MESOSCALE DISCUSSION 0067
   NWS STORM PREDICTION CENTER NORMAN OK
   1134 PM CST SUN JAN 14 2007
   
   AREAS AFFECTED...PORTIONS CENTRAL/SRN LOWER MI...EXTREME SERN
   WI...EXTREME NWRN OH...EXTREME NRN INDIANA...SRN LM...AND NRN IL.
   
   CONCERNING...WINTER MIXED PRECIPITATION 
   
   VALID 150534Z - 151030Z
   
   MAJOR SFC ICING EVENT POSSIBLE THROUGH 12Z ACROSS PORTIONS
   S-CENTRAL/SERN LOWER MI...EXTREME NRN INDIANA AND NWRN OH...WITH
   FREEZING RAIN CONTINUING THROUGH MUCH OF DISCUSSION PERIOD.  RATES
   LOCALLY EXCEEDING .25 INCH/HOUR ARE POSSIBLE BRIEFLY...WITH .10-.25
   INCH RATES COMMON.  TRANSITION TO LIGHTER FREEZING RAIN RATES IS
   EXPECTED WITH WWD EXTENT ACROSS EXTREME SWRN LOWER MI...SRN LM INTO
   NRN IL...WHERE PRECIP SHOULD WEAKEN FROM SW-NE DURING NEXT 4-6
   HOURS.  MEANWHILE MIXED-PHASE TRANSITION IS EXPECTED FROM FREEZING
   RAIN TO SLEET TO SNOW -- FROM S-N ACROSS S-CENTRAL AND ERN LOWER MI.
   
   
   5Z SFC MESOANALYSIS SHOWED FREEZING LINE NEAR NRN SHORE LE...THEN
   INVOF MI/OH AND MI/INDIANA BORDERS...ARCHING NWD OVER SRN LM...THEN
   WINDING ERRATICALLY SWWD ACROSS NRN IL.  MODIFIED RAOBS AND RUC
   SOUNDINGS INDICATE 5-8 KFT DEEP SUPERFREEZING AIR MASS ABOVE SHALLOW
   NEAR-SFC FREEZING LAYER FROM MI/INDIANA AND MI/OH BORDER REGIONS NWD
   OVER S-CENTRAL/SWRN LOWER MI.  THIS PROFILE GRADUALLY WILL COOL WITH
   TIME...AS APPARENT TOP-DOWN PRECIP COOLING OCCURS IN WARM LAYER
   THROUGH MELTING AND RELATED LATENT HEAT ABSORPTION PROCESSES.  THIS
   WILL MAINTAIN FREEZING RAIN FOR SEVERAL MORE HOURS OVER SERN LOWER
   MI BUT AID IN TRANSITION TO MORE FROZEN PRECIP FARTHER W AND NW. 
   MEANWHILE...WITH BOUNDARY LAYER NEARLY SATURATED...WET BULB COOLING
   EFFECTS NEAR SFC SHOULD BE MINIMAL...AND FREEZING LINE SHOULD MOVE
   LITTLE OVER MOST OF AREA THROUGH REMAINDER OVERNIGHT HOURS. 
   STRONGEST ISENTROPIC ASCENT IN 288-294 K LAYER...AND GREATEST
   FRONTOGENETIC FORCING IN 800-850 MB PRESSURE LAYER...ARE FCST TO
   MOVE NEWD ACROSS REGION THROUGH 9Z...THEN DIMINISH THEREAFTER AS
   BULK OF STRONGEST FORCING SHIFTS EWD OVER SRN ONT AND INTO UPSTATE
   NY.  REF SPC MESOSCALE DISCUSSION 676 FOR MORE DETAILS ON DOWNSTREAM
   FREEZING RAIN POTENTIAL.
   
   ..EDWARDS.. 01/15/2007
   
   
   ...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...CLE...DTX...IWX...GRR...LOT...MKX...DVN...
   
   42948787 43538557 43598409 43868251 43168234 41858309
   41558342 41548499 41678653 42238670 42488728 42028825
   41388844 41528968 41758988