MESOSCALE DISCUSSION 2560 NWS STORM PREDICTION CENTER NORMAN OK 0502 AM CST WED DEC 22 2004 AREAS AFFECTED...EXTREME SERN MO....SRN IL/IND...WRN KY CONCERNING...HEAVY SNOW VALID 221102Z - 221700Z A RELATIVELY NARROW AXIS OF MDT TO HVY SNOW...WITH SNOWFALL RATES APPROACHING 1 INCH PER HOUR...WILL AFFECT THE LWR AND MIDDLE OH RIVER VLY THROUGH THE MORNING. A SW-TO-NE ORIENTED ZONE OF DEEP FRONTOGENESIS WAS SITUATED FROM NRN AR NEWD TO SWRN OH EARLY TODAY AS ARCTIC AIR MASS ACROSS THE UPPER MIDWEST CONTINUES TO UNDERCUT A STRONG LLJ TRANSPORTING ABUNDANT MOISTURE NWD FROM THE GULF/LWR MS VLY. OVERNIGHT...THIS PROCESS HAS RESULTED IN RAIN CHANGING QUICKLY TO MDT TO HVY SNOW FROM SERN MO ACROSS SRN IL AND IND. EXPECT THIS CHANGEOVER...AND AXIS OF HEAVIEST SNOW...TO CONTINUE TO GRADUALLY SPREAD ESE OVER THE NEXT SEVERAL HOURS. MODEL DATA IS IN GOOD AGREEMENT THAT QPF AND THERMODYNAMIC PROFILES IN THE ZONE OF STRONGEST FORCING...GENERALLY ALIGNED ALONG THE LWR/MID OH RIVER VLY...WILL SUPPORT MAXIMUM SNOWFALL RATES OF UP TO 1 INCH PER HOUR UNTIL ABOUT 18Z. LATEST ETA/RUC AND SREF GUIDANCE ALSO SUGGEST THAT INTENSITY OF VERTICAL MOTION WITHIN THIS CORRIDOR WILL BEGIN TO WANE LATER THIS MORNING AS LOW LEVEL JET VEERS AND MID LEVEL FRONTOGENESIS WEAKENS. THUS...MOST INTENSE SNOWFALL WILL NOT ONLY SHIFT GRADUALLY EWD THROUGH THE MORNING...BUT RATES MAY BEGIN TO DIMINISH ACROSS THE ENTIRE AREA BY 18Z. ..CARBIN.. 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...ILN...LMK...IND...PAH...ILX...MEG... 37408695 36788810 36338891 36128945 36259026 37348998 38208896 38838753 39348638 39548518 39208441 38708483 38408524