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Mesoscale Discussion 81
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   MESOSCALE DISCUSSION 0081
   NWS STORM PREDICTION CENTER NORMAN OK
   1022 PM CST FRI FEB 20 2015

   AREAS AFFECTED...PORTIONS OF THE TN AND OH VALLEYS

   CONCERNING...WINTER MIXED PRECIPITATION 

   VALID 210422Z - 211015Z

   CORRECTED FOR REMOVING ERRONEOUS ALERTED WFOS.

   SUMMARY...AREAS OF FZRA...AT TIMES MIXED WITH SLEET AND SNOW LATE
   THIS EVENING...WILL CONTINUE ACROSS THE AREA. ICE ACCRETION RATES UP
   TO 0.05-0.10 IN/HR WILL BE POSSIBLE.

   DISCUSSION...04Z RADAR MOSAIC INDICATES A RELATIVELY LARGE AREA OF
   WINTER MIXED PCPN ACROSS PORTIONS OF THE OH AND TN VALLEYS THIS
   EVENING. THE ERN EXTENT OF THIS REGION IS CHARACTERIZED BY A MIX OF
   PRIMARILY SNOW AND SLEET...WHILE FZRA IS THE PREDOMINANT TYPE
   FARTHER WEST /APPROX BWG-BNA LINE AND VICINITY/. RECENT METARS
   INDICATE THE AREA OF FZRA IS ASSOCIATED WITH ICE ACCRETION RATES
   UPWARDS OF 0.10 IN/HR. 

   IN CONCERT WITH LARGE-SCALE FORCING FOR ASCENT FROM AN APPROACHING
   SHORTWAVE TROUGH ACROSS THE PLAINS...INCREASING ADIABATIC ASCENT
   FROM A 70-KT LLJ WILL PROMOTE ANOTHER ROUND OF PCPN OVERSPREADING
   THE AREA FROM THE WEST AFTER 05-06Z. INDEED...SFC PRES FALLS OF
   1-1.5 MB PER HR ACROSS NE AR /PER 03Z SFC ANALYSIS/ ARE A REFLECTION
   OF THIS ROBUST WAA ALOFT...AND A CONTINUATION OF ICE ACCRETION RATES
   OF 0.05-0.10 IN/HR IS FORECAST THRU APPROXIMATELY 10Z AS MORE FZRA
   SPREADS NORTHEAST ACROSS THE MCD AREA. FURTHERMORE...WHILE NERN
   PORTIONS OF THIS AREA ARE CURRENTLY EXPERIENCING A MIXTURE OF SLEET
   AND SNOW...THE AFOREMENTIONED STRONG WAA SHOULD SUPPORT THESE
   P-TYPES MIXING WITH OR CHANGING OVER ENTIRELY TO FZRA AFTER 06Z. AS
   SUCH...ICE ACCRETION RATES OF SEVERAL HUNDREDTHS OF AN INCH PER HOUR
   CAN BE EXPECTED ACROSS PORTIONS OF CNTRL/ERN KY...NERN TN...AND SRN
   INDIANA LATE TONIGHT AS WELL.

   ..PICCA/EDWARDS.. 02/21/2015


   ATTN...WFO...MRX...JKL...ILN...LMK...OHX...IND...PAH...MEG...

   LAT...LON   36518882 37518858 38308804 38518712 38598634 38618569
               38558513 38188408 37228369 36408395 35748430 35528530
               35468687 35528876 35958895 36518882 

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Page last modified: February 21, 2015
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