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Mesoscale Discussion 69
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   MESOSCALE DISCUSSION 0069
   NWS STORM PREDICTION CENTER NORMAN OK
   0909 AM CST MON FEB 16 2015

   AREAS AFFECTED...A LARGE PART OF TN

   CONCERNING...WINTER MIXED PRECIPITATION 

   VALID 161509Z - 162015Z

   SUMMARY...FREEZING RAIN AND SLEET WILL CONTINUE SUPPORTING
   SUBSTANTIAL ICING ACROSS MUCH OF TN INTO THE AFTERNOON...WITH THE
   PRECIPITATION SPREADING EWD WITH TIME.

   DISCUSSION...SFC OBSERVATIONS ARE INDICATING WIDESPREAD SLEET AND
   FREEZING RAIN ASSOCIATED WITH A CONTINUOUS SHIELD OF PRECIPITATION
   EXTENDING FROM THE MID-SOUTH REGION TO MIDDLE TN. WITH NQA AND OHX
   VWPS DEPICTING NOTABLE VEERING OF WIND DIRECTION WITH HEIGHT IN THE
   LOWER TROPOSPHERE...WAA IS STRONG ACROSS THE AREA. RELATED STRONG
   ISENTROPIC ASCENT WILL CONTINUE IN PROXIMITY TO A LLJ THAT WILL
   GRADUALLY SHIFT EWD INTO THE AFTERNOON...WITH THE
   ASCENT/PRECIPITATION SPREADING TOWARD THE APPALACHIANS.

   THE 12Z BNA RAOB SAMPLES AN ELEVATED WARM LAYER JUST ABOVE H85
   SURMOUNTING DEEP SUB-FREEZING AIR...SUPPORTING SLEET.
   HOWEVER...ELEVATED WAA-ENHANCED WARMING WILL ALSO HAVE A PROPENSITY
   TO MELT DESCENDING HYDROMETEORS TO SUPPORT AREAS OF FREEZING RAIN
   ACROSS THE REGION...AND LOCAL-AREA/UPSTREAM OBSERVATIONS SUGGEST
   FREEZING RAIN RATES OF 0.05-0.10 INCH PER HOUR THIS MORNING. SLEET
   ACCUMULATION RATES MAY REACH NEAR A QUARTER INCH PER HOUR.
   SUBSTANTIAL ICING WILL LIKELY RESULT FROM THESE FREEZING RAIN/SLEET
   RATES...ESPECIALLY IN ANY CONVECTIVE ELEMENTS.

   SHORT-RANGE FORECAST SOUNDINGS DO INDICATE NEAR-SFC WARMING
   SUPPORTING A TRANSITION TO PURE LIQUID RAIN ACROSS SRN PARTS OF
   MIDDLE AND SERN TN THIS AFTERNOON. HOWEVER...OBSERVATIONS SHOW A
   VERY DRY AIR MASS IN PLACE -- AS REPRESENTED BY SFC DEWPOINTS FROM
   THE UPPER SINGLE DIGITS TO THE TEENS -- AND RELATED WET-BULB COOLING
   MAY OFFSET SFC-LOW PRECEDING WAA AND VERY MODEST DIURNAL HEATING. AS
   SUCH...IT IS POSSIBLE THAT FROZEN PRECIPITATION MAY PREDOMINATE
   REGION-WIDE. ELSEWHERE...PRECIPITATION WILL BEGIN TAPERING OFF FROM
   WEST TO EAST ACROSS PARTS OF THE MID-SOUTH BY MID-AFTERNOON...AS
   LARGE-SCALE ASCENT SHIFTS EWD.

   ..COHEN.. 02/16/2015


   ATTN...WFO...MRX...OHX...HUN...MEG...

   LAT...LON   35768956 36248858 36548687 36538493 36498293 35798364
               35158521 35048822 35089005 35768956 

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Page last modified: February 16, 2015
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