May 21, 2011 1300 UTC Day 1 Convective Outlook
Updated: Sat May 21 12:59:04 UTC 2011
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20110521 1300 UTC Day 1 Outlook Graphic
Probabilistic Tornado Graphic
20110521 1300 UTC Day 1 Tornado Probabilities 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
20110521 1300 UTC Day 1 Damaging Wind Probabilities 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
20110521 1300 UTC Day 1 Large Hail Probabilities 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 211255
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0755 AM CDT SAT MAY 21 2011
   
   VALID 211300Z - 221200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS FROM ERN PORTIONS OF THE
   SRN/CNTRL PLNS INTO MID MS/LWR OH VLYS...
   
   ...SYNOPSIS...
   SW SD CLOSED LOW SHOULD DRIFT SLOWLY ENE TODAY/TONIGHT...REACHING NE
   SD BY 12Z SUN AS SEVERAL SHORTWAVE IMPULSES MOVE E/NE ALONG ITS SRN
   AND ERN SIDES.  AT THE SFC...SEVERAL WEAK FRONTS/TROUGHS WILL
   PINWHEEL AROUND A SFC LOW OVER SD THAT SHOULD TRACK SLOWLY E IN
   TANDEM WITH UPR LOW.  THE MOST IMPORTANT BOUNDARY FOR TSTM
   DEVELOPMENT LIKELY WILL BE PACIFIC FRONT/DRYLINE THAT SHOULD ADVANCE
   SLIGHTLY EWD ACROSS PARTS OF KS...OK...AND NE TX TODAY
   ...BEFORE RETREATING WWD ONCE AGAIN OVERNIGHT.  FARTHER NE...A
   DIFFUSE WARM FRONT WILL MOVE/REDEVELOP NE ACROSS THE UPR MS AND UPR
   GRT LKS LATER TODAY THROUGH EARLY SUN.
   
   ...SRN/CNTRL PLNS INTO THE LWR MO/MID MS/LWR OH VLYS...
   LOW LVL ASCENT/RICH MOISTURE INFLOW ATOP OUTFLOW BOUNDARY/COLD POOL
   LEFT BY OVERNIGHT MCS THAT WEAKENED OVER E TX AND THE LWR MS
   VLY...IN CONJUNCTION WITH CONTINUED EWD ADVECTION OF MID LVL
   EML...MAY FOSTER ADDITIONAL STORM DEVELOPMENT OVER E TX AND LA
   THROUGH LATE THIS MORNING.  AMPLE ELEVATED CAPE WILL BE PRESENT FOR
   HAIL AND POSSIBLY LOCALLY DMGG WIND IN THE STRONGEST STORMS.
   GIVEN RICH MOISTURE INFLOW /PW AOA 1.75 INCHES WITH SFC DEWPOINTS IN
   THE 70S F/ AND MODERATE SFC HEATING...SOME CHANCE WILL EXIST FOR
   THESE STORMS WILL PERSIST AND BECOME SFC-BASED THIS AFTN.  WERE THIS
   TO OCCUR...POTENTIAL WOULD EXIST FOR VERY LARGE HAIL...DMGG
   WINDS...AND POSSIBLY A TORNADO OR TWO AS THE ACTIVITY MERGES INTO
   ONE OR TWO SMALL CLUSTERS.  THESE COULD BUILD SWWD ALONG MOISTURE
   GRADIENT/SFC TROUGH INTO CNTRL TX BY LATER IN THE DAY.
   
   N OF THIS ACTIVITY...SOMEWHAT WEAKER MOIST BOUNDARY LAYER FLOW WILL
   SPREAD MID TO UPR 60S F DEWPOINTS NWD INTO ERN THIRD OF OK...AND
   NEWD INTO SE MO AND THE LWR OH/LWR TN VLYS.  COMBINATION OF ASCENT
   DOWNSTREAM FROM AN UPR IMPULSE ROTATING NEWD FROM WRN KS WITH STEEP
   MID LVL LAPSE RATES /500 MB TEMPS AROUND -16C/ AND STRONG SFC
   HEATING SHOULD FOSTER SCTD TSTM DEVELOPMENT IN AN ARC ALONG SFC
   FRONT/TROUGH FROM CNTRL/ERN NEB SWD INTO ERN KS AND ERN OK BY MID TO
   LATE AFTN.  SOME OF THE STORMS...ESPECIALLY IN OK AND KS...WILL BE
   SUPERCELLS.  WITH SBCAPE RANGING FROM AROUND 2000 J/KG IN NEB TO
   GREATER THAN 3000 J/KG IN OK...THREAT WILL EXIST FOR VERY LARGE HAIL
   AND DMGG WIND.  TORNADOES WILL ALSO BE POSSIBLE...ESPECIALLY TOWARD
   EVE OVER ERN OK AND KS AS LLJ STRENGTHENS.  SOME OF THE STORMS COULD
   EVOLVE INTO ONE OR TWO MCSS THAT SPREAD A THREAT ISOLD DMGG WIND AND
   HAIL E OR ENE INTO THE MID MS/LWR OH VLYS OVERNIGHT.
   
   FARTHER E AND NE...A SEPARATE AREA OF STORMS MAY FORM THIS AFTN IN
   ZONE OF FAIRLY STRONG LOW LVL MOISTURE INFLOW AND SFC HEATING FROM
   ERN AR AND PERHAPS ERN MO E/NE INTO PARTS OF IL/IND AND PERHAPS WRN
   KY/TN.  SOME OF THIS ACTIVITY MAY BE AUGMENTED BY SRN PART OF
   AFOREMENTIONED IMPULSE ROTATING NEWD FROM THE SRN PLNS... AND COULD
   CONTAIN BOWING SEGMENTS WITH A RISK FOR DMGG WIND.
   
   ..CORFIDI/SMITH.. 05/21/2011
   
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   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z