FXUS63 KDLH 091506 AAA
AFDDLH

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE DULUTH MN
906 AM CST WED DEC 9 2009

.MESOSCALE UPDATE...CONCERNING THE MESOSCALE HEAVY SNOW BAND SETTING 
UP FROM MOOSE LAKE TO DULUTH...TO TOFTE...
 
DEEP 977MB SURFACE LOW HAS LIFTED TO SRN LAKE MICHIGAN THIS 
MORNING..LOCATED JUST NORTHEAST OF MILWAUKEE AT 830 AM.  INTENSE 
PRESSURE GRADIENT IS RESULTING IN STRONG NORTH WINDS ACROSS MOST OF 
THE FORECAST AREA..WITH A GRADUAL BACKING IN DIRECTION OF 10 TO 30 
DEGREES NOTED OVER THE PAST COUPLE OF HOURS.

OVERALL SYNOPTICALLY FORCED SHIELD OF PRECIPITATION HAS EXHIBITED A 
WEAKENING TREND OVER THE PAST COUPLE HOURS..BUT A DISTINCT MESOSCALE 
BAND OF MODERATE TO HEAVY SNOW /KDLH REFLECTIVITY VALUES FROM 25-35 
DBZ/ HAS RAPIDLY ORGANIZED SINCE 730 AM FROM MOOSE LAKE 
NORTHEASTWARD TO THE DULUTH/SUPERIOR HARBOR AND THEN PARALLEL TO THE 
NORTH SHORE AS FAR NORTHEAST AS TOFTE.  BAND DEVELOPMENT HAS BEEN 
COINCIDENT WITH THE LOW LEVEL FLOW BACKING TO A SLIGHTLY MORE N/NNW 
DIRECTION.

THIS MESOSCALE SNOWBAND APPEARS TO BE THE RESULT OF A FORCED GRAVITY 
WAVE IN THE LEE OF THE NORTH SHORE TERRAIN RIDGE.  TYPICALLY..THIS 
BAND SETS UP A BIT FARTHER EAST THAN OBSERVED THIS MORNING..BUT DUE 
TO THE LOW LEVEL FLOW BEING MORE NORTHERLY /INSTEAD OF 
NORTHWESTERLY/..AND THE LOW LEVELS BEING EXTREMELY STABLE..IT HAS 
SET UP CLOSER TO THE TERRAIN RIDGE.

CROSS SECTIONS FROM THE RUC MODEL THIS MORNING INDICATE A VERY 
STRONG INVERSION WITH 30-40 KNTS OF 925 FLOW ACROSS THE RIDGE AXIS 
BELOW THE INVERSION..IDEAL FOR BOTH SURFACE AND INTERNAL GRAVITY 
WAVE GENERATION..WITH SLOW WAVE PROPAGATION UPSTREAM TO THE 
NORTHWEST WITH TIME.  THIS PRECIP BAND WILL LIKELY PERSIST IN SOME 
FORM UNTIL THE UPSTREAM RADAR ECHOES PULL EAST OF THE NORTH SHORE 
RIDGE..WHICH ACCORDING TO SHORT RANGE MODEL GUIDANCE MAY BE LATE 
AFTERNOON.

IN THE MEAN TIME..WE EXPECT THIS SNOWBAND TO SLOWLY MIGRATE TO THE 
NORTHWEST WITH TIME..WHILE PRODUCING 1/2 TO 1 INCH PER HOUR SNOWFALL 
RATES. THIS MAY RESULT IN ADDITIONAL SNOW ACCUMULATIONS SEVERAL 
INCHES GREATER THAN PREVIOUSLY EXPECTED UNDERNEATH THE NARROW BAND.  
THE SW END OF THE BADN MAY ALSO AFFECT INTERSTATE 35 IN THE MOOSE 
LAKE...BARNUM...WILLOW RIVER AND MAHTOWA AREAS..ESPECIALLY THRU NOON.

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
MN...WINTER WEATHER ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR MNZ012-
     019-034>036.

     WINTER STORM WARNING UNTIL MIDNIGHT CST TONIGHT FOR MNZ020-021-
     037-038.

WI...WINTER STORM WARNING UNTIL MIDNIGHT CST TONIGHT FOR WIZ006>009.

     WINTER STORM WARNING UNTIL 6 AM CST THURSDAY FOR WIZ001>004.

LS...SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 6 PM CST THURSDAY 
     FOR LSZ121-140>148.

     GALE WARNING UNTIL 6 PM CST THIS EVENING FOR LSZ121-140>148.

&&

$$
 MILLER