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Mesoscale Discussion 67
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   MESOSCALE DISCUSSION 0067
   NWS STORM PREDICTION CENTER NORMAN OK
   0257 AM CST MON FEB 16 2015

   AREAS AFFECTED...NERN OK/SRN MO/SRN IL/SRN INDIANA/WRN AND CENTRAL
   KY/WRN AND MIDDLE TN/AR/NRN MS/NWRN AL

   CONCERNING...WINTER MIXED PRECIPITATION 

   VALID 160857Z - 161500Z

   SUMMARY...A WIDESPREAD AREA OF WINTRY PRECIPITATION -- INCLUDING
   HEAVY SNOW ACROSS MO/SRN IL/SRN INDIANA AND KY...MIXED PHASES ACROSS
   NRN AR/FAR SERN MO AND PARTS OF NRN TN...AND MAINLY FREEZING RAIN
   ACROSS CENTRAL AND SRN AR/NRN MS/NWRN AL AND INTO SRN TN -- WILL
   CONTINUE THROUGH THIS MORNING.  HEAVY SNOW ACCUMULATIONS ARE LIKELY
   ACROSS NRN PORTIONS OF THE DISCUSSION AREA...WITH SUBSTANTIAL
   FREEZING RAIN ACCUMULATIONS OVER SRN PORTIONS OF THE AREA.

   DISCUSSION...A STRONG LOW-LEVEL BAROCLINIC ZONE CONTINUES TO TIGHTEN
   ACROSS THE SRN PLAINS/MID MS/TN VALLEY REGION EARLY THIS MORNING. 
   THIS BAROCLINIC ZONE LIES AT THE INTERSECT OF SURFACE HIGH PRESSURE
   AND AN ASSOCIATED POLAR/ARCTIC AIRMASS SPILLING SEWD OUT OF CANADA
   INTO THE PLAINS/MIDWEST/NERN STATES...WHILE PRONOUNCED ADVECTION OF
   HIGHER THETA-E LOW-LEVEL AIR CONTINUES ACROSS TX/THE LOWER MS
   VALLEY/GULF COASTAL STATES.  

   THIS BACKGROUND SCENARIO IS UNFOLDING DUE TO A BRIEF TRANSITIONAL
   STAGE OF THE ERN U.S. LONG-WAVE TROUGH...AS A STRONG/SMALLER-SCALE
   TROUGH/LOW MOVES OUT OF THE NERN U.S. INTO THE CANADIAN MARITIMES
   AND A SECOND/REINFORCING TROUGH DIGS SEWD OUT OF CANADA AND ACROSS
   THE NRN INTERMOUNTAIN REGION.  BETWEEN THESE TWO SYSTEMS...A BRIEFLY
   MORE ZONAL/WLY FLOW FIELD ALOFT IS MANIFESTING OVER THE S CENTRAL
   AND SERN CONUS.  

   AS THE WRN TROUGHING DIGS SEWD...SURFACE CYCLOGENESIS OVER THE S
   CENTRAL U.S. ALONG THE AFOREMENTIONED BAROCLINIC ZONE IS YIELDING A
   ZONE OF STRONG WARM ADVECTION -- DRIVING THE ISENTROPIC ASCENT AND
   RESULTING WINTRY PRECIPITATION EVENT THAT IS ONGOING.  WHILE
   MIXED-PHASE PRECIPITATION IS INDICATED ACROSS A SIZABLE PORTION OF
   THE DISCUSSION AREA ATTM -- IN PART DUE TO CONVECTIVE NATURE OF THE
   PRECIPITATION...CURRENT THINKING IS THAT THE BAND OF HEAVIEST
   SNOWFALL -- WITH RATES OF 1-2" PER HOUR -- WILL OCCUR FROM NERN OK
   ENEWD ACROSS NWRN AR AND SRN MO...AND EWD INTO SRN IL/WRN KY.  WITH
   TIME...EWD EXPANSION OF THE HEAVY SNOW BAND IS EXPECTED TO
   CONTINUE...SPREADING INTO SRN INDIANA AND CENTRAL/WRN KY WITH TIME.

   FARTHER S -- A ZONE OF MIXED-PHASE PRECIPITATION WILL PERSIST --
   MAINLY ACROSS NRN AR AND PARTS OF WRN TN.  HOWEVER...A TRANSITION TO
   PRIMARILY SNOW IS EXPECTED TO GRADUALLY OCCUR LATER THIS MORNING
   OVER WRN PORTIONS OF THIS AREA...I.E. NWRN AR...AS THE EVOLVING
   SURFACE LOW -- AND PRECEDING ZONE OF STRONGEST WARM ADVECTION --
   SHIFTS EWD OUT OF TX AND ACROSS THE LOWER MS VALLEY WITH TIME. 
   ACROSS SRN PORTIONS OF THE AREA -- INCLUDING PARTS OF CENTRAL AND
   SRN AR/NRN MS/NWRN AL AND SRN TN...SUBSTANTIAL FREEZING RAIN
   ACCUMULATIONS ARE EXPECTED TO CONTINUE.  WHILE ERN PORTIONS OF THE
   AFOREMENTIONED AREA -- I.E. NERN MS/NWRN AL/SRN MIDDLE TN -- REMAIN
   ABOVE FREEZING...DEWPOINTS IN THE SINGLE DIGITS SUGGEST SUBSTANTIAL
   WET-BULB COOLING IS LIKELY -- SUPPORTING THE EXPECTATION THAT
   FREEZING RAIN WILL PREDOMINATE ACROSS THESE AREAS INTO THE
   MID-MORNING HOURS.

   ..GOSS/CORFIDI.. 02/16/2015


   ATTN...WFO...MRX...JKL...ILN...LMK...OHX...IND...BMX...HUN...
   PAH...MEG...JAN...LSX...LZK...SGF...SHV...TSA...ICT...

   LAT...LON   34869487 35689629 36409657 36999603 38139163 38328983
               38438435 38108318 37068337 35908535 34468682 33988864
               33759199 34229402 34869487 

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