Tornado Threat
Posted by JAC on 7/29/2011, 5:55 pm



MESOSCALE DISCUSSION 1785
  NWS STORM PREDICTION CENTER NORMAN OK
  0313 PM CDT FRI JUL 29 2011
 
  AREAS AFFECTED...PORTIONS COASTAL S TX.
 
  CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE
 
  VALID 292013Z - 292245Z
 
  TORNADO POTENTIAL...WHILE INITIALLY QUITE MRGL...MAY INCREASE DURING
  REMAINDER AFTERNOON AND EVENING ALONG PORTIONS TX COAST AS CENTER OF
  TS DON NEARS PROJECTED LANDFALL.
 
  PER NHC FCSTS...CENTER SHOULD CONTINUE TO APCH COAST BETWEEN
  BRO-CRP.  ONCE CENTER GETS TO WITHIN ABOUT 20-30 NM OF
  LANDFALL...LEADING PORTION OF MOST KINEMATICALLY FAVORABLE SECTOR OF
  SYSTEM WILL BEGIN TO SPREAD ONSHORE TO ITS N...INCREASING IN
  COVERAGE WITH TIME AS DON TRANSLATES PROGRESSIVELY FARTHER INLAND.
  GRADUAL ENLARGEMENT OF LOW-LEVEL HODOGRAPHS IS EVIDENT IN CRP
  ALREADY...AND WILE STILL TOO SMALL TO SUPPORT SUSTAINED SUPERCELL
  STRUCTURES...IS EXPECTED TO RAMP UP PACE OF INCREASE IN 0-1 KM AGL
  SHEAR FROM NOW THROUGH POST-LANDFALL PHASE.
 
  MAIN LIMITING FACTORS WILL BE
  1. SPATIAL...GIVEN SMALL RADII OF FAVORABLE LOW-LEVEL FLOW/SHEAR IN
  THIS SYSTEM.  THIS WILL GREATLY LIMIT LOW-LEVEL VERTICAL SHEAR
  AVAILABLE TO CONVECTION WELL NE OF CENTER--INCLUDING
  OUTFLOW-DOMINANT/MULTICELLULAR ACTIVITY NOW OBSERVED ACROSS
  MID-UPPER TX COASTAL PLAIN.  SHEAR THERE IS NOT EXPECTED TO INCREASE
  GIVEN PATH OF CENTER PASSING ABEAM/AWAY FROM AREA WITH TIME.
  2. MODAL...WITH LACK OF CONVECTIVE COVERAGE IN REGION OF MOST
  FAVORABLE LOW-LEVEL SHEAR NNW THROUGH SE OF CENTER.
 
  AS SUCH...IT IS NOT YET CLEAR THAT THREAT WARRANTS TORNADO WW...BUT
  WILL CONTINUE TO MONITOR CONVECTIVE AND ENVIRONMENTAL WIND TRENDS
  FOR POSSIBLE ISSUANCE LATER TODAY.
 
  REF NHC ADVISORIES FOR LATEST GUIDANCE ON FCST TRACK/INTENSITY OF
  DON.
 
  ..EDWARDS.. 07/29/2011
 
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When Don belches everyone must be listening - JAC, 7/28/2011, 10:05 pm
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