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

   SPC AC 080551
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   1251 AM CDT FRI MAY 08 2009
   
   VALID 081200Z - 091200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS FROM PARTS OF THE S CNTRL
   PLAINS THRU LWR OH AND TENNESSEE VALLEYS....
   
   ...SYNOPSIS...
   MODELS INDICATE THAT SEASONABLY STRONG FLOW WILL PERSIST IN A
   BROAD...GENERALLY ZONAL BELT ACROSS THE NORTHERN AND CENTRAL TIER OF
   THE U.S. THROUGH THIS FORECAST PERIOD.  WHILE THIS REGIME APPEARS
   LIKELY TO REMAIN BROADLY CYCLONIC AT MID-LEVELS...SOME INCREASE IN
   AMPLITUDE APPEARS POSSIBLE AT UPPER LEVELS.  LOW AMPLITUDE RIDGING
   MAY BUILD ACROSS THE NORTHEASTERN STATES...AS LOW AMPLITUDE
   TROUGHING SHIFTS ACROSS THE NORTHERN PLAINS/UPPER MISSISSIPPI
   VALLEY...ASSOCIATED WITH THE EASTWARD PROGRESSION OF THE PRIMARY
   HIGH LEVEL JET CORE TO THE LEE OF THE ROCKIES.  GUIDANCE IS
   SUGGESTIVE THAT THIS COULD BECOME SUPPORTIVE OF SIGNIFICANT SURFACE
   WAVE DEVELOPMENT ACROSS PARTS OF THE UPPER MISSISSIPPI VALLEY INTO
   THE LOWER GREAT LAKES REGION LATER TODAY/TONIGHT...ACCOMPANIED BY A
   COLD INTRUSION TO THE LEE OF THE ROCKIES.
   
   LOW-LEVEL MOISTURE...CHARACTERIZED BY LOWER 70S SURFACE DEW POINTS
   ...HAS ALREADY RETURNED NORTHWARD THROUGH MUCH OF THE CENTRAL/
   SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY.  AND...THE EVOLVING
   PATTERN SEEMS LIKELY TO FAVOR INCREASING PRE-FRONTAL MOISTURE LEVELS
   THROUGH THE REMAINDER OF THE CENTRAL AND EASTERN STATES. 
   HOWEVER...THE PRIMARY CONVECTIVE DEVELOPMENT SEEMS LIKELY TO REMAIN
   FOCUSED ON THE NORTHEASTERN EDGE OF WARM CAPPING ELEVATED MIXED
   LAYER AIR EMANATING FROM THE SOUTHERN U.S./MEXICAN PLATEAU REGION. 
   THERE ARE INDICATIONS THAT THIS COULD BECOME QUITE EXTENSIVE FAIRLY
   EARLY IN THE DAY...ULTIMATELY LIMITING CONVECTIVE POTENTIAL AHEAD OF
   THE MAIN COLD FRONT FROM PARTS OF THE UPPER MISSISSIPPI VALLEY
   THROUGH THE GREAT LAKES INTO PARTS OF THE NORTHEAST.
   
   ...OZARK PLATEAU THROUGH THE LWR OH/TN VALLEYS...
   STRONGER FORCING ASSOCIATED WITH AN IMPULSE SHIFTING EAST OF THE
   CENTRAL ROCKIES IS BECOMING INCREASINGLY EVIDENT IN SATELLITE
   IMAGERY...ON THE SOUTHERN FRINGE OF THE STRONGER WESTERLIES.  THIS
   APPEARS TO PROVIDE SUPPORT FOR THE STRONG SIGNAL AMONG MODEL DATA
   SUGGESTING THE EVOLUTION OF A LARGE MESOSCALE CONVECTIVE SYSTEM
   NEAR/NORTH OF THE KANSAS/OKLAHOMA BORDER INTO SOUTHWEST MISSOURI/
   NORTHWEST ARKANSAS BY 12Z THIS MORNING.
   
