MESOSCALE DISCUSSION 0181
   NWS STORM PREDICTION CENTER NORMAN OK
   0232 AM CST THU FEB 21 2013
   
   AREAS AFFECTED...FREEZING RAIN AND SLEET
   
   CONCERNING...WINTER MIXED PRECIPITATION 
   
   VALID 210832Z - 211430Z
   
   SUMMARY...FREEZING RAIN RATES WILL INCREASE FROM SW-NE THROUGH THE
   MORNING...WITH 0.10-0.25 INCH ICE ACCUMULATIONS POSSIBLE ON ELEVATED
   SURFACES ACROSS NE OK/NW AR.  PRIMARILY SLEET IS EXPECTED FROM SE KS
   INTO PARTS OF SW MO WHERE THE BOUNDARY LAYER IS COLDER/DEEPER AND
   THE WARM NOSE ALOFT IS LESS PRONOUNCED.
   
   DISCUSSION...A SWATH OF PRECIPITATION IS EXPANDING OVER WRN/NRN OK
   IN A ZONE OF STRONG LOW-LEVEL WAA/FRONTOGENESIS...AS WELL AS
   DIFFERENTIAL CVA IN ADVANCE OF A STRONG SHORTWAVE TROUGH EJECTING
   ENEWD FROM NM.  THE OOZ SOUNDING FROM OUN SHOWED THE DEVELOPING WARM
   NOSE NEAR 800 MB...AND THIS WARMING ABOVE THE SURFACE WILL CONTINUE
   TO SPREAD NEWD WITH TIME.  MEANWHILE...A SHALLOW BOUNDARY LAYER WITH
   TEMPERATURES NEAR FREEZING HAS BEEN MAINTAINED ACROSS NE OK...NRN
   AR...AND SW MO BY AN INFLUX OF CONTINENTAL AIR FROM THE SURFACE
   RIDGE ACROSS THE OH VALLEY.  AS PRECIPITATION RATES INCREASE THROUGH
   THE MORNING...WET BULB COOLING WILL HELP MAINTAIN THE NEAR-FREEZING
   BOUNDARY LAYER...AND THE RISK FOR ACCUMULATING FREEZING RAIN. 
   THOUGH HOURLY RAINFALL RATES COULD EXCEED 0.25 INCHES PER HOUR WITH
   ELEVATED CONVECTION...THE SOMEWHAT MARGINAL SURFACE TEMPERATURES
   SUGGEST THAT SOME OF THE RAINFALL WILL GO INTO RUNOFF PRIOR TO BEING
   ABLE TO FREEZE.  THUS...WHILE ICE ACCUMULATIONS COULD APPROACH 0.25
   INCHES ON VEGETATION AND ELEVATED/EXPOSED SURFACES...THE RISK FOR
   POWER OUTAGES AND MORE SERIOUS ICE ACCUMULATIONS ACROSS NE OK AND NW
   AR WILL BE LIMITED BY THE MARGINAL TEMPERATURES.  SOMEWHAT GREATER
   ICE ACCUMULATIONS WILL BE POSSIBLE ALONG THE TRANSITION ZONE FROM
   FREEZING RAIN TO SLEET ACROSS EXTREME SE KS/SW MO.  
   
   FARTHER N INTO SE KS AND SW MO...THE BOUNDARY LAYER WILL REMAIN
   COLDER/DEEPER WITH A LESS-PRONOUNCED WARM NOSE ALOFT...AS SAMPLED BY
   THE 06Z SPECIAL SOUNDING FROM SGF.  THIS WILL FAVOR SLEET AS THE
   PREDOMINANT PRECIPITATION TYPE...AND THERE WILL BE THE POTENTIAL FOR
   A COUPLE OF INCHES OF SLEET ACCUMULATION GIVEN THE EXPECTED
   PRECIPITATION RATES.
   
   ..THOMPSON.. 02/21/2013
   
   
   ATTN...WFO...LZK...SGF...EAX...TSA...TOP...ICT...OUN...
   
   LAT...LON   38619441 38149346 37519265 36879232 36029215 35469225
               35039255 34929324 35289433 35719541 35899701 36179766
               36529777 37009730 37609643 38039526 38409462 38619441