Meso Discussion from SPC on Freezing Rain & Sleet

Meso Discussion from SPC

MESOSCALE DISCUSSION 2473
   NWS STORM PREDICTION CENTER NORMAN OK
   0613 PM CST MON DEC 15 2008
  
   AREAS AFFECTED…ARKLATEX TO MIDDLE TN AND CNTRL KY
  
   CONCERNING…WINTER MIXED PRECIPITATION
  
   VALID 160013Z – 160415Z
  
   SHOWERS OF LIGHT FREEZING RAIN/SLEET SHOULD CONTINUE AND GRADUALLY
   SHIFT SEWD…PERHAPS INTENSIFYING THIS EVENING. LIQUID EQUIVALENT
   RATES SHOULD LARGELY RANGE FROM 0.05 TO 0.15/3-HR PERIOD.
  
   REPEATED TRAINING OF SHOWERS WITH LIGHT FREEZING RAIN AND SLEET HAVE
   OCCURRED OVER THE PAST 6-8 HOURS FROM SERN OK INTO WRN
   KY…PRIMARILY DRIVEN BY LOW-LEVEL WARM/MOIST ADVECTION ATOP AN
   ARCTIC FRONTAL ZONE. WITH THE SURFACE FRONT /ANALYZED FROM SRN LA TO
   ERN TN AT 00Z/ EXPECTED TO SLOWLY SAG SWD WITH CONTINUED CAA N OF
   THE BOUNDARY…AXIS OF MIXED PRECIPITATION SHOULD CONCURRENTLY SHIFT
   SWD THIS EVENING. BOTH MORNING AND AFTERNOON NAM/GFS/RUC/SREF
   GUIDANCE HAVE PERFORMED POORLY WITH RESPECT TO QPF PLACEMENT/TIMING
   TODAY. HOWEVER…THEY ARE CONSISTENT WITH STRENGTHING LOW-LEVEL FLOW
   THIS EVENING…WHICH WOULD INCREASE ISENTROPIC LIFT AND PERHAPS LEAD
   TO ENHANCED PRECIPITATION RATES AMONGST WEAK INSTABILITY /AS SAMPLED
   BY 00Z REGIONAL RAOBS/. THIS SCENARIO IS ALSO INDICATED IN 15/00Z
   4-KM WRF-NSSL COMPOSITE REFLECTIVITY…WHICH APPEARED TO HAVE A MORE
   REALISTIC REPRESENTATION OF ONGOING PRECIPITATION….WITH THE
   SUGGESTION OF A GRADUAL SEWD MOVEMENT/INTENSIFICATION OF THE BAND OF
   SHOWERS THROUGH 06Z.
  
   ..GRAMS.. 12/16/2008