Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 122045

Area Forecast Discussion
National Weather Service Duluth MN
345 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 18Z TAFS through 18Z Sunday afternoon)
Issued at 1253 PM CDT Sat Aug 12 2017

VFR conditions are expected through this forecast period. High
pressure over the region will result in relatively light winds
today and tonight. An area of low pressure aloft will move across
central and southern Minnesota tonight and Sunday, which should
result in increasing cloud cover and a chance of rain showers
Sunday morning. Have included a mention of VCSH at BRD, where
the best chance of showers is forecast as of this update. With
cloud cover increasing overnight, think the potential for fog is
low and have kept a slight visibility reduction at HIB from
previous forecast.


DLH  53  74  54  70 /   0  30  40  30
INL  48  77  51  77 /   0  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




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