Categorical Graphic
Probabilistic Tornado Graphic
Probabilistic Damaging Wind Graphic
Probabilistic Large Hail Graphic

   SPC AC 272000
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0200 PM CST SUN FEB 27 2011
   
   VALID 272000Z - 281200Z
   
   ...THERE IS A MDT RISK OF SVR TSTMS ACROSS MUCH OF AR/SOUTHERN MO
   AND TO SOUTHERN IL/SOUTHWEST INDIANA TO WESTERN PORTIONS OF TN/KY...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS FROM SOUTHERN KS AND
   NORTHERN/EASTERN OK AND NORTHEAST TX NEWD TO THE OH/TN VALLEYS...
   
   ...MID-SOUTH/OZARKS/MIDDLE MS VALLEY/LOWER OH VALLEY...
   SURFACE BASED INHIBITION CONTINUES TO WEAKEN THIS AFTERNOON IN THE
   PRESENCE OF RETREATING MOISTURE AS CURRENTLY GENERALIZED BY LOWER
   60S F SURFACE DEWPOINTS. GIVEN THIS WEAKENING INHIBITION...AT THE
   VERY LEAST...A CONDITIONAL SURFACE BASED SUPERCELL/TORNADO THREAT
   WILL EXIST AMID THE RETREATING BOUNDARY/ZONE OF DIFFERENTIAL HEATING
   IN PROXIMITY TO A STRENGTHENING LOW LEVEL JET AXIS. PERHAPS
   CORRELATED TO A BAND OF MID LEVEL ASCENT IMPLIED NEAR THE ARKLATEX
   AT MID AFTERNOON PER SATELLITE IMAGERY...12Z BASED GUIDANCE SUCH AS
   THE NAM/WRF-NMM AS WELL AS VARIOUS HRRR RUNS REFLECT SUCH POTENTIAL
   WITHIN THIS CORRIDOR. A MORE WIDESPREAD/SUBSTANTIAL SEVERE
   THREAT...INCLUDING THE POSSIBILITY OF STRONG TORNADOES AND DAMAGING
   WINDS...IS STILL EXPECTED TO OTHERWISE EVOLVE LATER TONIGHT.
   
   ...SOUTHERN PLAINS/LOWER MO VALLEY/OZARKS...
   ELEVATED TSTMS CAPABLE OF SEVERE HAIL WILL CONTINUE TO INCREASE THIS
   AFTERNOON ON THE COOL SIDE OF THE SOUTHWEST-NORTHEAST ORIENTED
   SURFACE FRONTAL ZONE. ADDITIONAL SURFACE BASED TSTM WILL BE POSSIBLE
   BY AROUND LATE AFTERNOON ACROSS OK/SOUTHEAST KS INTO SOUTHERN
   MO/NORTHERN AR...SEE PRIOR DISCUSSION BELOW AND SUBSEQUENT MESOSCALE
   DISCUSSIONS/POSSIBLE WATCHES.
   
   ..GUYER.. 02/27/2011
   
   .PREV DISCUSSION... /ISSUED 1030 AM CST SUN FEB 27 2011/
   
   ...MID SOUTH/LOWER OH VALLEY THIS AFTERNOON THROUGH TONIGHT...
   THE AXIS OF RICHEST LOW-LEVEL MOISTURE EXTENDS NEWD FROM SE TX TO NW
   MS AND ERN AR...ALONG THE LLJ AXIS.  CONTINUED NWD/NEWD EXPANSION OF
   THE WARM SECTOR AND SOME SURFACE HEATING IN CLOUD BREAKS WILL RESULT
   IN SUFFICIENT DESTABILIZATION /MLCAPE OF 1000-1500 J PER KG/ FOR
   SEVERE STORMS IN THE WARM SECTOR BY MID-LATE AFTERNOON.  VERTICAL
   SHEAR PROFILES WILL BE FAVORABLE FOR SUPERCELLS WITH EFFECTIVE BULK
   SHEAR IN EXCESS OF 50 KT AND EFFECTIVE SRH AOA 300 M2/S2.  
   
