Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 090554

Area Forecast Discussion
National Weather Service Duluth MN
1154 PM CST Sun Dec 8 2019

Issued at 1153 PM CST Sun Dec 8 2019

Updated for the 06Z Aviation discussion.

UPDATE Issued at 1005 PM CST Sun Dec 8 2019

Despite what the radar says, precipitation southeast of a line
from Aitkin northeast through the Twin Ports is predominantly
freezing drizzle. We have had numerous reports over the past
couple hours of freezing drizzle, and now also reports of roads
becoming slick and hazardous with accidents being reported. Due
to this, have decided to move up the timing of the Winter Storm
Warnings to start as of now, and included mentions of a glaze of
ice developing on area roads, which will then be followed by snow
overnight and Monday morning. Have not reduced snowfall amounts
as this is all in advance of the actual snow, which should start
over the next few hours.

UPDATE Issued at 547 PM CST Sun Dec 8 2019

Lake effect bands are already beginning to set up over parts of
northwest Wisconsin, with snow beginning to move into the western
parts of the forecast area. Forecast looks on track for now, so
little/no change needed to the forecast this evening so far.

Updated for the 00Z Aviation discussion below.


.SHORT TERM...(This evening through Monday night)
Issued at 259 PM CST Sun Dec 8 2019

Not a whole lot of change in this forecast, but the devil is in the
details. The axis of highest QPF has shifted north and west a
smidge, but that puts Duluth and Superior more directly in the
crosshairs of this system and during a period when it will make
travel difficult during the morning commute.

A low pressure system will cross southern Wisconsin and northern
Illinois overnight into Monday morning, this will drape a precip
shield north over our region again, but with much less moisture than
our last big system.  However, there still will be good dendritic
growth potential and winds off the lake which will help enhance
snowfall from Duluth east to the Bayfield Peninsula. Felt confident
enough in these evolutions that the event is too large to cover with
just an advisory, so upgraded to a warning over much of the area.
Snowfall amounts have fluctuated across the Twin Ports in our
graphics materials, but that is mainly an artifact of the binning
being used to create the graphics - something we`ll have to look
into post mortem. Models are in great agreement on the timing of the
most intense snowfall - mainly between midnight and 6 am Monday
across NE MN and between 4 am and noon Monday across NW Wisconsin.
One thing to watch with this storm is there is a good chance for
really deep dendritic growth which could increase snowfalls amounts
locally as this allows snow to pile up quickly - think big
snowflakes. Anyway, most of this system should be out of the region
by Monday afternoon allowing the cold air to pool in. Lows could be
even lower than forecast with all the fresh snow cover.

.LONG TERM...(Tuesday through Sunday)
Issued at 259 PM CST Sun Dec 8 2019

The remnants of the winter storm that is forecast to impact the
Northland tonight and Monday morning will eventually move off to the
east Monday evening. Cold, arctic air will pour into the region
behind the departing system, as well as northwesterly winds, which
will support some lingering lake effect snow across the Lake
Superior snowbelt region. 850 mb temperatures will range between 15
to 18 degrees below zero, leading to sufficiently low 850-water
delta-Ts to support this lake effect. An additional 1 to 2 inches of
snow will be possible over the higher elevations of northern Iron

The main story after the winter storm passes through is the frigid,
arctic temperatures expected for Tuesday and Wednesday as we remain
under cold northwesterly cyclonic flow aloft. 925 mb temperatures
look to range between -19 to -23 degrees C, so a very cold air mass.
Most of the region should remain dry, with the exception for
lingering lake effect possible over far northern portions of Iron
county as the 1000-850 mb mean wind turns more westerly. Wind chills
will become very cold for Tuesday morning and Wednesday morning,
with wind chills ranging from -15 to -30, and -20 to -35,
respectively. So, some bitterly cold mornings are expected.

A high pressure ridge axis will move through the Northland late
Wednesday, which will allow some warmer air to filter into the
region. However, there will be a chance for precipitation Wednesday
night and Thursday morning as a mid-level shortwave passes through.
There is, however, quite a bit of uncertainty as to how much
moisture this system will have, given the differences in QPF among
the deterministic guidance. The ECMWF is coming more in line with
the GFS, which is the most bullish on higher QPF values, but both
the ECMWF and GEM are progging lower QPF than the GFS. Discrepancies
in the models continue into next weekend, so not leaning towards any
particular solution at this time. There does appear to be better
agreement in some warmer temperatures for the late week time frame,
with highs returning into the 20s for Friday.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1153 PM CST Sun Dec 8 2019

An area of snow and IFR/LIFR conditions is moving across the area
as of issuance time. Southeast of the snow is an area of
FZDZ/FZRA with IFR conditions. This will continue to move through
the area, bringing a mixture of IFR/LIFR conditions to all
terminals. KDLH and KHYR to slowly switch to all snow by 09z. The
lowest conditions will be found at KBRD, KDLH, KHIB and KHYR,
with higher conditions to the north. Conditions to begin improving
from the northwest beginning around 15z, continuing until all
sites have returned to VFR by 00z. After 00z all sites should
remain VFR through the remainder of the TAF period.


Issued at 1005 PM CST Sun Dec 8 2019

Strong northeast winds are developing over western Lake Superior,
with speeds of 15 to 25 knots and gusts to around 30 knots, which
are expected to continue overnight tonight through Monday morning
and early afternoon as a low pressure system moves through the
midwest to the south of the area. These winds have produced
building waves and hazardous conditions for small craft, which
will linger through the night before diminishing during the late
morning and afternoon on Monday as winds weaken and turn to the
north. By Monday night and Tuesday winds will be northwest in the
10 to 15 knot range, allowing waves to gradually diminish to less
than 3 feet.


DLH  10  13  -9   1 / 100  90   0   0
INL   0   7 -11  -1 /  90  40  10   0
BRD   8  12 -12   0 / 100  90   0   0
HYR  19  22  -9   4 / 100 100  10   0
ASX  20  22   0   6 / 100 100  50  10


WI...Winter Storm Warning until 6 PM CST Monday for WIZ001>004-

     Winter Weather Advisory until 6 PM CST Monday for WIZ009.

MN...Winter Storm Warning until noon CST Monday for MNZ019-020-025-

     Winter Weather Advisory until noon CST Monday for MNZ010>012-018-

LS...Small Craft Advisory until 4 PM CST Monday for LSZ121-146-147.

     Small Craft Advisory until 3 PM CST Monday for LSZ144-145.

     Small Craft Advisory until 1 PM CST Monday for LSZ142-143.

     Small Craft Advisory until 10 AM CST Monday for LSZ140-141.

     Small Craft Advisory until 10 PM CST Monday for LSZ148.



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