Feb 27, 2011 1300 UTC Day 1 Convective Outlook
Updated: Sun Feb 27 12:55:43 UTC 2011
Probabilistic to Categorical Outlook Conversion Table
Public Severe Weather Outlook

The SPC is forecasting ...significant severe thunderstorms expected over parts of the ozark plateau into mid-south/lower ohio valley later today and tonight....   Please read the latest public statement about this event.

Categorical Graphic
20110227 1300 UTC Day 1 Outlook Graphic
Probabilistic Tornado Graphic
20110227 1300 UTC Day 1 Tornado Probabilities Graphic
Torndao Legend Image
Probabilistic Damaging Wind Graphic
20110227 1300 UTC Day 1 Damaging Wind Probabilities Graphic
Wind Legend Image
Probabilistic Large Hail Graphic
20110227 1300 UTC Day 1 Large Hail Probabilities Graphic
Hail Legend Image
   SPC AC 271253
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0653 AM CST SUN FEB 27 2011
   
   VALID 271300Z - 281200Z
   
   ...THERE IS A MDT RISK OF SVR TSTMS OVER PORTIONS OF AR...SERN
   MO...WRN PARTS OF TN AND KY...SRN IL AND FAR SWRN IND...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS FROM PARTS OF THE CNTRL/SRN
   PLAINS NEWD THROUGH MUCH OF THE OH VALLEY...
   
   ...SYNOPSIS...
   
   MID AND UPPER-LEVEL CYCLONE OVER THE LOWER CO VALLEY WILL BECOME
   INCREASINGLY SHEARED WHILE TRANSLATING EWD INTO CONFLUENT FLOW
   REGIME IN PLACE E OF THE ROCKIES.  THE LEADING PORTION OF THIS
   SYSTEM IS FORECAST TO REACH THE CNTRL/SRN HIGH PLAINS BY AFTERNOON
   PRIOR TO LOSING AMPLITUDE WHILE EJECTING NEWD INTO THE UPPER MIDWEST
   OVERNIGHT.  IN ITS WAKE...THE MORE SUBSTANTIAL...REMAINING PORTION
   OF MIDLEVEL TROUGH WILL SHIFT EWD THROUGH THE CNTRL/SRN PLAINS
   TOWARD THE MID/LOWER MS VALLEYS BY 28/12Z.
   
   AT THE SURFACE...LEE CYCLONE NOW DEEPENING OVER ERN CO IS FORECAST
   TO DEVELOP TO THE VICINITY OF THE OK/KS BORDER NEAR OR JUST W OF
   I-35 BY 28/00Z BEFORE ACCELERATING NEWD THROUGH CNTRL MO AND THE OH
   VALLEY TONIGHT.  AN ASSOCIATED WARM FRONT WILL LIFT NWD THROUGH THE
   OZARKS AND MID MS/OH VALLEYS IN ADVANCE OF THIS INITIAL SURFACE LOW
   WHILE A TRAILING COLD FRONT PUSHES SEWD THROUGH THE SRN PLAINS. 
   ELSEWHERE...A DRYLINE WILL MIX EWD TO THE VICINITY OF I-35 IN OK/N
   TX BY LATE AFTERNOON BEFORE BEING OVERTAKEN BY PACIFIC FRONT WHICH
   WILL SURGE EWD TOWARD THE LOWER MS VALLEY IN TANDEM WITH PRIMARY
   PORTION OF UPPER TROUGH.  THERE IS SOME INDICATION THAT A SECONDARY
   SURFACE LOW MAY FORM TONIGHT AT THE INTERSECTION OF THE COLD AND
   PACIFIC FRONTS NEAR THE CONFLUENCE OF THE MS AND OH VALLEYS.
   
   ...CNTRL/SRN PLAINS INTO THE OH VALLEY AND MID-SOUTH...
   