   THE PRIMARY CONCERNS THIS AREA DURING THE AFTERNOON WILL BE A FOCUS
   FOR STORM INITIATION...THE INFLUENCE OF CLOUDS ON SURFACE
   HEATING...AND EWD EXPANSION OF THE ELEVATED MIXED LAYER/CAP. 
   ASSUMING A FEW STORMS CAN FORM THIS AFTERNOON FROM NE AR INTO WRN
   TN...THE ENVIRONMENT WILL BE FAVORABLE FOR TORNADIC SUPERCELLS...AND
   THE POTENTIAL FOR A STRONG TORNADO OR TWO.  OTHERWISE...AN INCREASE
   IN THUNDERSTORMS IS EXPECTED OVERNIGHT IN ADVANCE OF THE EJECTING
   MIDLEVEL TROUGH AND ALONG THE LLJ CORRIDOR...ALONG/IN ADVANCE OF THE
   COLD FRONT MOVING EWD FROM OK ACROSS AR.  THE PRE-FRONTAL CONVECTION
   MAY CONTAIN SUPERCELLS WITH A CONTINUED TORNADO RISK OVERNIGHT INTO
   THE LOWER OH VALLEY...WHILE A MORE LINEAR CONVECTIVE MODE IS
   EXPECTED TO EVOLVE ALONG THE COLD FRONT BY 09-12Z.  DAMAGING WINDS
   WILL BE THE MAIN THREAT WITH THE FRONTAL CONVECTIVE BAND...THOUGH
   QLCS TORNADOES WILL ALSO BE POSSIBLE.
   
   ...KS/OK BORDER THIS EVENING INTO NRN MO/IL OVERNIGHT...
   THE INITIAL LEE CYCLONE IN SE CO WILL DEVELOP EWD ALONG THE KS/OK
   BORDER THIS EVENING INTO EARLY TONIGHT IN RESPONSE TO THE MIDLEVEL
   SHORTWAVE TROUGH THAT WILL EJECT ENEWD OVER THE SRN HIGH PLAINS. 
   SLY FLOW INDUCED BY THE LEE CYCLONE HAS RESULTED IN AN INCREASE IN
   LOW-LEVEL MOISTURE IN THE WARM SECTOR INTO OK...WITH BOUNDARY LAYER
   DEWPOINTS EXPECTED TO HOLD IN THE LOW 60S THROUGH THE AFTERNOON. 
   SURFACE HEATING WILL BE INHIBITED BY LOW STRATUS AND A SEPARATE BELT
   OF MID-HIGH CLOUDS NOW OVERSPREADING THE ERN TX PANHANDLE/NW TX AND
   WRN OK.  HOWEVER...CLEARING FROM THE W IS EXPECTED OVER THE DRYLINE
   AND TRIPLE POINT BY ABOUT 21Z...AND THIS SURFACE HEATING WILL
   CORRESPOND WITH INCREASING LOW-LEVEL ASCENT AND LOCAL WEAKENING OF
   CONVECTIVE INHIBITION.  THUS...AT LEAST ISOLATED THUNDERSTORM
   DEVELOPMENT IS EXPECTED IN THE 22-00Z TIME FRAME NEAR THE TRIPLE
   POINT INVOF THE KS/OK BORDER...W OF I-35.  
   
   A COMBINATION OF 7-8 C/KM MIDLEVEL LAPSE RATES ABOVE BOUNDARY LAYER
   DEWPOINTS OF 58-62 F...AND AFTERNOON SURFACE TEMPERATURES IN THE LOW
   70S...WILL SUPPORT MLCAPE NEAR 1500 J/KG.  EFFECTIVE BULK SHEAR OF
   50-70 KT WILL FAVOR SUPERCELLS CAPABLE OF PRODUCING LARGE HAIL...AND
   A COUPLE OF TORNADOES WILL BE POSSIBLE BEFORE STORMS CROSS INTO THE
   COOL AIR N OF THE WARM FRONT.  OTHERWISE... ELEVATED THUNDERSTORMS
   WILL EXPAND NEWD ACROSS SRN AND ERN KS INTO MO AND IL OVERNIGHT IN
   ADVANCE OF THE SURFACE LOW...WITH A CONTINUED RISK FOR LARGE HAIL.
   
   CLICK TO GET WUUS01 PTSDY1 PRODUCT

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