High Risk today N AL, SE TN, N GA
Posted by JAC on 4/27/2011, 5:46 am



DAY 1 CONVECTIVE OUTLOOK CORR 1
  NWS STORM PREDICTION CENTER NORMAN OK
  0110 AM CDT WED APR 27 2011
 
  VALID 271200Z - 281200Z
 
  ...THERE IS A HIGH RISK OF SVR TSTMS OVER PORTIONS OF NRN
  MS...AL...FAR NWRN GA AND SRN MIDDLE TN...
 
  ...THERE IS A MDT RISK OF SVR TSTMS OVER MUCH OF CNTRL AND NRN MS
  AND AL...NWRN GA...MUCH OF TN AND KY...WRN CAROLINAS...
 
  ...THERE IS A SLGT RISK OF SVR TSTMS FROM THE LOWER MS VALLEY/GULF
  COAST STATES NWD TO THE CANADIAN BORDER...
 
  CORRECTED FOR SPELLING ERROR
 
  ...SYNOPSIS...
  AN UPPER TROUGH AXIS WILL BE CENTERED ACROSS THE SRN PLAINS AT 12Z
  WED...WITH A 100 KT MID LEVEL JET ACROSS N TX. THIS FEATURE WILL
  STRENGTHEN THROUGH 00Z AS IT EJECTS NEWD ACROSS THE LOWER MS AND
  INTO THE TN/OH VALLEYS DURING THE DAY. AT THE SURFACE...LOW PRESSURE
  IS FORECAST TO BE OVER W CNTRL AR AT 12Z...WITH A DEVELOPING COLD
  FRONT TRAILING SWWD INTO ERN TX. THESE FEATURES WILL MOVE RAPIDLY
  ENEWD...WITH THE SURFACE LOW NEARING SRN INDIANA BY 00Z AND A SHARP
  LOW PRESSURE TROUGH EXTENDING SWD INTO CNTRL KY...MIDDLE TN...ERN MS
  AND WRN AL.
 
  AHEAD OF THE FRONT...A VERY WARM AND MOIST AIR MASS WILL ALREADY BE
  IN PLACE BY MIDDAY WITH 68-72 BOUNDARY LAYER DEWPOINTS LIKELY FROM
  THE GULF COAST INTO MS/AL...AND MID TO UPPER 60S F OVER TN AND SRN
  KY WHERE SUBSTANTIAL MORNING CONVECTION WILL LIKELY BE ONGOING. WITH
  RELATIVELY COOL TEMPERATURE PROFILES ALOFT...AN EXTREMELY UNSTABLE
  ATMOSPHERE WILL RESULT ACROSS THE WARM SECTOR. WIND FIELDS
  THROUGHOUT THE TROPOSPHERE WILL STRENGTHEN WITH THE APPROACHING
  TROUGH/JET MAX...AND THE COMBINATION OF THE TWO IS EXPECTED TO
  RESULT IN A TORNADO OUTBREAK...WITH LONG-TRACKED STRONG TO VIOLENT
  TORNADOES POSSIBLE OVER THE HIGH RISK AREA.
 
  TO THE E...THE BROAD SLY FLOW ACROSS THE WARM SECTOR WILL EXTEND
  INTO THE MID ATLANTIC REGION...WITH A SECONDARY MOIST PLUME OFF THE
  ATLANTIC NWD INTO THE CAROLINAS AND WRN VA BY AFTERNOON.
 
  --- AN OUTBREAK OF TORNADOES AND DAMAGING WINDS IS EXPECTED TODAY
  THROUGH EVENING OVER PORTIONS OF NRN MS...NRN AL...TN AND KY. ---
 
  ...LOWER MS VALLEY INTO TN/OH VALLEYS...
  A COMPLICATED FORECAST SCENARIO WILL UNFOLD TODAY...BEGINNING RATHER
  EARLY IN THE PERIOD OVER SRN AND ERN AR AND NRN LA. MODELS ARE IN
  RELATIVELY GOOD AGREEMENT WITH THE PLACEMENT OF THE SURFACE LOW OVER
  AR BETWEEN 12-15Z...THEN DEVELOPING IT NEWD ACROSS TN/KY BY 00Z.
  NUMEROUS THUNDERSTORMS WILL BE ONGOING...AND SOME WILL BE
  SEVERE...FROM NRN LA/SRN AR EWD ACROSS NRN MS...WRN AND MIDDLE TN
  AND KY. DESPITE TIME OF DAY...PRESENCE OF RICH LOW LEVEL MOISTURE
  WILL RESULT IN LITTLE CAPPING AND SURFACE BASED EFFECTIVE PARCELS.
  THUS...A TORNADO AND DAMAGING WIND THREAT WILL BE PRESENT WITH THIS
  ACTIVITY.
 
  SOUTH OF THE ONGOING ACTIVITY...STRONG DAYTIME HEATING WILL OCCUR.
  WITH BOUNDARY LAYER DEWPOINTS IN THE LOW 70S F...THIS WILL CREATE
  STRONG TO EXTREME INSTABILITY OVER MS AND AL NWD TO THE ONGOING
  CONVECTION. A CAPPING INVERSION WILL LIKELY KEEP MUCH OF THE WARM
  SECTOR S OF THE EARLY STORMS CAPPED...ALLOWING A BUILD UP OF
  INSTABILITY TO BE RELEASED WHEN LARGE SCALE FORCING ARRIVES DURING
  THE AFTERNOON ALONG THE COLD FRONT AND ESPECIALLY NEAR THE
  FRONT/OUTFLOW BOUNDARY INTERSECTION. THE RESULT WILL BE FAST MOVING
  TORNADIC SUPERCELLS CAPABLE OF STRONG TO VIOLENT TORNADOES. GIVEN
  THE FAST STORM MOTIONS AND RELATIVELY WIDE WARM SECTOR...SOME
  TORNADOES COULD BE LONG LIVED. THE GREATEST THREAT FOR THESE TYPES
  OF STORMS WILL BE OVER THE HIGH RISK AREA...OVER NRN MS AND
  AL...INTO EXTREME NWRN GA AND SRN MIDDLE TN. THIS ACTIVITY WILL
  PERSIST TO THE E...BUT CELLS MAY EVENTUALLY MERGE INTO MORE OF A
  QLCS STRUCTURE CAPABLE OF PARTICULARLY DAMAGING WINDS AND A FEW
  TORNADOES.
 
  ...WRN NC/VA...
  A CONDITIONAL SEVERE THREAT WILL EXIST BY LATE AFTERNOON OVER WRN
  NC/VA.  STRONG  HEATING WILL RESULT IN STEEP LOW LEVEL LAPSE
  RATES...BUT FORECAST SOUNDINGS SHOW A CAPPING INVERSION AROUND 700
  MB...WHICH SHOULD KEEP THE AIR MASS CAPPED. HOWEVER...MOISTURE
  ADVECTION...AS WELL AS SELY UPSLOPE FLOW MAY RESULT IN ISOLATED
  THUNDERSTORMS DURING THE AFTERNOON OVER THE HIGHER TERRAIN. WIND
  PROFILES WOULD FAVOR SUPERCELLS...CAPABLE OF PRODUCING TORNADOES
  HAIL AND WIND. WILL MAINTAIN LOW PROBABILITIES FOR THE DAYTIME
  CONVECTION.
 
  ..JEWELL.. 04/27/2011
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High Risk today N AL, SE TN, N GA - JAC, 4/27/2011, 5:46 am
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