Area Forecast Discussion
Issued by NWS Duluth, MN

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436
FXUS63 KDLH 131754
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1154 AM CST Wed Dec 13 2017

.UPDATE...
Issued at 1154 AM CST Wed Dec 13 2017

Please see the 18Z Aviation Discussion below.

UPDATE Issued at 711 AM CST Wed Dec 13 2017

Updated precipitation trends and amounts through this afternoon.
Opted to extend the Winter Weather Advisory into Washburn, Sawyer,
and Price Counties through this afternoon. Also added Bayfield,
Ashland, and Iron Counties, but ran those zones out to 12Z
tomorrow morning to include the bulk of the lake enhanced/lake
effect snow. Still expect another surge of light to briefly
moderate snowfall ahead of the next shortwave which was located
over northwest Ontario and northwest Minnesota at 7 AM. Remainder
of the forecast is on track.

&&

.SHORT TERM...(Today through Thursday)
Issued at 320 AM CST Wed Dec 13 2017

The main forecast challenge for the short-term period is the snow
and wintry mixed precipitation today.

A complex forecast early this morning with several shortwave
troughs expected to move through the Northland today and tonight.
Several periods of wintry mixed precipitation and light snow are
expected. The first shortwave and its fast-moving and strong
clipper system was centered over west-central Minnesota early this
morning and is forecast to quickly advance to near Milwaukee by
noon today. Strong FGEN forcing and height falls with the
shortwave trough have produced a band of light to moderate
precipitation from near Fargo to Remer, MN to Siren, WI as of 215
AM. Forecast soundings indicate a warm/dry layer wrapping into
the low which has supported a wintry mix of rain, freezing rain,
and sleet over northwest Minnesota into portions of central and
north- central Minnesota over the past few hours. The wintry
precipitation should continue for the next several hours and may
begin to taper off by 8 AM. Light snow continued over the
Minnesota Arrowhead and is forecast to slide southeastward this
morning into northwest Wisconsin. With surface and low-level winds
out of the east or southeast over Lake Superior, some orographic
and lake enhanced snow is expected along the North Shore and
interior portions of the Arrowhead. The snow will likely pivot
toward the Twin Ports later this morning and eventually over
northwest Wisconsin by late morning and early afternoon.

Another shortwave trough and vort max will dive south out of
Manitoba this morning resulting in a second round of snow for much
of the Northland late this morning through this afternoon. It`s
possible there won`t be a complete break in the precipitation
between the two shortwaves. The wintry precipitation over portions
of central and east-central Minnesota into northwest Wisconsin
may make roads slippery this morning and result in a slower
commute. Snow accumulation in the Arrowhead and northwest
Wisconsin of 2 to 6 inches is expected today, with lower totals
farther west. Have decided to extend the Winter Weather Advisory
to include Cass, Crow Wing, Aitkin, Pine, and Burnett Counties
where the greatest potential for ice accumulation is located. May
need to extend the Advisory into Bayfield, Ashland, and Iron
Counties for the snow this afternoon. Still have a few hours to
make that decision now that the earlier threat is covered.

Thursday is shaping up drier with light lake effect snow over the
northwest Wisconsin snowbelt and a few snow showers or flurries
in Minnesota. Snow accumulation should be light, less than one-
half inch.

.LONG TERM...(Thursday night through Tuesday)
Issued at 320 AM CST Wed Dec 13 2017

An upper level trof will drop through the forecast area Thursday
night. It`s surface low will remain nearly stationary over eastern
Lake Superior. Winds will be west northwesterly with weak cold
air advection behind the trof. Some light snow will accompany the
trof passage with snow fall amounts less than one inch. As this
upper trof departs, a second trof follows behind, but its track is
farther east and associated with a closed upper low moving
through northwest Ontario. At the surface, a weak surface trof
overlays northwest Wisconsin and the wind remains west northwest
over Lake Superior. This affects the lake effect snow potential.
There are model differences with wind direction over Lake Superior
and will stick with the aforementioned direction, which affects
pops along the Gogebic Range, into north central Wisconsin. Have
low chance pops as a result with little snow amounts. Model
differences become larger Friday night as the NAM features high
pressure, the GFS with a baggy low dropping into western Minnesota
late, and the ECMWF with high pressure over the north, and low
pressure in eastern South Dakota by 12Z Saturday. This is due to a
transition to a more progressive flow aloft and associated pieces
of embedded energy. Higher POPs on Saturday leaning more toward
the GFS. Saturday night finds a positively tilted upper trof
moving through the Northern Plains toward the western Great Lakes.
Followed the GFS here as well with chance pops over the eastern
edge of the forecast area. Will follow the GFS Sunday night
through Tuesday as the model differences remain quite large, and
to keep a bit of consistency.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1154 AM CST Wed Dec 13 2017

A clipper system will quickly skirt southeastward across southern
Wisconsin into the central Great Lakes by this evening. Behind the
clipper, an upper level trough will dig from northern Minnesota
into southern Wisconsin. This will bring MVFR ceilings and
visibilities with brief periods of IFR as snow moves through.

Expect a break in snow late this afternoon and evening at all
sites except HYR, where snow should persist due to lake effect.
Ceilings will remain at MVFR levels per the RAP/NAM/GLAMP
guidance. Another trough will dig into the region from the
northwest late tonight into Thursday afternoon. This will bring
snow showers with MVFR/IFR ceilings and visibilities late tonight
through Thursday morning.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  23   9  18   7 / 100  20  10  20
INL  19   6  15   2 / 100  10  20  30
BRD  24  13  22  11 / 100  10  10  10
HYR  22  10  20   9 / 100  30  20  20
ASX  23  13  21  10 / 100  70  30  40

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until noon CST today for WIZ006.

     Winter Weather Advisory until 3 PM CST this afternoon for
     WIZ007>009.

     Winter Weather Advisory until 6 AM CST Thursday for WIZ002>004.

MN...Winter Weather Advisory until noon CST today for MNZ035-036-038.

     Winter Weather Advisory until 4 PM CST this afternoon for MNZ012-
     020-021.

LS...Small Craft Advisory until 3 PM CST this afternoon for
     LSZ140>143.

     Small Craft Advisory from 6 PM this evening to 2 AM CST Thursday
     for LSZ148.

&&

$$

UPDATE...WL
SHORT TERM...Huyck
LONG TERM...GSF
AVIATION...WL



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