MESOSCALE DISCUSSION 2222
   NWS STORM PREDICTION CENTER NORMAN OK
   0354 AM CST SAT DEC 15 2007
   
   AREAS AFFECTED...CNTRL/SRN IND AND SWRN OH
   
   CONCERNING...WINTER MIXED PRECIPITATION 
   
   VALID 150954Z - 151400Z
   
   WATER VAPOR IMAGERY SHOWS THAT THE PRIMARY UPR SYSTEM THAT WILL BE
   RESPONSIBLE FOR A LONG DURATION WINTER EVENT WAS STILL WELL UPSTREAM
   OVER NW TX.  HOWEVER...A BROAD WARM CONVEYOR AHEAD OF THE IMPULSE
   CONTINUED TO TRANSPORT SUBSTANTIAL MOISTURE NWD INTO THE MIDWEST/OH
   VLY THIS MORNING.  SHORT TERM MODELS ARE UNDERESTIMATING THE TIMING
   OF THE FIRST WAVE OF WINTRY MIX...LIKELY RESULTING IN A QUICKER
   ONSET OF PCPN ACROSS THE DISCUSSION AREA.
   
   MAGNITUDE OF WARM ADVECTION WAS ALSO UNDERESTIMATED BY 00Z NAM/21Z
   SREF GUIDANCE...BUT NEWLY ARRIVED 06Z NAM/03Z SREF PACKAGES SEEM TO
   HAVE TRENDS BETTER SAMPLED.  NRN EDGE OF THE HIGHER PCPN RATES WILL
   APPROACH AREAS ALONG/S OF I-70 AND WEST OF I-65 THROUGH 12Z...THEN
   INTO SWRN OH 12-15Z.  SOUNDINGS INDICATE THAT THE COLUMN OVER ECNTRL
   IND/SWRN OH WILL TAKE SEVERAL HOURS TO SATURATE...SO A MID-MORNING
   TIME FRAME FOR HEAVIER PCPN RATES SEEM MORE LIKELY THERE.
   
   FCST THERMODYNAMIC PROFILES...FACTORING IN THE AFOREMENTIONED MORE
   ROBUST WARMING ALOFT...SUGGEST THAT A SN/IP MIX CHANGING TO ZR WILL
   BE LIKELY IN A 45 MILE WIDE STRIP ACROSS SRN IND ROUGHLY CENTERED ON
   A 50 N KEVV-30 E KBMG-30 N KCVG LINE.  PCPN RATES COULD REACH AS
   HIGH AS 0.10-0.20 IN/HR.  FARTHER TO THE N...SN IS MORE LIKELY ALONG
   THE I-70 CORRIDOR FROM KHUF NEWD THROUGH THE INDY METRO AREA TO NEAR
   KMIE.  SRN EDGE OF THE SN BANDS COULD MIX/CHANGE TO IP LATER IN THE
   MORNING.  BUT...SNOWFALL RATES COULD APPROACH 1 IN/HR AT TIMES.
   
   ..RACY.. 12/15/2007
   
   
   ...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...ILN...LMK...IWX...IND...
   
   39988694 40608540 40558478 39928435 39368428 38948458
   38688535 38438612 38558691 38708717 39318748 39838736