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Mesoscale Discussion 64
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   MESOSCALE DISCUSSION 0064
   NWS STORM PREDICTION CENTER NORMAN OK
   0959 AM CST TUE FEB 04 2014

   AREAS AFFECTED...NERN AR/FAR SERN MO/FAR NWRN TN/WRN KY/FAR SRN IL
   AND SWRN IND

   CONCERNING...FREEZING RAIN 

   VALID 041559Z - 042030Z

   SUMMARY...FREEZING RAIN WITH RATES RANGING FROM 0.05-0.1 INCH PER
   HOUR ARE EXPECTED TO DEVELOP NEWD WITHIN A 75-100 MILE WIDE CORRIDOR
   EXTENDING FROM NERN AR TO FAR SRN IL/SWRN IND AND WRN KY.  THIS
   PRECIP-TYPE WILL SPREAD ACROSS NERN AR...FAR SERN MO AND FAR NWRN
   TN/WRN KY THIS MORNING...AND SHOULD REACH FAR SRN IL...FAR SWRN IND
   AND THE REST OF FAR WRN KY AFTER 18Z.

   DISCUSSION...AT 15Z...REGIONAL RADAR IMAGERY SHOWED A RATHER LARGE
   AREA OF PRECIPITATION SPREADING N/NEWD ACROSS AR...WITH LIGHTNING
   DATA INDICATING TSTMS OVER SRN/CENTRAL AR INTO NWRN MS AND ADJACENT
   FAR SWRN TN.  AT THE SURFACE...TEMPERATURES HAVE BEEN RISING SLOWLY
   TO AROUND 32 F OVER NWRN MS INTO SWRN TN WITH THESE OBSERVATIONS
   LOCATED IN THE RELATIVELY WARMER /S-E SIDE/ OF AN INVERTED TROUGH
   WHICH EXTENDED FROM FAR SERN AR TO NWRN TN...THEN ENEWD ALONG THE
   WRN KY/TN BORDER INTO SOUTH CENTRAL KY.  WHILE SURFACE TEMPERATURES
   SHOULD RISE TO ABOVE 32 F IN WRN TN AND PART OF SRN KY INTO THE
   AFTERNOON...NELY SURFACE TRAJECTORIES SUGGEST TEMPERATURES ON THE
   COOL SIDE OF THE INVERTED TROUGH WILL TEND TO REMAIN BELOW 32 F.  

   MOISTENING OF AN INITIALLY RELATIVELY DRY LOWER-MID TROPOSPHERE...
   PER 12Z REGIONAL SOUNDINGS...IS EXPECTED IN THE LOWER OH VALLEY INTO
   THE AFTERNOON.  THIS WILL OCCUR IN RESPONSE TO INCREASING UPWARD
   VERTICAL MOTION WITHIN A CORRIDOR OF STRONG DEEP LAYER ASCENT
   ATTENDANT TO HEIGHT FALLS AHEAD OF THE SRN PLAINS TROUGH AND STRONG
   LOW LEVEL WAA DEVELOPING FROM NERN AR INTO THE LOWER OH VALLEY ALONG
   A 50-60 KT LLJ INTO THE DISCUSSION AREA.  ALTHOUGH SOME GUIDANCE
   SUGGESTS SURFACE TEMPERATURES WILL RISE ABOVE FREEZING INTO THE
   LOWER OH VALLEY LIMITING THE FREEZING RAIN POTENTIAL...THE
   EXPECTATION OF SURFACE TRAJECTORIES REMAINING NELY ON THE COOL SIDE
   OF THE AFOREMENTIONED INVERTED TROUGH RESULTS IN GREATER CONFIDENCE
   THAT SURFACE TEMPS SHOULD REMAIN BELOW 32 F FOR AN EXTENDED PERIOD
   THROUGH THE AFTERNOON.  THUS...THE ELEVATED WARM LAYER ALREADY IN
   PLACE OVER THE DISCUSSION AREA PER 12Z UPPER AIR ANALYSIS WITH THE
   850 MB 0 C ISOTHERM EXTENDING FROM NEAR STL TO SDF AND ADDITIONAL
   LOW LEVEL WAA ATOP THE SUB-FREEZING TEMPS WILL RESULT IN FREEZING
   RAIN BECOMING THE PRIMARY PRECIP-TYPE INTO THE AFTERNOON.  AN
   INCREASE IN PW VALUES TO AROUND 1 INCH SHOULD SUPPORT THE GREATER
   PRECIPITATION RATES INTO THE AFTERNOON.  UNTIL THE COLUMN
   SATURATES...INITIAL PRECIP-TYPES COULD BE A MIX OF SNOW AND/OR
   SLEET...ESPECIALLY WITH NEWD EXTENT INTO THE LOWER OH VALLEY.

   ..PETERS.. 02/04/2014


   ATTN...WFO...LMK...OHX...IND...PAH...ILX...MEG...LSX...LZK...

   LAT...LON   36029124 36929068 37918949 38628776 38458717 37728687
               37288721 36818788 36018895 35669039 35639105 36029124 

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Page last modified: February 04, 2014
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