   LATEST MESOSCALE AND CONVECTION-ALLOWING MODEL GUIDANCE HAS TRENDED
   TOWARD A HIGHER PROBABILITY OF DIURNAL TSTM DEVELOPMENT THIS
   AFTERNOON INTO EVENING FROM THE VICINITY OF SURFACE TRIPLE POINT
   OVER S-CNTRL KS/N-CNTRL OK NEWD TOWARD MKC.  HERE...DEEP ASCENT IN
   EXIT REGION OF UPPER JET STREAK /ATTENDANT TO LEAD IMPULSE MENTIONED
   ABOVE/ COUPLED WITH A STRENGTHENING FRONTOGENETICAL CIRCULATION ARE
   EXPECTED TO OVERCOME CAP...SUPPORTING TSTM DEVELOPMENT ALONG OR ON
   IMMEDIATE COOL SIDE OF SURFACE BOUNDARY.  STEEP MIDLEVEL LAPSE RATES
   AND BOUNDARY LAYER DEW POINTS IN THE UPPER 50S TO LOWER 60S WILL
   YIELD A MODERATELY UNSTABLE ENVIRONMENT WITH MLCAPE VALUES
   APPROACHING 1000 J/KG.  MOREOVER...LOCALLY BACKED NEAR-SURFACE WINDS
   BENEATH SWLY MIDLEVEL FLOW INCREASING TO 80-90 KT WILL RESULT IN
   MORE THAN SUFFICIENT VERTICAL SHEAR FOR ORGANIZED STORMS INCLUDING
   SUPERCELLS.  THE PRIMARY HAZARD APPEARS TO BE HAIL...THOUGH A
   TORNADO OR TWO IS POSSIBLE WITH ANY STORMS ROOTED IN THE BOUNDARY
   LAYER.
   
   EXPECT A RAPID DOWNSTREAM EXPANSION IN STRONG TO SEVERE TSTMS
   TONIGHT FROM THE MID MS VALLEY EWD THROUGH THE OH VALLEY ALONG AND S
   OF WARM FRONT AND IN ADVANCE OF MIGRATORY SURFACE LOW.  AMBIENT
   ENVIRONMENT WILL BE CHARACTERIZED BY MARGINAL INSTABILITY /I.E.
   MLCAPE VALUES GENERALLY LESS THAN 500 J PER KG/ BUT VERY STRONG LOW
   AND DEEP-LAYER SHEAR.  AS SUCH...THE POTENTIAL WILL EXIST FOR
   FAST-MOVING SUPERCELL AND/OR BOWING STORM CLUSTERS WITH A THREAT FOR
   DAMAGING WINDS AND TORNADOES.
   
   A SECOND...POTENTIALLY HIGHER IMPACT TSTM REGIME MAY DEVELOP LATE
   THIS AFTERNOON OR MID/LATE EVENING FROM PORTIONS OF CNTRL/NERN AR
   NEWD INTO THE LOWER OH VALLEY...ALONG RETREATING WARM FRONT OR
   PERHAPS IN THE WAKE OF THE FRONT ALONG A CONFLUENCE ZONE DEVELOPING
   WITHIN THE OPEN WARM SECTOR.  HERE...SEVERAL MESOSCALE AND
   CONVECTION-ALLOWING MODELS DEVELOP A DISTINCTLY SEPARATE AREA OF
   CONVECTIVE PRECIPITATION WHICH EVENTUALLY MERGES WITH
   ABOVE-MENTIONED CORRIDOR OF STORMS TRAVERSING THE OH VALLEY.  GIVEN
   THE MOIST/LOW LCL ENVIRONMENT...STRONG VERTICAL SHEAR AND POTENTIAL
   FOR A MORE DISCRETE STORM MODE...IT APPEARS THAT THIS SETUP WOULD
   FOSTER THE GREATEST THREAT FOR SIGNIFICANT TORNADOES IN ADDITION TO
   HAIL AND LOCALLY DAMAGING WIND GUSTS.
   
   A THIRD SVR TSTM EPISODE IS EXPECTED TO TAKE SHAPE ACROSS PARTS OF
   ERN OK/WRN AR THIS EVENING INTO TONIGHT AS A PACIFIC FRONT OVERTAKES
   THE DRYLINE AND SURGES EWD IN CONCERT WITH THE MAIN PORTION OF THE
   UPPER TROUGH.  INITIAL STORM MODE MAY BE SUPERCELLULAR...THOUGH A
   RAPID TRANSITION TO QLCS IS EXPECTED WITH THE CONVECTIVE SYSTEM
   REACHING WRN TN AND THE MS DELTA REGION BY THE END OF THE D1 PERIOD.
   HERE TOO...VERTICAL SHEAR WILL BE QUITE STRONG AND SUPPORTIVE OF
   EMBEDDED SUPERCELL AND/OR BOWING STRUCTURES CAPABLE OF POTENTIALLY
   WIDESPREAD DAMAGING WINDS AND A FEW TORNADOES.
   
   ..MEAD/HURLBUT.. 02/27/2011
   
   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z