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

   SPC AC 090553
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   1253 AM CDT THU APR 09 2009
   
   VALID 091200Z - 101200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTN AND TONIGHT ACROSS
   PARTS OF THE SRN PLAINS INTO THE OZARK PLATEAU....
   
   ...SYNOPSIS...
   SIGNIFICANT AMPLIFICATION OF A SHORT WAVE TROUGH WITHIN THE SOUTHERN
   BRANCH OF SPLIT POLAR WESTERLIES IS UNDERWAY ACROSS THE EASTERN
   PACIFIC...AND MODELS CONTINUE TO SUGGEST THAT THIS SYSTEM WILL DIG
   INTO THE VICINITY OF THE CALIFORNIA COAST AND BAJA BY 12Z FRIDAY. 
   AS THIS OCCURS...THE LARGE COLD DOWNSTREAM TROUGH IS PROGGED TO
   FINALLY LIFT AWAY FROM THE ATLANTIC SEABOARD.  IN BETWEEN THESE TWO
   FEATURES...AND SOUTH OF A WEAKENING MID-LEVEL CIRCULATION WITHIN
   BROADER SCALE NORTHERN BRANCH RIDGING ACROSS THE NORTH CENTRAL
   STATES...GUIDANCE HAS BEEN CONSISTENT IN INDICATING THAT A
   RELATIVELY COMPACT AND VIGOROUS CLOSED LOW WILL FORM WITHIN THE
   SOUTHERN STREAM TODAY...TO THE LEE OF THE SOUTHERN ROCKIES.  THIS
   FEATURE IS EXPECTED TO EVOLVE FROM THE STRONG SHORT WAVE IMPULSE NOW
   TURNING EASTWARD ACROSS THE FOUR CORNERS STATES...AND IS PROGGED TO
   MIGRATE ACROSS THE SOUTH CENTRAL PLAINS INTO THE OZARK PLATEAU LATER
   TODAY/TONIGHT...ACCOMPANIED BY A DEEP SURFACE CYCLONE WHICH HAS
   ALREADY FORMED TO THE LEE OF THE CENTRAL/SOUTHERN ROCKIES.
   
   DESPITE A FAVORABLE LARGE-SCALE PATTERN FOR RAPID MOISTURE RETURN
   THROUGH THE SOUTHERN PLAINS AND LOWER HALF OF THE MISSISSIPPI
   VALLEY...BOUNDARY LAYER MODIFICATION IN THE WAKE OF THE EASTERN
   TROUGH IS STILL AN ONGOING PROCESS ACROSS THE GULF OF MEXICO AND
   GULF STATES.  AND...IT IS NOT YET CLEAR THAT MOISTENING WILL BE AS
   SUBSTANTIAL AS LATEST NAM FORECASTS OF LOWER/MID 60S SURFACE DEW
   POINTS MIGHT INDICATE.  HOWEVER...GOES BLENDED TOTAL PRECIPITABLE
   WATER DATA DOES INDICATE AT LEAST A NARROW AXIS OF 1+ INCH VALUES
   RETURNING NORTHWARD ALONG THE MEXICAN GULF COAST.  NCEP SREF IS
   SUGGESTIVE THAT THIS WILL RAPIDLY ADVECT NORTHWARD ACROSS EAST TEXAS
   INTO THE OZARK PLATEAU THROUGH THIS PERIOD.
   
   AT THE SAME TIME...WARM ELEVATED MIXED LAYER AIR ADVECTING EAST
   NORTHEASTWARD OFF THE MEXICAN/SOUTHERN U.S. PLATEAU REGION WILL
   CONTRIBUTE TO AIR MASS DESTABILIZATION...WHICH WILL BECOME
   SUPPORTIVE OF INCREASING CONVECTIVE POTENTIAL...INCLUDING THE RISK
   OF SEVERE STORMS...ACROSS THE SOUTH CENTRAL STATES.
   
