Categorical Graphic
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Probabilistic Damaging Wind Graphic
Probabilistic Large Hail Graphic

   SPC AC 131959
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0259 PM CDT WED MAY 13 2009
   
   VALID 132000Z - 141200Z
   
   ...THERE IS A MDT RISK OF SVR TSTMS ACROSS CENTRAL AND SRN
   IL...MO...SERN KS...NWRN AR AND A LARGE PORTION OF OK...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MODERATE RISK
   FROM THE SRN PLAINS NEWD INTO THE GREAT LAKES...
   
   ...ERN IA/IL/NRN AND CENTRAL MO...
   AS COLD FRONT AND JET MAX MOVE INTO THE AREA THIS AFTERNOON...
   WIDESPREAD THUNDERSTORMS ARE LIKELY TO DEVELOP ALONG FRONT. WIND
   PROFILES REMAIN FAVORABLE FOR TORNADOES AND WIND DAMAGE...
   ESPECIALLY IA/IL SWWD INTO MO WHERE STRONGER ENVIRONMENTAL
   WINDS/DEEP LAYER SHEAR IS SPREADING INTO THE AREA FROM THE WEST.
   HOWEVER...EFFECTIVE WARM FRONT...GENERALLY NORTH OF A SLO NWWD INTO 
   SRN IA...HAS LIMITED HEATING AND GREATER DESTABILIZATION THAN
   EARLIER ANTICIPATED. WHILE A LINE OF STORMS IS STILL LIKELY TO
   DEVELOP ALONG THE FRONT BY LATE AFTERNOON...ALONG WITH A CHANCE OF
   EMBEDDED SUPERCELLS/TORNADOES...THE RELATIVELY COOL BOUNDARY LAYER
   SUGGESTS THAT THE GREATER POTENTIAL FOR MORE WIDESPREAD SEVERE
   WEATHER WILL BE ALONG AND SOUTH OF THE WARM FRONT. ALSO...AN MCV WAS
   LOCATED ABOUT 70 MILES SW OF STL...HEADING NEWD AT 35 KT. THIS
   SYSTEM WILL ENHANCE THE SEVERE WEATHER THREAT AHEAD OF IT AS IT
   MOVES NEAR THE STL AREA AROUND 21Z AND NEWD INTO SRN/CENTRAL IL
   THEREAFTER.
   
   ...SWRN MO/SERN KS/OK...
   ALTHOUGH 18Z SOUNDINGS AT OKC/TOP AND SGF SHOWED FAIRLY STOUT
   CAPPING INVERSIONS...STRONG CONVERGENCE ALONG SEWD MOVING COLD FRONT
   SHOULD SUPPLY PLENTY OF LIFT FOR NUMEROUS THUNDERSTORMS TO DEVELOP
   BETWEEN 21-00Z. ALTHOUGH DEEP LAYER SHEAR WILL NOT BE EXTREMELY
   STRONG...AROUND 30 KT...MLCAPES FROM 3500 TO 4000 J/KG WILL FAVOR
   SUPERCELL STRUCTURES. THE NEARLY DRY ADIABATIC MID LEVEL LAPSE RATES
   AND DEGREE OF INSTABILITY ARE LIKELY TO YIELD VERY LARGE HAIL WITH
   INITIAL STORMS. HOWEVER...THE STORMS SHOULD CONGEAL INTO A
   LINE/EMBEDDED BOWS...WITH WIND DAMAGE BECOMING THE GREATER THREAT
   TONIGHT...AS STORMS FORWARD PROPAGATE SEWD/SSEWD INTO A DEVELOPING
   LOW LEVEL JET AND AXIS OF GREATER INSTABILITY. ISOLATED SUPERCELLS
   MAY ALSO DEVELOP IN WESTERN OK NEAR INTERSECTION OF DRYLINE AND COLD
   FRONT.
   
   ...WI...
   STRONG FORCING...ELEVATED INSTABILITY AND EFFECTIVE DEEP LAYER SHEAR
   MAY BE FAVORABLE FOR SEVERE HAIL LATER THIS AFTERNOON/EVENING.
   
   ..IMY.. 05/13/2009
   
   .PREV DISCUSSION... /ISSUED 1112 AM CDT WED MAY 13 2009/
   
   ...SYNOPSIS...
   VIGOROUS TROUGH AND STRONG POLAR JET MAX MOVES EWD FROM NRN PLAINS
   TO UPPER GREAT LAKES LATER TONIGHT...WITH GREATEST CONVECTIVE
   POTENTIAL REMAINING ALONG THE SRN PERIPHERY OF THIS SYSTEM WHERE THE
   RESERVOIR OF MOIST/UNSTABLE AIR MASS RESIDES.  COLD FRONT EXTENDS
   FROM THE DEEP LOW WRN ONTARIO SWWD THRU UPPER MS VALLEY...CENTRAL KS
   TO NRN TX PANHANDLE THIS AM.
   
