AUG 18 2009
   
   VALID 181300Z - 191200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS PARTS OF THE SRN/CENTRAL HIGH
   PLAINS...
   
   ...SRN/CENTRAL HIGH PLAINS...
   WITH LITTLE CHANGE IN THE OVERALL SYNOPTIC PATTERN ACROSS THIS
   REGION...SEVERE THREAT AREAS WILL BE MITIGATED BY PRECEEDING
   THUNDERSTORMS AND LOCATION OF RESIDUAL OUTFLOW BOUNDARIES LATER
   TODAY.  MODELS FAIL TO PROPERLY HANDLE EARLY MORNING MCS OVER OK AND
   ITS EXPECTED SUPPRESSION OF MOIST/UNSTABLE AIR MASS SWD INTO WRN
   TX/SERN OK THIS MORNING.  THIS GIVES LITTLE CREDENCE TO MODEL
   FORECAST OF MODERATE TO STRONG INSTABILITY FROM CENTRAL/NWRN OK INTO
   NERN NM/SERN CO LATER TODAY...AND WOULD NOT BE SURPRISED TO SEE THIS
   AXIS DEVELOP FARTHER SSW THAN CURRENTLY PROGGED. EXPECT LEADING LINE
   AHEAD OF ONGOING MCS WILL CONTINUE SHIFTING ESEWD INTO SRN/ERN OK
   THIS MORNING...ALTHOUGH SHEAR WEAKENS WITH SEWD EXTENT AND MAY TEND
   TO WEAKEN OVERALL ORGANIZATION OF THIS ACTIVITY.  AN ISOLATED
   STRONG/SEVERE STORM COULD ACCOMPANY THE MORNING MCS...BUT OVERALL
   SEVERE THREAT SHOULD BE LIMITED FOR MUCH OF THE DAY.
   
   GREATER THREAT SHOULD EVOLVE NEAR THE HIGHER TERRAIN OF NRN
   NM/SRN-CENTRAL CO DURING THE MID TO LATE AFTERNOON AS PRONOUNCED
   SHORTWAVE TROUGH NOW OVER ERN UT/WRN CO SHIFTS EWD ACROSS CO. DEEP
   ASCENT AHEAD OF THIS WELL DEFINED VORT MAX MAY SUPPORT EARLIER
   DEVELOPMENT OVER THE HIGH PLAINS AS COMPARED TO THE PAST FEW DAYS. 
   AIRMASS JUST EAST OF THE HIGH TERRAIN WILL BE QUITE MOIST AND SHOULD
   DESTABILIZE SUFFICIENTLY FOR SEVERAL CLUSTERS OF SEVERE STORMS
   SPREADING ESEWD THROUGH THE EVENING. AS WAS THE CASE MONDAY...SHEAR
   WILL BE MORE THAN SUFFICIENT FOR SUPERCELLS WITH THREATS OF LARGE
   HAIL...INCLUDING ISOLATED SIGNIFICANT HAIL...AND ISOLATED DAMAGING
   WINDS WITHIN VERY STEEP LAPSE RATES OVER THE HIGH PLAINS. 
   INCREASING SLY LLJ LATE TODAY/THIS EVENING AHEAD OF MID LEVEL
   SHORTWAVE TROUGH SHOULD ALSO SUPPORT AN ISOLATED TORNADO THREAT AS
   LOW LEVEL SHEAR STRENGTHENS OVER THE HIGH PLAINS.  
   
   ADDITION DEVELOPMENT MAY OCCUR LATE TODAY INVOF SURFACE OUTFLOW
   BOUNDARY AS CAP WEAKENS.  ALTHOUGH CONFIDENCE IN PLACING THIS
   BOUNDARY REMAINS LOW ATTM...WRN PORTION MAY ERODE/LIFT NWD INTO THE
   TX PANHANDLE/WRN OK BY LATE IN THE DAY.  INCREASING SLY LLJ ACROSS
   THE SRN HIGH PLAINS OVERNIGHT SHOULD ONCE AGAIN SUPPORT MCS ACTIVITY
   TRACKING ESEWD TONIGHT WITH SEVERE THREAT GRADUALLY DIMINISHING
   DURING THE MID TO LATE EVENING.
   
   ...WRN NEB INTO THE CENTRAL/ERN DAKOTAS...
   NRN STREAM TROUGH ALOFT WILL REMAIN POSITIVELY-TILTED ACROSS THIS
   REGION TODAY WITH A SERIES OF COMPACT SHORTWAVE TROUGHS DIGGING
   SEWD. THIS WILL SUSTAIN ASCENT ATOP DEVELOPING MARGINAL INSTABILITY
   THIS AFTERNOON ACROSS THIS REGION...WITH MODELS CONSISTENT IN
   DEVELOPING DIURNAL THUNDERSTORMS INVOF SSW-NNE ORIENTED SURFACE
   TROUGH FROM THE CENTRAL HIGH PLAINS TOWARDS SERN ND.  SHEAR REMAINS
   FAIRLY STRONG AND SHOULD SUPPORT A FEW ORGANIZED STORMS...ALTHOUGH
   SEVERITY MAY BE TEMPERED BY RELATIVELY DRY BOUNDARY LAYER AND
   RESULTANT WEAK TO MARGINAL INSTABILITY INTO THE DAKOTAS.
   
   ...OZARK REGION INTO THE OH VALLEY AND LOWER GREAT LAKES...
   AXIS OF LOW LEVEL MOISTURE IS ALREADY IN PLACE WITH DEEP MOISTURE
   PLUME EVIDENT ON GOES-PW DATA/MORNING SOUNDINGS FROM ERN OK/SERN KS
   THROUGH THE OH VALLEY INTO THE LOWER GREAT LAKES REGION. ALTHOUGH
   LAPSE RATES WILL REMAIN QUITE WEAK WITHIN THIS MOISTURE
   PLUME...SUFFICIENT HEATING AND ASCENT AHEAD OF SURFACE FRONT SHOULD
   SUPPORT SCATTERED THUNDERSTORMS AND MODEST INSTABILITY THIS
   AFTERNOON OVER THIS LARGE REGION. EFFECTIVE BULK SHEAR OF 25-30 KT
   SUGGESTS POTENTIAL FOR MULTICELLS WITH LOCALLY STRONG WIND GUSTS
   BEING THE PRIMARY THREAT WITH THE MORE ORGANIZED STORMS TODAY.
   
   ..EVANS/JEWELL.. 08/18/2009
   
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   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z