Mike Wilhelm's Alabama Weather Blog

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Bamawx.com

   DAY 2 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   1229 PM CDT THU MAR 26 2009
   
   VALID 271200Z - 281200Z
   
   ...THERE IS A MDT RISK OF SVR TSTMS FRI NIGHT ACROSS PARTS OF SE
   ARKANSAS...NE LOUISIANA....W CNTRL AND NW MISSISSIPPI...AND WRN
   TN....
   
   ...THERE IS A SLGT RISK OF SVR TSTMS FRI/FRI NIGHT...FROM PARTS OF
   THE SERN PLAINS THROUGH THE LWR MS/MID SOUTH AND GULF STATES....
   
   ...SYNOPSIS...
   WITHIN A LINGERING LARGE-SCALE TROUGH THAT ENCOMPASSES MUCH OF THE
   INTERIOR U.S...A STRONG...COLD SHORT WAVE TROUGH IS NOW DIGGING
   THROUGH THE GREAT BASIN AND CENTRAL/SOUTHERN ROCKIES REGION.  MODELS
   CONTINUE TO INDICATE THAT...AS THIS SYSTEM PROGRESSES INTO AND
   THROUGH THE BASE OF THE LARGER SCALE TROUGH LATER TONIGHT INTO
   FRIDAY...IT WILL COME INCREASINGLY IN PHASE WITH A BRANCH OF
   STRONGER UPPER WESTERLIES EMANATING FROM THE SUBTROPICAL PACIFIC. 
   AS THIS OCCURS...MODELS GENERALLY INDICATE THAT AN EMBEDDED LOWER/
   MID TROPOSPHERIC CYCLONE WILL DEEPEN SUBSTANTIALLY...PARTICULARLY
   FRIDAY NIGHT...PROBABLY ACCOMPANIED BY SIGNIFICANT SECONDARY SURFACE
   CYCLOGENESIS FROM PARTS OF THE ARKLATEX THROUGH UPPER PORTIONS OF
   THE LOWER MISSISSIPPI VALLEY.
   
   THIS EVOLVING SYSTEM WILL BE PRECEDED BY COUPLED POLAR AND
   SUBTROPICAL IMPULSES THROUGH  PARTS OF THE MID SOUTH AND
   SOUTHEASTERN STATES EARLY IN THE PERIOD.  WHILE THE INFLUENCE OF
   THESE FEATURES ON CONVECTIVE POTENTIAL IS STILL A SOURCE OF FORECAST
   UNCERTAINTY...THE PRESENCE OF CONSIDERABLE POTENTIAL INSTABILITY
   ACROSS MUCH OF THE GULF OF MEXICO AND GULF STATES SUPPORTS AN
   ELEVATED RISK FOR SEVERE STORMS.  AND...POTENTIAL EXISTS FOR AN
   OUTBREAK OF SEVERE STORMS...INCLUDING THE RISK FOR A FEW STRONG
   TORNADOES AND DAMAGING WINDS...IN ADDITION TO LARGE HAIL.
   
   ...EASTERN GULF STATES...
   A STRONG/SEVERE CLUSTER OF STORMS MAY BE ONGOING ACROSS PARTS OF
   ALABAMA/WESTERN FLORIDA AND GEORGIA EARLY FRIDAY.  BEFORE LARGE-
   SCALE FORCING ASSOCIATED WITH SUPPORTING LEAD UPPER IMPULSES
   WEAKENS/SHIFTS NORTHEASTWARD AND EASTWARD INTO A PROGRESSIVELY MORE
   STABLE ENVIRONMENT...A RISK FOR DAMAGING WINDS...PERHAPS ISOLATED
   TORNADOES...MAY LINGER INTO MIDDAY.
   
