MESOSCALE DISCUSSION 2564 NWS STORM PREDICTION CENTER NORMAN OK 1212 PM CST WED DEC 22 2004 AREAS AFFECTED...SERN OK...CENTRAL/NRN AR...FAR SERN MO...FAR SRN IL...FAR WRN KY...WRN/NWRN TN CONCERNING...WINTER MIXED PRECIPITATION VALID 221812Z - 222215Z HEAVY SNOW WILL DEVELOP NEWD FROM SERN OK INTO N-CENTRAL/NRN AR ...FAR SERN MO...FAR SRN IL...AND WRN KY THIS AFTERNOON INTO EARLY THIS EVENING. FREEZING RAIN AND SLEET IS LIKELY MUCH OF THIS AFTERNOON FROM CENTRAL AR ENEWD INTO SWRN TN. AT 1730Z...ELONGATED FRONTAL ZONE EXTENDED FROM PARENT CYCLONE OVER WRN QUEBEC SWWD ACROSS THE OH/TN VALLEYS TO A SECONDARY LOW NEAR THE TX UPPER COAST. THIS LOW WILL TRACK NEWD TO SWRN MS BY 00Z...WITH CONTINUED ADVECTION OF DRY POLAR LOW-LEVEL AIR ACROSS THE SRN PLAINS EWD INTO THE MID-MS RIVER VALLEY. IMPRESSIVE 500MB TROUGH AND ASSOCIATED 80KT JET MAX WILL ROTATE EWD ACROSS NRN/CENTRAL TX THROUGH 00Z. COUPLED 300MB JET STRUCTURE BECOMES WELL ESTABLISHED ACROSS AR NEXT SEVERAL HOURS...AS DOES MID-LEVEL PVA LEADING TO DEEP LAYER VERTICAL MOTION FROM SERN OK NEWD ACROSS CENTRAL/NRN AR INTO THE LOWER OH RIVER VALLEY BY EARLY TONIGHT. IN ADDITION...SYSTEM IS TAPPING AMPLE GULF MOISTURE AND MARGINAL INSTABILITY LEADING TO IMPRESSIVE PRECIPITATION SHIELD THAT SHOULD EXPAND NWD OVER SUBFREEZING AIR ACROSS NRN AR EWD TO WRN KY DURING NEXT 6 HOURS. FRONTOGENETIC FORCING IS PROGGED TO BECOME BETTER ESTABLISHED NEWD FROM UPPER TROUGH ACROSS NRN AR INTO FAR SERN MO AND NWRN TN/WRN KY LEADING TO REDEVELOPMENT OF MODERATE TO HEAVY SNOW ACROSS ERN PORTIONS OF THIS AXIS LATE THIS AFTERNOON INTO EARLY EVENING. SNOW RATES OF 1"/HR APPEAR LIKELY ACROSS THIS REGION FOR AT LEAST SEVERAL HOURS. STRENGTHENING ISENTROPIC ASCENT ACROSS CENTRAL AR INTO WRN TN SHOULD RESULT IN FAVORABLE PROFILES FOR FREEZING RAIN OR SLEET THIS AFTERNOON FROM LIT EWD TO MEM AND ADJACENT AREAS JUST TO THE NORTH. 18Z SOUNDING FROM LIT INDICATES ABOVE FREEZING LAYER FROM 850-750MB. SHALLOW NEAR-SURFACE COLD ADVECTION IS LIKELY...HOWEVER...COOLING ALOFT IS UNLIKELY UNTIL MID-LEVEL TROUGH MOVES OVERHEAD EARLY THIS EVENING. RUC SOUNDINGS THIS AFTERNOON INDICATE ELEVATED INSTABILITY WHICH SHOULD RESULT IN HEAVY FREEZING RAIN/SLEET AND POSSIBLE THUNDERSTORMS. DESPITE INTENSE PRECIPITATION RATES...MARGINAL GROUND TEMPERATURES MAY LIMIT EXTENT OF SURFACE ICING ALTHOUGH SOME THREAT SHOULD EXIST ON ELEVATED ROADS AND STRUCTURES. ..BANACOS.. 12/22/2004 ...NOTICE... SPC WINTER WEATHER MESOSCALE DISCUSSIONS WILL BE ISSUED ON A SCHEDULED BASIS...FOUR TIMES A DAY...BETWEEN 00-01 UTC... 06-07 UTC...12-13 UTC...AND 18-19 UTC AS SIGNIFICANT SHORT RANGE WINTER WEATHER EVENTS UNFOLD. THIS SCHEDULE WILL BE USED FROM DECEMBER 1 THROUGH FEBRUARY 28. ATTN...WFO...OHX...PAH...MEG...LZK...SGF...SHV...TSA... 35979293 36958989 37478839 37168766 36438772 36188778 35508897 35048992 34729061 34349176 34159374 33919477 33899515 34079537 34549530 35349432 35939295