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Mesoscale Discussion 77
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   MESOSCALE DISCUSSION 0077
   NWS STORM PREDICTION CENTER NORMAN OK
   1154 PM CST TUE FEB 17 2015

   AREAS AFFECTED...SRN FLORIDA COASTAL AREAS/KEYS

   CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY 

   VALID 180554Z - 180800Z

   PROBABILITY OF WATCH ISSUANCE...20 PERCENT

   SUMMARY...STORMS DEVELOPING ACROSS THE COASTAL WATERS AND KEYS COULD
   EVENTUALLY BE ACCOMPANIED BY A FEW STRONG SURFACE GUSTS...MAINLY
   TOWARD 09-12Z.  HOWEVER...THE NEED FOR A SEVERE WEATHER WATCH IS NOT
   CURRENTLY ANTICIPATED.

   DISCUSSION...SCATTERED THUNDERSTORM DEVELOPMENT IS NOW WELL UNDERWAY
   ACROSS THE LOWER KEYS...LIKELY IN RESPONSE TO FORCING ASSOCIATED
   WITH WEAK PRE-FRONTAL WARM ADVECTION...AND PERHAPS A WEAK SHORT WAVE
   IMPULSE WITHIN BROADLY CYCLONIC MID/UPPER FLOW.  VARIOUS MODEL
   FORECAST OUTPUT IS SUGGESTIVE THAT THIS INITIAL ACTIVITY WILL
   CONTINUE TO SPREAD NORTHEASTWARD TOWARD SOUTHERN PENINSULA COASTAL
   AREAS...AND THE UPPER KEYS...WITH ADDITIONAL STORM DEVELOPMENT
   OCCURRING ACROSS SOUTHERN COASTAL AREAS AND THE KEYS...ALONG THE
   APPROACHING COLD FRONT...LATER TONIGHT.

   BOUNDARY-LAYER BASED INSTABILITY APPEARS MOSTLY CONFINED TO THE
   COASTAL WATERS AND KEYS...IN ASSOCIATION WITH THE 70F+ SURFACE DEW
   POINTS.  WHILE CAPE IS LIKELY TO REMAIN RELATIVELY WEAK /GENERALLY
   LESS THAN 1000 J PER KG/...DEEP LAYER SHEAR BENEATH 50-60 KT
   WESTERLY 500 MB FLOW IS STRONG...AND MAY CONTRIBUTE TO MID-LEVEL
   UPDRAFT ROTATION IN STRONGEST CELLS.  THE EVOLUTION OF AN
   INCREASINGLY ORGANIZED CONVECTIVE LINE DOES NOT APPEAR OUT OF THE
   QUESTION TOWARD 09-12Z...WHEN PRE-FRONTAL 850 MB FLOW IS FORECAST TO
   VEER FROM SOUTHERLY TO SOUTHWESTERLY...WHILE STRENGTHENING TO 40+ KT
   OR SO.  THIS COULD BE ACCOMPANIED BY AT LEAST SOME RISK FOR STRONG
   CONVECTIVE GUSTS.  HOWEVER...UNTIL THEN...SEVERE WEATHER POTENTIAL
   APPEARS MINIMIZED BY WEAK LOW-LEVEL WIND FIELDS AND SHEAR...IN
   ADDITION TO THE MARGINAL THERMODYNAMIC ENVIRONMENT.

   ..KERR/THOMPSON.. 02/18/2015


   ATTN...WFO...MFL...KEY...

   LAT...LON   24508217 24938161 25238073 25538014 25187995 24768054
               24328180 24508217 

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Page last modified: February 18, 2015
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