   IN THE PRESENCE OF STRONG INSTABILITY AND MODERATE TO STRONG DEEP
   LAYER SHEAR...A SEVERE RISK IN THE FORM OF DAMAGING WINDS/HAIL IS
   EXPECTED TO CARRY OVER BEYOND DAYBREAK.  BUT...OF SIGNIFICANT
   CONCERN TO CONTINUING SEVERE POTENTIAL THROUGH THE MORNING HOURS IS
   SUBSTANTIAL FORECAST WEAKENING OF THE LOW-LEVEL JET AMONG SOME MODEL
   GUIDANCE...INCLUDING THE SREF AND 07/12Z ECMWF.  IF THIS OCCURS...A
   CORRESPONDING WEAKENING OF THE CONVECTIVE SYSTEM MAY
   ENSUE...ACCOMPANIED BY SUBSTANTIAL MODIFICATION OF THE ENVIRONMENT
   ACROSS MUCH OF THE OZARK PLATEAU INTO PARTS OF THE LOWER OHIO AND
   TENNESSEE VALLEYS.
   
   HOWEVER...MODELS MAINTAIN A STRONG CONVECTIVELY ENHANCED OR
   GENERATED MID-LEVEL SPEED MAXIMUM AND CYCLONIC VORTICITY CENTER
   EASTWARD THROUGH THE LOWER OHIO AND TENNESSEE VALLEYS DURING THE
   AFTERNOON AND EVENING HOURS.  IN THE PRESENCE OF A MOIST AND AT
   LEAST MODERATELY UNSTABLE AIR MASS WITH MIXED LAYER CAPE ON THE
   ORDER OF 1000-2000 J/KG...REGENERATION OF CONVECTIVE DEVELOPMENT
   APPEARS PROBABLE.  PROGGED STRENGTHENING OF SOUTHWESTERLY 850 MB 
   FLOW ACROSS KENTUCKY/TENNESSEE DURING THE AFTERNOON COULD YIELD
   LARGE ENOUGH LOW-LEVEL HODOGRAPHS TO SUPPORT THE RISK FOR TORNADOES
   IN MORE DISCRETE ACTIVITY.  BUT...DAMAGING WINDS AND LARGE HAIL ARE
   EXPECTED TO BE A MORE PROMINENT THREAT AS STORM CLUSTERS EVOLVE.
   
   IT IS A DISTINCT POSSIBILITY THAT THE LARGE-SCALE ENVIRONMENT MAY
   REMAIN FAVORABLE FOR THE MAINTENANCE OF THE ANTICIPATED MESOSCALE
   CONVECTIVE SYSTEM AT ITS EARLY MORNING STRENGTH THROUGH MUCH OF THE
   DAY.  IF THIS BECOMES THE CASE...THE SEVERE POTENTIAL ACROSS THE
   OZARK PLATEAU INTO THE LOWER OHIO TENNESSEE VALLEYS MAY BE
   CONSIDERABLY GREATER THAN CURRENTLY DEPICTED IN THE CATEGORICAL
   OUTLOOK.
   
   ...EASTERN PORTIONS OF THE S CNTRL PLAINS...
   A STALLING CONVECTIVE OUTFLOW FROM EARLY MORNING CONVECTION...AND A
   PRE-FRONTAL THERMAL RIDGE...ARE EXPECTED TO PROVIDE THE FOCUS FOR
   POSSIBLE CONVECTIVE DEVELOPMENT LATE THIS AFTERNOON AND EVENING
   ACROSS PARTS OF EASTERN OKLAHOMA...PERHAPS INTO NORTHEAST TEXAS. 
   LOW-LEVEL MOISTURE WILL BE SUPPORTIVE OF STRONG TO EXTREME POTENTIAL
   INSTABILITY IN THE PRESENCE OF STEEP LAPSE RATES...BUT LOWER/MID
   TROPOSPHERIC INHIBITION WILL BE AN ISSUE...GIVEN SOMEWHAT
   WEAK/UNCERTAIN MID-LEVEL FORCING.  AT LEAST ISOLATED TO WIDELY
   SCATTERED STORM INITIATION DOES APPEAR PROBABLE FOLLOWING PEAK
   AFTERNOON HEATING.  IF THIS OCCURS...DEEP LAYER SHEAR WILL BE
   SUFFICIENT FOR SUPERCELLS.  WEAKENING OF LOWER/MID TROPOSPHERIC FLOW
   BY AFTERNOON MAY LIMIT TORNADIC POTENTIAL...DESPITE POTENTIALLY
   FAVORABLE LOW-LEVEL HODOGRAPHS...BUT STRONGEST CELLS WILL BE CAPABLE
   OF AT LEAST PRODUCING VERY LARGE HAIL AND LOCALIZED STRONG DAMAGING
   WIND GUSTS.
   
   ..KERR/JEWELL.. 05/08/2009
   
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   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z