   VERY STRONG SWLY LOW LEVEL JET AOA 60KT FROM SRN PLAINS INTO LOWER
   MO VALLEY CHARACTERIZED BY A PRONOUNCED EML ATOP A VERY MOIST BUT
   RELATIVELY SHALLOW MOIST LAYER. STRONG ISENTROPIC ASCENT UNDERWAY
   ACROSS MID MS VALLEY WITH CURRENT ELEVATED THUNDERSTORMS EXPECTED TO
   CONTINUE AND LIKELY BECOME MORE INTENSE THRU THE AFTERNOON.
   
   ...MID MS VALLEY/LOWER MO VALLEY...
   PERSISTENT ELEVATED THUNDERSTORMS MID MS INTO LOWER OH VALLEYS WILL
   TRANSITION INTO A MORE SURFACE BASED SUPERCELL THREAT BY MID
   AFTERNOON AS TEMPERATURES CLIMB ALONG WITH DEWPOINTS TO THE S AND W
   ACROSS MO INTO SERN KS.  WITH MID LEVEL LAPSE RATES IN EXCESS OF
   8C/KM AND DEWPOINTS RISING THRU THE 60S F...MLCAPES UPWARD OF 2500
   J/KG WILL DEVELOP WITH WEAKENING CINH BY MID AFTERNOON UPSTREAM FROM
   THE ONGOING ELEVATED STORMS.  WHILE DEEP LAYER SHEAR OF 40KT IS NOT
   PARTICULARLY STRONG FOR TORNADIC SUPERCELLS...THE ENHANCED LOW LEVEL
   SHEAR VICINITY OF CONVECTIVE BOUNDARIES WILL LOCALLY ENLARGE
   HODOGRAPHS AND BE QUITE FAVORABLE FOR AT LEAST A COUPLE SUPERCELLS
   CAPABLE OF PRODUCING STRONG TORNADOES BY LATER THIS
   AFTERNOON/EVENING GIVEN THE EXPECTED INSTABILITY. IN ADDITION VERY
   LARGE HAIL SHOULD OCCUR WITH ANY SUPERCELL AND WIND DAMAGE WILL
   BECOME MORE OF A THREAT AS CONVECTION TRANSITIONS INTO MORE OF A
   LINEAR MODE BY THIS EVENING.
   
   ANOTHER FACTOR IN TODAYS CONVECTIVE SCENARIO WILL LIKELY BY THE MCV
   NOW INTO SWRN MO.  AS AIR MASS DESTABILIZES ACROSS SRN MO IN ADVANCE
   OF THIS FEATURE A SEVERE THUNDERSTORM THREAT WOULD LIKELY DEVELOP BY
   MID AFTERNOON.
   
   ...SRN PLAINS...
   STRONG CAP IN PLACE AHEAD OF SEWD ADVANCING COLD FRONT. BY LATER
   THIS AFTERNOON THE FRONT WILL BE A PRIMARY FOCUS OF RAPID
   DEVELOPMENT OF SEVERE THUNDERSTORMS SWRN MO/SERN KS INTO NRN OK
   WHERE A VERY TO EXTREMELY UNSTABLE AIR MASS WILL BE IN PLACE.  AS
   SFC TEMPS ACROSS OK WARM TO AOA 90F WITH DEWPOINTS WELL INTO THE
   60S...MLCAPES WILL CLIMB TO AS HIGH AS 4000 J/KG.  ONCE THE
   COMBINATION OF FRONTAL FORCING AND HEATING IS SUFFICIENT TO WEAKEN
   CAP...SEVERE THUNDERSTORMS INCLUDING SUPERCELLS WILL DEVELOP
   RAPIDLY.  WITH THE THREAT AREA LOCATED ON THE SRN FRINGE OF THE
   STRONG POLAR JET PASSING BY TO THE N...DEEP LAYER SHEAR WILL BE A
   LIMITING FACTOR FOR TORNADOS.  HOWEVER GIVEN THE AMOUNT OF
   INSTABILITY AND LOCALLY ENHANCED LOW LEVEL SHEAR BY EVENING AFTER
   STORMS ARE UNDERWAY...AT LEAST AN ISOLATED TORNADO THREAT IS
   EXPECTED.  HOWEVER VERY LARGE HAIL IS GOING TO BE A PRIMARY CONCERN
   ALONG WITH DAMAGING DOWNBURST WINDS WITH ANY SUPERCELL THAT DEVELOPS
   IN THIS ENVIRONMENT.
   
   A LINEAR MCS WILL THEN DEVELOP SEWD ACROSS MUCH OF OK INTO NRN AR
   TONIGHT WITH A CONTINUED THREAT OF AT LEAST DAMAGING WINDS
   CONTINUING.
   
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