MESOSCALE DISCUSSION 2310
NWS STORM PREDICTION CENTER NORMAN OK
0441 AM CST WED NOV 09 2011
AREAS AFFECTED...PARTS OF NERN IA/SERN MN NORTHEASTWARD THRU MUCH OF
CNTRL WI
CONCERNING...HEAVY SNOW
VALID 091041Z - 091415Z
HEAVY WET SNOW AND GUSTY STRENGTHENING WINDS ARE EXPECTED TO DEVELOP
ACROSS THE REGION THROUGH MID MORNING.
AS A VIGOROUS SHORT WAVE IMPULSE AND ASSOCIATED MID/UPPER JET STREAK
LIFT NORTHEASTWARD ACROSS THE MIDDLE MISSISSIPPI VALLEY TOWARD THE
UPPER GREAT LAKES...RAPID DEEPENING OF AN ASSOCIATED SURFACE CYCLONE
IS NOW UNDERWAY. LATEST SURFACE DATA SUGGEST THAT THIS IS OCCURRING
FASTER THAN PERHAPS MOST MODEL GUIDANCE HAS INDICATED...AND FURTHER
INTENSIFICATION IS EXPECTED AS THE LOW TRACKS FROM WEST CENTRAL
ILLINOIS INTO THE VICINITY OF SOUTHERN LAKE MICHIGAN BY 18Z.
LATEST RUC GUIDANCE SUGGESTS THE DEVELOPMENT OF A NEW DEFORMATION
ZONE...WITH SUBSTANTIAL STRENGTHENING OF MID-LEVEL FRONTOGENETIC
FORCING EXPECTED DURING THE 12-16Z TIME FRAME ALONG AN AXIS NEAR OR
JUST NORTH OF NORTHEASTERN IOWA TOWARD CENTRAL UPPER MICHIGAN.
THERMODYNAMIC PROFILES ACROSS THIS REGION ARE ALREADY MOSTLY BELOW
FREEZING...AND MELTING OF SNOW IS EXPECTED TO CONTRIBUTE TO COOLING
OF THE BOUNDARY LAYER CLOSER TO FREEZING. COUPLED WITH INCREASING
LIFT IN THE FAVORABLE MIXED PHASE LAYER FOR DENDRITIC ICE CRYSTAL
GROWTH...HEAVY SNOW RATES IN EXCESS OF 1 INCH PER HOUR APPEAR
POSSIBLE IN THE PRESENCE OF RELATIVELY HIGH PRECIPITABLE WATER
VALUES AROUND OR ABOVE .5 INCHES.
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