MESOSCALE DISCUSSION 2212
   NWS STORM PREDICTION CENTER NORMAN OK
   0104 AM CST WED DEC 12 2007
   
   AREAS AFFECTED...NWRN TX...SWRN/SCENTRAL OK
   
   CONCERNING...WINTER MIXED PRECIPITATION 
   
   VALID 120704Z - 121300Z
   
   INCREASING PRECIPITATION OVER NWRN/WCENTRAL TX WILL EXPAND NEWD AND
   BEGAN ENCOUNTERING SUB-FREEZING SFC AIRMASS OVER NWRN TX/SWRN AND
   SCENTRAL OK BETWEEN 09-12Z. A MIX OF SLEET/FREEZING RAIN IS EXPECTED
   WITH HRLY LIQUID ACCUMULATION RATES UP TO 0.10 INCH IN CONVECTIVE
   SHOWERS.
   
   LATEST RADAR IMAGERY SHOWS PRECIPITATION EXPANDING OVER
   WCENTRAL/NWRN TX FROM NORTH OF ABI SWD TO NEAR SJT. THIS
   PRECIPITATION WAS DEVELOPING IN RESPONSE TO APPROACHING UPPER JET
   OVER SWRN TX AND STRENGTHENING MID LEVEL FRONTOGENESIS/WAA IN THE
   800-600 MB LAYER. STEEP MID LEVEL LAPSE RATES IN THIS LAYER WILL
   SUPPORT CONVECTIVE NATURE OF THE PRECIPITATION. ALTHOUGH THE SFC
   FREEZING LINE WAS WELL NORTH OF THE PRECIPITATION AREA
   PRESENTLY...CONTINUED MODERATE LOW LEVEL CAA WILL SUPPORT A SWD
   MOVEMENT OF THE FREEZING LINE. SUB-FREEZING TEMPERATURES ARE
   EXPECTED TO REACH A KNOX COUNTY TX TO MURRAY COUNTY OK LINE BY 12Z.
   AS THE DEVELOPING PRECIPITATION MOVES NEWD ACROSS NWRN TX AND
   SWRN/SCENTRAL OK AND MOVES ACROSS THE SUB-FREEZING SFC AIR...A
   SUFFICIENTLY DEEP WARM/DRY LAYER WILL EXIST BENEATH 800 MB TO
   SUPPORT A MIX OF FREEZING RAIN/SLEET. GIVEN THE DEPTH OF THE DRY
   LAYER /AROUND 100 MB/...PRECIPITATION RATES ARE GENERALLY NOT
   EXPECTED TO BE VERY HIGH INITIALLY. HOWEVER...WHERE CONVECTIVE
   SHOWERS MOVES ACROSS...FREEZING RAIN RATES UP TO 0.10 IN/HR WILL BE
   POSSIBLE BY 12Z.
   
   ..CROSBIE.. 12/12/2007
   
   
   ...NOTICE...
   SPC WINTER WEATHER MESOSCALE DISCUSSIONS WILL BE ISSUED ON A
   SCHEDULED BASIS FROM DECEMBER 1 THROUGH FEBRUARY 28...FOUR
   TIMES A DAY...AROUND 00 UTC...06 UTC...12 UTC...AND 18 UTC
   FOR SIGNIFICANT SHORT RANGE WINTER WEATHER EVENTS.
   
   ATTN...WFO...FWD...OUN...SJT...LUB...
   
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