   ...SOUTH CENTRAL PLAINS INTO THE OZARK PLATEAU...
   A WARM FRONT EXTENDING EAST OF THE SURFACE CYCLONE INTO THE OZARK
   PLATEAU SEEMS LIKELY TO BE THE FOCUS FOR THE MOST WIDESPREAD
   CONVECTIVE DEVELOPMENT TODAY.  MODELS ARE SUGGESTIVE OF STRONG
   CONVERGENCE ALONG THIS BOUNDARY...PARTICULARLY JUST EAST OF THE LOW
   CENTER EXPECTED TO BE MIGRATING ACROSS NORTH CENTRAL OKLAHOMA DURING
   THE LATE AFTERNOON HOURS.  THIS FORCING...COUPLED WITH THAT OF THE
   APPROACH OF THE UPPER IMPULSE...APPEARS LIKELY TO SUPPORT THE
   INITIATION OF STORMS BY OR SHORTLY AFTER 21Z NEAR THE
   KANSAS/OKLAHOMA BORDER AREA.  IN THE PRESENCE OF STEEP LAPSE RATES
   ...AND MIXED LAYER CAPE PROBABLY ON THE ORDER OF 1000 J/KG... LARGE
   CLOCKWISE CURVED LOW-LEVEL HODOGRAPHS WILL BE SUPPORTIVE OF
   SUPERCELLS WITH VERY LARGE HAIL AND A FEW TORNADOES.  THIS ACTIVITY
   IS EXPECTED TO THEN SPREAD EASTWARD AHEAD OF THE SURFACE
   LOW...ACROSS SOUTHEAST KANSAS/NORTHEAST OKLAHOMA INTO SOUTHERN
   MISSOURI/NORTHERN ARKANSAS...WITH LARGE-SCALE FORCING SUPPORTING THE
   GRADUAL CONSOLIDATION AND UPSCALE GROWTH INTO AT LEAST A SMALL
   MESOSCALE CONVECTIVE SYSTEM.  DURING THE EVENING HOURS...THE
   TRANSITION TO MAINLY A DAMAGING WIND THREAT SEEMS PROBABLE... BEFORE
   ACTIVITY SPREADS INTO THE LOWER OHIO/TENNESSEE VALLEYS AND  WEAKENS
   OVERNIGHT.
   
   ALONG THE DRY LINE TRAILING SOUTH OF THE SURFACE LOW CENTER...
   ACROSS PARTS OF EASTERN OKLAHOMA INTO EASTERN TEXAS LATE THIS
   AFTERNOON...MODELS CONTINUE TO INDICATE A RATHER STRONG WESTERLY
   COMPONENT TO THE LOW-LEVEL FLOW JUST OFF THE SURFACE.  AND...
   CONCERN EXISTS THAT THE NEAR SURFACE MOIST LAYER COULD BE SOMEWHAT
   SHALLOW.  EVAPORATIVE COOLING NEAR DOWNDRAFTS COULD TEMPER TORNADIC
   POTENTIAL SOMEWHAT...DESPITE THE GREATER LIKELIHOOD FOR LONGER
   HODOGRAPHS...MORE FAVORABLE FOR CLASSIC LONG-LIVED SUPERCELL TYPE
   STRUCTURES...THAN COMPARED TO THOSE ANTICIPATED ALONG THE WARM
   FRONT.  BUT...A WINDOW OF OPPORTUNITY APPEARS TO EXIST DURING THE
   LATE AFTERNOON/EVENING HOURS FOR SCATTERED DISCRETE STORM
   DEVELOPMENT ACROSS EASTERN OKLAHOMA/NORTHEAST TEXAS INTO WESTERN
   ARKANSAS AND NORTHWEST LOUISIANA.  IF THIS OCCURS... STORMS WILL
   LIKELY BE CAPABLE OF AT LEAST PRODUCING VERY LARGE HAIL AND
   LOCALIZED DAMAGING WIND GUSTS.
   
   ..KERR/GRAMS.. 04/09/2009
   
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   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z