Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 180546
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1146 PM CST Sat Feb 17 2018

.UPDATE...

Updated aviation section below for 06Z TAF TAF issuance.

Issued at 932 PM CST Sat Feb 17 2018

The evening model runs have been showing an interesting trend for
tomorrow`s snowfall event. The high-resolution models that have
been arriving are reinforcing a slightly more northerly track on
the frontogenesis band, focusing the snow band on an area from
northern Itasca county east to the north shore betwen Silver Bay
and Taconite Harbor. On top of it, we have a fairly strong
easterly flow setting up off Lake Superior, which is going to
enhance snowfall amounts, especially along the immediate north
shore areas. Thus, have decided to upgrade the watch to an
advisory and warning, with the warning mainly for the north shore
and inland as far as the Hibbing area, where both lake moisture
contributions and upslope will enhance snowfall amounts. I
suspect that we could get these higher snowfall even farther west
due to the strength of the frontogenesis band and the snow
ratios, but have held off pushing up those snowfall amounts and
putting the warning farther west for now, and will leave it for
one more re- evaluation before the snow starts.

&&

.SHORT TERM...(This evening through Sunday)
Issued at 251 PM CST Sat Feb 17 2018

A cold front was moving through the forecast area at 1930Z. Some low
and mid clouds have formed behind the front over much of northeast
Minnesota. Last of the low stratus was moving out of Price County. A
mainly clear sky is expected through the evening with surface
ridging covering the region. Late tonight, the ridging moves over
eastern Lake Superior, while a closed mid level circulation moves
out of eastern Montana into the Northern Plains by 12Z Sunday.
Meanwhile, its surface reflection reaches western South Dakota.
Still expecting snow to develop ahead of this system and reach the
southwest quad of the forecast area after 09Z. Models have com into
better agreement with this onset of the snow, including the short
term hires models. The ARW/NMM/GEM are a bit strong/fast with some
moderate snow bands well into the St. Croix River valley by 12Z
Sunday. Prefer the slower timing of the other models and keeping the
snow farther west.

Model differences in the QPF amounts, snow amounts, placement are
still a concern Sunday. The NAM/ECMWF favor the northern half of the
forecast area for the higher QPF/snow in the morning, while the
GFS/GEM favor the central/southern sections. Regardless, they do
agree on the location of the surface low center to the MN/SD border
by 18Z. There is also some displacement in the FGEN signal over the
region, but there is plenty of omega moving through the area, along
with upper level divergence. Thaler Q-G divergence points to the
best lift being focused over the southern sections in the morning.
With these differences, have a blend for pops. Forecast soundings
point to all snow.

Differences in the QPF placement and snow amounts continue Sunday
afternoon. The GEM has the most QPF/snow and was discounted. Blended
the GFS/NAM/ECMWF for the coverage of QPF/snow and a more northerly
track. Based on the more northern track, have opted to add
Koochiching, Itasca, northern Cass, northern and central St. Louis,
as well as inland Lake and Cook counties to the winter storm watch.
A disjointed FGEN signal, and best upper level divergence bisecting
the forecast area, points toward the need for a blend of solutions.
Soundings still favor all snow in the afternoon. Some lingering
snow on the backside of the departing surface low over northwest
Wisconsin may provide an additional half inch.

.LONG TERM...(Sunday night through Saturday)
Issued at 251 PM CST Sat Feb 17 2018

A positively tilted trough will dig from the Pacific Northwest late
on Sunday into the Intermountain West by late on Monday. At 850 hPa
a baroclinic zone will setup across the Mid Mississippi River Valley
and extend southwestward to the Central Plains. Along the baroclinic
zone a quasi-stationary front will set up and be the focus for
developing an elongated area low pressure somewhere in the Mid
Mississippi River Valley. This will bring the next round of
precipitation to the Northland. Guidance shows a broad swath of
light precipitation extending northwest of the developing low
beginning early Monday morning continuing through Tuesday, with a
frontogenetical band setting up somewhere in MN/WI. This is due to a
shortwave trough embedded within the longwave trough lifting
through. There is a lot of spread between the GFS/ECMWF/NAM and GEM
guidance in the location and intensity of the precipitation band
that sets up over the CWA, so confidence is low in precipitation and
snow totals at this point. The difference is likely due to
convection developing along where the low pressure system is
developing. Suspect that the latest GEM is the most realistic
solution at this point in time with a tighter precipitation swath,
which would bring less QPF/snow to northern Minnesota. However,
opted to keep a blended solution as guidance is still all over the
place. High temperatures on Monday through Wednesday will generally
be in the teens. Low temperatures will be in the single digits above
and below zero.

Precipitation will come to an end late on Tuesday. High pressure
will build in behind the departing system, shifting flow aloft to a
westerly. This will advect warmer air into the region on Wednesday
and Thursday. Highs on Wednesday and Thursday range from the teens
to the upper 20s. Thursday morning lows will be in the single digits
below zero. The forecast becomes less certain Friday and Saturday as
guidance is all over the place with timing, location and intensity
of the next trough digging in from the Pacific Northwest. The
GEM/ECMWF are currently the slower and drier solution for the
region, while the GFS is faster with more precipitation for the
Northland. Due to the uncertainty stuck with a compromise solution.
This brings chances of snow on Friday/Saturday with highs in the
30s and lows in the teens.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1146 PM CST Sat Feb 17 2018

VFR conditions as of issuance time are expected to continue until
approximately 10z. A potent shortwave and low pressure system
moves across the region beginning around 10z, bringing several
hours of moderate to heavy snow with IFR conditions in
visibilities and ceilings to several terminals, with KDLH and KHIB
the most affected. Sites to the north and south to have a shorter
period of IFR visibilities with MVFR ceilings. Strong winds aloft
will create LLWS for KHYR beginning around 18z, continuing until
00z. A gradual return to VFR is expected to begin around 00z as
the snow band shifts to the southeast, and all but KHYR should be
VFR by the end of the TAF period.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH   5  23   7  17 /  40  90  10  50
INL  -1  15  -8  11 /  20 100   0   0
BRD   7  28   6  16 /  50  70  20  50
HYR   5  33  13  20 /  20  60  30  70
ASX   9  30  13  18 /  20  80  50  70

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...Winter Weather Advisory from 6 AM to 6 PM CST Sunday for MNZ010-
     011-018-025-026-035-037.

     Winter Storm Warning from 6 AM to 6 PM CST Sunday for MNZ012-
     019>021.

LS...None.
&&

$$

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



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