MESOSCALE DISCUSSION 2259
NWS STORM PREDICTION CENTER NORMAN OK
0642 AM CST FRI DEC 01 2006

AREAS AFFECTED...NRN IL...FAR SERN WI...NRN LOWER MI

CONCERNING...HEAVY SNOW

VALID 011242Z - 011715Z

MODERATE TO HEAVY SNOW WILL QUICKLY EXPAND NEWD THROUGH 18Z AS
POTENT UPPER LOW EJECTS RAPIDLY NEWD. SNOWFALL RATES OF 1 TO 2 IN/HR
WILL BE COMMON...WITH THE HEAVIEST BAND OF SNOW FROM PIA NEWD TO
RFD/MKE MOVING ACROSS LK MI INTO W-CNTRL LOWER MI. AN INTENSE
PRESSURE GRADIENT WILL LEAD TO SUBSTANTIAL BLOWING AND DRIFTING
SNOW.

W/V IMAGERY DEPICTS THE UPPER LOW CENTERED NEAR DECATUR IL HAS
ACCELERATED NEWD OVER THE PAST SEVERAL HOURS. PRIMARY SURFACE
CYCLONE NEAR CHAMPAIGN IL HAS RAPIDLY DEEPENED BY 9 MB OVER THE PAST
8 HOURS. 06Z NAM/GFS AND 09Z RUC GUIDANCE ARE VERY SIMILAR IN
TRACKING THE 500 MB LOW TO NEAR DETROIT MI BY 18Z. DEFORMATION BAND
OF MODERATE TO HEAVY SNOW WILL PARALLEL THE TRACK OF THIS LOW FROM
NRN/CNTRL IL AND FAR SERN WI NEWD ACROSS MUCH OF NRN/WRN LOWER MI.
SUBSTANTIAL VERTICAL MOTION WITHIN THE SATURATED DENDRITIC GROWTH
ZONE NW OF PUNCHING DRY SLOT...WILL CONTINUE TO PRODUCE SNOWFALL
RATES AROUND 1 IN/HR. ISOLATED CG LIGHTNING STRIKES WILL ALSO LEAD
TO CONVECTIVE BURSTS OF HEAVY SNOW OF AROUND 2 IN/HR.

ACROSS NRN LOWER MI...12Z APX OBSERVED SOUNDING SHOWS A SUBSTANTIAL
DRY POCKET REMAINS BETWEEN 700 TO 850 MB. HOWEVER...STRONG LOW-LEVEL
ISENTROPIC LIFT AND FRONTOGENETICAL FORCING WILL QUICKLY SATURATE
THE COLUMN. PRONOUNCED UPPER-LEVEL DIVERGENCE/DIFFLUENCE WILL OCCUR
AS 120 KT 500 MB JET SPREADS NEWD ACROSS OH/LK ERIE...AIDING IN
HEAVY SNOW DEVELOPMENT AFTER 15Z.

..GRAMS.. 12/01/2006