FXUS63 KDLH 091800
AFDDLH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DULUTH MN
1200 PM CST WED DEC 9 2009
.AVIATION...
DEEP LOW PRESSURE WAS OVER MICHIGAN AT 17Z...AND IT WILL CONTINUE
TO MOVE NORTHEAST THROUGH THE PERIOD. SNOW AND BLOWING SNOW
CONTINUED OVER MUCH OF NORTHEAST MINNESOTA AND ALL OF NORTHWEST
WISCONSIN...WITH VSBYS DOWN TO 1 TO 3 MILES OVER NORTHWEST
WISCONSIN...AND WERE EVEN LOWER NEAR THE LAKE SUPERIOR SHORE.
OVERALL...VSBYS WERE HIGHER OVER NORTHEAST MINNESOTA...ESPECIALLY
WEST OF A LINE FROM KBRD TO KHIB TO KCDD. THE SNOW WILL GRADUALLY
DIMINISH FROM WEST TO EAST THIS AFTERNOON AND TONIGHT RAISING VSBYS...BUT
KEEP UP ALONG THE SOUTH SHORE OF LAKE SUPERIOR. MVFR CEILINGS OVER
MUCH OF THE REGION WILL ALSO GRADUALLY INCREASE FROM WEST TO EAST.
GUSTY NORTH TO NORTHWEST WINDS WILL DIMINISH FOR MOST AREAS
THROUGH THE NIGHT.
&&
.PREV DISCUSSION... /ISSUED 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 KTS 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 BAND MAY ALSO AFFECT INTERSTATE 35 IN THE MOOSE
LAKE...BARNUM...WILLOW RIVER AND MAHTOWA AREAS..ESPECIALLY THRU NOON.
&&
.POINT TEMPS/POPS...
DLH 11 -6 7 -5 / 100 40 10 10
INL 3 -14 1 -12 / 60 10 10 10
BRD 7 -10 6 -9 / 80 10 10 10
HYR 17 -4 5 -8 / 100 40 10 10
ASX 20 3 8 -3 / 100 70 20 10
&&
.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.
&&
$$
MELDE/STEWART
