MESOSCALE DISCUSSION 2556
   NWS STORM PREDICTION CENTER NORMAN OK
   0635 PM CST TUE DEC 21 2004
   
   AREAS AFFECTED...S-CENTRAL/SERN MO AND SRN IL
   
   CONCERNING...PRECIPITATION TRENDS...WINTER PRECIPITATION 
   
   VALID 220035Z - 220430Z
   
   MIXED WINTER PRECIPITATION WILL DEVELOP ACROSS S-CENTRAL/SERN MO
   ENEWD INTO SRN IL BETWEEN 03-06Z. INITIAL RAINFALL WILL MIX WITH AND
   GRADUALLY CHANGE TO SNOW FROM NW TO SE...WITH LOCALIZED MOD/HVY SNOW
   POSSIBLE LATER TONIGHT.
   
   AT 22/00Z...SYNOPTIC COLD FRONT EXTENDED FROM CENTRAL IND SWWD
   ACROSS SRN MO INTO CENTRAL OK...WITH SURFACE WET BULB FREEZING LINE
   TRAILING THE BOUNDARY BY 30-40NM. COLD AND RELATIVELY DRY AIR WILL
   CONTINUE TO FILTER SWD ACROSS SRN MO/SRN IL THROUGHOUT THE OVERNIGHT
   PERIOD AS HIGH PRESSURE BUILDS ACROSS THE CENTRAL/NRN PLAINS.
   MEANWHILE...MOIST FLOW FROM THE WRN GULF OF MEXICO CONTINUES TO
   STREAM NWD IN ADVANCE OF SURFACE LOW OVER NERN TX. WARM ADVECTION
   PRECIPITATION WITH EMBEDDED CONVECTION WILL CONTINUE TO INCREASE
   THIS EVENING ACROSS CENTRAL/NRN AR...OVER THE TOP OF A
   QUASI-STATIONARY FRONT EXTENDING NEWD FROM THE SURFACE LOW ACROSS
   CENTRAL AR.  
   
   MID-LEVEL FLOW FIELD IS PROGGED TO BECOME INCREASINGLY FRONTOGENETIC
   ON NRN EDGE OF WARM ADVECTION IN 850-700MB LAYER. THESE TRENDS ARE
   ALREADY UNDERWAY WITH A NOTED INCREASE IN RADAR REFLECTIVITY OVER
   SERN MO/SRN IL IN VICINITY OF MODERATELY STRONG 700MB BAROCLINIC
   ZONE. DRY BOUNDARY LAYER WILL SLOW ONSET OF PRECIP...BUT WILL ALSO
   CONTRIBUTE TO STRONG EVAPORATIVE COOLING AT LOW-LEVELS RESULTING A
   FAVORABLE PROFILES FOR SNOW. COMBINED WITH COLD
   ADVECTION...PRECIPITATION SHOULD CHANGE TO SNOW BETWEEN 03-06Z WITH
   RAIN-SNOW LINE ADVANCING SEWD TOWARD FAR SERN MO AND FAR SRN IL LATE
   TONIGHT. ELEVATED CONVECTION MAY LEAD TO BURSTS OF HEAVY SNOW BY 06Z
   ACROSS THE DISCUSSION AREA AS MARGINAL INSTABILITY AROUND LIT
   /MUCAPE 100 J/KG/ ADVECTS NEWD DURING THE NEXT SEVERAL HOURS.
   
   ..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...PAH...MEG...LSX...SGF...
   
   36509247 36559290 36659306 36849285 37099248 37459183
   37879065 38408924 38418886 38438806 38188803 37738824
   37328872 37168912 36509027