SWOMCD
SPC MCD 011304
ILZ000-WIZ000-IAZ000-MNZ000-SDZ000-011700-
MESOSCALE DISCUSSION 2173
NWS STORM PREDICTION CENTER NORMAN OK
0704 AM CST SAT DEC 01 2007
AREAS AFFECTED...ERN SD...SRN MN...NRN/ERN IA...NWRN IL
CONCERNING...WINTER MIXED PRECIPITATION
VALID 011304Z - 011700Z
A MIX OF SNOW/SLEET/FREEZING RAIN WILL EXPAND N/EWD THIS MORNING
FROM THE LOWER MO RIVER VALLEY INTO THE UPPER MIDWEST. AREAS OF
MODERATE TO LOCALLY HEAVY SNOW WITH RATES APPROACHING 1 IN/HR WILL
SHIFT NWD ACROSS ERN SD/SRN MN...FOLLOWED BY A TRANSITION TO MIXED
SNOW/SLEET. ACROSS NRN/ERN IA AND NWRN IL...PREDOMINANT PTYPE OF
SLEET WILL TRANSITION TO FREEZING RAIN FROM SW TO NE THROUGH 18Z.
SIGNIFICANT ICE ACCUMULATIONS WILL BECOME LIKELY /REF MCD 2172 FOR
ADDITIONAL INFORMATION PERTAINING TO THIS THREAT ACROSS SRN/WRN IA
AND ERN NEB/.
A SWATH OF WINTERY PRECIPITATION HAS BLOSSOMED ACROSS THE LOWER MO
RIVER VALLEY OVER THE PAST FEW HOURS WHERE A GENERAL N TO S
TRANSITION FROM SNOW TO SLEET TO FREEZING RAIN TO RAIN HAS OCCURRED.
INTENSE WARM/MOIST ADVECTION DRIVEN BY A POTENT LLJ /STRENGTHENING
TO 60 TO 80 KTS AT 850 MB BY 18Z/ WILL FOCUS AMPLE FRONTOGENETICAL
FORCING DOWNSTREAM OF LEAD SHORT WAVE TROUGH ACROSS THE CNTRL/SRN
ROCKIES. THUS...EXPANSION/INTENSIFICATION OF PRECIPITATION
AREA/RATES IS EXPECTED TO CONTINUE. LATEST MODEL GUIDANCE FORECASTS
INDICATE THIS TREND AS WELL...ALTHOUGH THEY MAY BE A BIT TOO BULLISH
WITH QPF ON THE NRN/ERN FRINGE OF THE MD AREA GIVEN AMBIENT DRY
LOW-LEVELS PER 12Z MPX AND DVN RAOBS. NEVERTHELESS...AREAS OF
MODERATE SNOW CENTERED FROM ABR TO FSD SHOULD EXPAND ACROSS MUCH OF
SRN MN...LIKELY REACHING THE I-94 CORRIDOR FROM AXN TO THE TWIN
CITIES METRO TOWARDS 18Z. ACROSS NRN/ERN IA INTO NWRN IL...INITIAL
SNOW SHOULD TRANSITION TO LIGHT/MODERATE SLEET AND EVENTUALLY
FREEZING RAIN AS AN INFLUX OF SATURATED AND WARM LOW-LEVEL
TEMPERATURES /REF 9C TD AT 850 MB IN 12Z TOP RAOB/...CONTINUE TO
ADVECT NEWD ABOVE THE SURFACE-BASED COLD DOME.
.GRAMS.. 12/01/2007
..PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
..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...ILX...MKX...DVN...ARX...MPX...DMX...FGF...FSD...ABR...
44209904 45079816 45729669 45839499 45589367 44419197
43109079 42218987 41098949 40408972 41189126 41569258
42319423 42999604 43009782 43079884 43559910
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