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Mesoscale Discussion 91
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   MESOSCALE DISCUSSION 0091
   NWS STORM PREDICTION CENTER NORMAN OK
   0951 PM CST SUN FEB 22 2015

   AREAS AFFECTED...PORTIONS OF SERN AR...NRN MS...SWRN TN...AND NWRN
   AL

   CONCERNING...WINTER MIXED PRECIPITATION 

   VALID 230351Z - 230745Z

   SUMMARY...A MIXTURE OF FREEZING RAIN AND SLEET WILL CONTINUE TO
   PROGRESS EAST FROM PARTS OF THE LOWER MS VALLEY TOWARDS THE TN
   VALLEY LATE THIS EVENING INTO EARLY TONIGHT. FREEZING RAIN RATES OF
   A FEW HUNDREDTHS OF AN INCH PER HOUR ARE POSSIBLE.

   DISCUSSION...THE 03Z REGIONAL WSR-88D MOSAIC DEPICTS A RELATIVELY
   LARGE AREA OF PCPN STRETCHING EWD FROM THE ARKLATEX TOWARDS THE TN
   VALLEY THIS EVENING. THIS PCPN SHIELD IS PROGRESSING EWD IN RESPONSE
   TO FORCING FOR ASCENT FROM A WEAK SRN STREAM IMPULSE /EVIDENT IN
   EVENING WV IMAGERY/...AS WELL AS ADIABATIC ASCENT ACTING IN CONCERT
   WITH THIS IMPULSE.

   CURRENT KNQA DATA AND THE UPSTREAM 00Z LZK SOUNDING INDICATE A WARM
   NOSE CENTERED AROUND 1.5-2 KM AGL IS ENSURING MELTING OF ICE
   HYDROMETEORS ALOFT ACROSS THE MCD AREA...WITH ONLY A THIN CORRIDOR
   OF SNOW TO THE NORTH. DUAL-POL CC DATA ALSO SUGGEST WAA ALOFT IS OF
   SUFFICIENT STRENGTH TO OFFSET ANY DIABATIC COOLING EFFECTS FROM
   MELTING OF HYDROMETEORS...AS RECENT KNQA DATA INDICATE LESS OF A
   DOWNWARD PERTURBATION OF THE NRN EXTENT OF THE MELTING LAYER OVER
   THE LAST HOUR. THEREFORE...WHILE POCKETS OF SLEET ARE STILL
   EXPECTED...FZRA IS FORECAST TO BECOME THE MORE DOMINANT P-TYPE OVER
   THE NEXT FEW HOURS. IN LOCATIONS FARTHER EAST WHERE SFC TEMPS ARE
   STILL ABOVE FREEZING...N/NELY FLOW WILL SUPPORT CONTINUED COOL/DRY
   AIR ADVECTION. AS SUCH...LOWERING WET-BULB TEMPS WILL COMBINE WITH
   INCREASING SATURATION TO SUPPORT A CHANGEOVER FROM RAIN TO FREEZING
   RAIN THIS EVENING...WITH RATES OF A FEW HUNDREDTHS OF AN INCH PER
   HOUR POSSIBLE.

   ..PICCA/EDWARDS.. 02/23/2015


   ATTN...WFO...OHX...BMX...HUN...MEG...JAN...LZK...

   LAT...LON   33599072 33479165 33739189 34499139 35109028 35188835
               35108737 34818703 34308703 34058725 33728904 33599072 

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Page last modified: February 23, 2015
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