Area Forecast Discussion
Issued by NWS Duluth, MN

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000
FXUS63 KDLH 122338
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
638 PM CDT Sat Aug 12 2017

.SHORT TERM...(This evening through Sunday)
Issued at 345 PM CDT Sat Aug 12 2017

High pressure building across the Upper Midwest today is leading to
mainly sunny skies with a widespread cu field across much of the
region. A few showers and storms north of the international
border, with some entering into the MN Arrowhead region as
expected - none strong given the weak instability and light wind
field in place. On the synoptic scale a mid-level shortwave trough
is approaching the northern Plains today, tracking east towards
the Upper Midwest tonight into Sunday. Scattered to widespread
convection has developed across the central and northern high
plains in response to the broad-scale lift within an area of broad
southerly flow. This convection will makes its way east into
western Minnesota late today into tonight, reaching central
Minnesota including the Brainerd Lakes region towards Sunday
morning. While there will be a bit of instability available for
thunderstorms, overall soundings look like just a few rumbles of
thunder in east-central Minnesota with otherwise light/moderate
rain showers. Best precipitation chances will be central to east
central Minnesota as showers slowly track east through the day
Sunday. Otherwise increasing clouds through the day.

Lows tonight in the 40s to 50s, with some inland locations fall as
cool as the low 40s given mainly clear skies overnight. Highs
Sunday in the 60s where rain is expected in central MN due to the
rain/cloud cover, 70s elsewhere where at least partly sunny skies
are expected for much of the day.

.LONG TERM...(Sunday night through Saturday)
Issued at 345 PM CDT Sat Aug 12 2017

Main forecast challenge for the long term involves precipitation
chances and timing for the upcoming week as several periods of
showers and thunderstorms are possible.

Sunday evening opens with the quasi-blocked pattern over the
northern North American continent remaining in place. A shortwave
trough and associated vort max is forecast over the southern half
of Minnesota. Look for skies to remain mostly cloudy over much of
the area with a chance of showers and isolated thunderstorms for
most locales. Highest POPs will remain over the southern half of
the forecast area. The open wave will gradually shift farther
eastward on Monday with rain and thunderstorm chances shifting
east during the day. A few strong storms are possible Monday
afternoon and early Monday evening over northwest Wisconsin with
the vort max over the northern St. Croix River Valley. Should
clouds part, deepening of the boundary layer will boost MLCAPE
values into the 750-1250 J/kg range. Ambient vorticity and low-
level wind shear would be supportive of a few supercells with an
associated risk of large hail. There are many challenges to
overcome in order to generate sufficient instability for strong
storms, including cloud cover and the position of the upper low,
and a potentially stout cap indicated by NAM BUFR profiles around
600 mb.

The trough and associated precipitation will shift east out of
the Northland Monday night. Skies will briefly clear as weak high
pressure builds into the area. The next trough will move into
Minnesota late Monday night. Rain chances gradually increase
Tuesday afternoon with rain becoming likely Tuesday night through
Wednesday night. Strong boundary layer moistening on southerly
low-level winds raises the spectre of excessive rainfall over
portions of the Northland. With the 12Z runs today, the most
favored area seems to be the eastern half of the CWA, including
the Twin Ports, Arrowhead, and northwest Wisconsin. The suite of
ensemble members, means, and deterministic guidance features a
high probability of precipitation of at least our southern
forecast area. Have raised POPs considerably from the consensus
blends between 00Z Wednesday and 06Z Thursday to reflect the high
confidence in measurable rainfall.

The shortwave trough will close off and drift into northwest
Ontario Wednesday night and Thursday keeping partly to mostly
cloudy skies in place, but shower chances diminish. By late next
week the western longwave trough will shift east into the
Canadian Prairies and the Upper Midwest. Another shortwave trough
will rotate through the planetary wave bringing a chance of rain
and thunderstorms back to the Northland Thursday night through
Friday night.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 635 PM CDT Sat Aug 12 2017

High pressure will gradually lose its grip on the Northland
weather over the duration of the TAF period. An area of low
pressure will move out of the Northern Plains late tonight and
especially on Sunday, bringing an area of showers and
thunderstorms into the CWA on Sunday. The best chance of
precipitation will be in the KBRD area, which will be closest to
the low pressure system. The showers/storms will then move toward
the KHIB and KDLH areas during the mid to late afternoon, before
spreading across the KHYR mainly after the TAF period. Some MVFR
or even IFR CIG`s and VSBY`s will be possible in the KBRD area
during the afternoon. Otherwise, it should largely be VFR with
perhaps a bit of fog overnight.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  53  74  54  70 /   0  30  40  30
INL  48  77  51  77 /  20  10  10  10
BRD  54  66  55  72 /  20  70  60  30
HYR  50  75  55  72 /   0  30  60  50
ASX  54  79  56  74 /   0  20  50  50

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...None.
&&

$$

SHORT TERM...JJM
LONG TERM...Huyck
AVIATION...DAP



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