   ...SOUTHERN PLAINS THROUGH THE LWR MS VALLEY AND MID SOUTH...
   A CONTINUING RETURN FLOW OFF THE GULF OF MEXICO...BENEATH STEEP
   MID-LEVEL LAPSE RATES ASSOCIATED WITH ELEVATED MIXED LAYER AIR
   ADVECTING EAST NORTHEASTWARD OFF THE MEXICAN PLATEAU...IS EXPECTED
   TO MAINTAIN MODERATE INSTABILITY INTO THIS PERIOD.  CAPE OF
   1000-2000 J/KG IS EXPECTED OVER A FAIRLY BROAD AREA FROM THE
   SOUTHEASTERN PLAINS THROUGH THE LOWER MISSISSIPPI VALLEY/CENTRAL
   GULF COAST REGION.  HOWEVER...MUCH OF THIS INSTABILITY ALONG AND
   EAST OF THE LOWER MISSISSIPPI VALLEY MAY BE BASED ABOVE A SHALLOW 
   STABLE NEAR SURFACE LAYER...NORTH OF A CONVECTIVELY ENHANCED SURFACE
   BOUNDARY LINGERING NEAR THE CENTRAL/EASTERN GULF COAST.
   WITH THE MAIN UPPER FORCING LAGGING TO THE WEST...CONVECTIVE
   POTENTIAL THROUGH MUCH OF THE DAY MAY BE FAIRLY LOW.
   
   AN EXCEPTION MAY BE ALONG A DRY LINE OR PRE-FRONTAL WIND SHIFT
   ACROSS EASTERN TEXAS INTO SOUTHEAST OKLAHOMA...WHERE GUIDANCE
   SUGGESTS STORMS MAY INITIATE AS EARLY AS MIDDAY...IN AN ENVIRONMENT
   FAVORABLE FOR SUPERCELLS.  DESPITE SOMEWHAT MODEST SOUTHERLY
   LOW-LEVEL FLOW...STEEP LAPSE RATES ARE EXPECTED TO BE FAVORABLE FOR
   THE PRODUCTION OF LARGE HAIL AND DAMAGING WIND GUSTS.  AS
   LARGE-SCALE FORCING INCREASES WITHIN THE EXIT REGION OF A STRONG
   MID/UPPER POLAR JET STREAK...AND AHEAD OF AN EASTWARD SURGING COLD
   FRONT...ONE OR MORE BANDS AND CLUSTERS OF STORMS ARE EXPECTED TO
   FORM AND SPREAD NORTHEASTWARD THROUGH THE OZARK PLATEAU.  ACTIVITY
   ALSO SHOULD DEVELOP SOUTHWARD THROUGH THE LOWER MISSISSIPPI VALLEY
   DURING THE LATE AFTERNOON AND EVENING HOURS.
   
   OF PRIMARY CONCERN IS THE DEVELOPMENT AND INTENSIFICATION OF A
   SOUTHERLY LOW-LEVEL JET NEAR THE SECONDARY CYCLONE DURING THE MID/
   LATE EVENING HOURS...WHICH WILL YIELD ENLARGING CLOCKWISE CURVED
   LOW-LEVEL HODOGRAPHS.  THIS IS EXPECTED TO CONTRIBUTE TO INCREASING
   TORNADIC POTENTIAL...INCLUDING THE RISK FOR A FEW STRONG
   TORNADOES...ACROSS PARTS OF SOUTHEASTERN ARKANSAS/NORTHEAST
   LOUISIANA/WEST CENTRAL AND NORTHWEST MISSISSIPPI AND WESTERN
   TENNESSEE BY THE 28/03-06Z TIME FRAME.
   
   RAPID NOCTURNAL WARM SECTOR BOUNDARY LAYER DESTABILIZATION APPEARS
   POSSIBLE...AS STRONG UPPER FORCING...AHEAD OF AN INCREASINGLY
   NEGATIVELY TILTED UPPER TROUGH PIVOTING AROUND THE MID-LEVEL
   CYCLONE.  AND...SEVERAL LINES/CLUSTER OF STRONG/SEVERE STORMS
   CAPABLE OF PRODUCING DAMAGING WINDS/HAIL AND ISOLATED TORNADOES
   APPEAR LIKELY TO SPREAD ACROSS THE LOWER MISSISSIPPI VALLEY/CENTRAL
   GULF COAST AND MID SOUTH FRIDAY NIGHT INTO EARLY SATURDAY.
   
   ..KERR.. 03/26/2009