Area Forecast Discussion
Issued by NWS Duluth, MN

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000
FXUS63 KDLH 181735
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1235 PM CDT Fri Aug 18 2017

.UPDATE...
Issued at 1223 PM CDT Fri Aug 18 2017

Update for the 18z Aviation Discussion below.

UPDATE Issued at 721 AM CDT Fri Aug 18 2017

Update for new 12Z Aviation Discussion below.

&&

.SHORT TERM...(Today through Saturday)
Issued at 421 AM CDT Fri Aug 18 2017

A chance for isolated/scattered showers/storms today across
northern Minnesota and parts of northwest Wisconsin under partly
sunny skies today, then warmer and mostly sunny on Saturday.

On the synoptic scale a mid-level shortwave will subtly deepen as
it moves from southern Manitoba southeast across the Upper
Midwest today. With clearing skies today, diurnal heating will
lead to Cu developing across the region today, and with the wave
coming across leading to broad-scale lift (or at least a lack of
strong subsidence) there will be at least isolated showers
developing this afternoon. Instability on the order of around 1000
J/kg SBCAPE may lead to some brief thunderstorms, though weak
winds through the column (nothing stronger than about 25 knots)
will lead to short-duration storms. Otherwise northwest winds
today with highs in the 70s.

Tonight the afternoon Cu clears out and another round of fog is
expected to develop away from Lake Superior. Lows upper 50s to low
60s.

Warmer Saturday as a mid-level ridge building across the Great
Plains leads to broad-scale subsidence, though scattered diurnally
driven afternoon "fair weather" Cu expected. Highs around 80.

.LONG TERM...(Saturday night through Thursday)
Issued at 421 AM CDT Fri Aug 18 2017

Main concerns for the long-term involve cloud cover and
precipitation chances Sunday evening through Tuesday morning.

Surface high pressure is forecast over the Midwest Saturday
evening as the mid-level pattern transitions to quasi-zonal flow.
Surface low pressure over northern Manitoba will advance eastward
ahead of a shortwave trough over the western Canadian Prairies. A
cool front will trail south into the Northern Plains and Upper
Midwest and move eastward as well. Convergence along the frontal
boundary may be sufficient to generate a few showers or
thunderstorms Saturday night and Sunday morning. Held onto mainly
slight chance POPs, with a few pockets of low-end chance POPs.
There are several differences between deterministic models with
the 00Z packages, and confidence is not especially high in any
particular location receiving rain. The frontal boundary will
stall out to our south and eventually move northward as a warm
front Sunday night and Monday.

A southern stream shortwave trough will move through the Four
Corners region and into the western Plains with lee cyclogenesis
over southeast Colorado Sunday and Sunday night. The low pressure
at the surface and aloft will bring clouds and rain showers north
into the region. There are some convective elements in the GFS and
NAM solutions which result in lower confidence. There is a
potential for an MCS to develop Sunday afternoon/evening in
Nebraska or South Dakota, which would then ride east near the warm
front and into Minnesota and eventually Wisconsin. Considering
the difficulty in resolving storm-scale features 3.5 days before
the event support sticking with a consensus approach to POPs and
precip at this time. Have lowered max temps a few degrees below
the consensus blends Monday as a 3-hour window of the upcoming
solar eclipse will have its greatest affects during peak heating.
Further nudges cooler may be needed with the next several forecast
cycles. Several deterministic models point to a potential for
brief clearing during the early afternoon Monday, which would
permit viewing some of the eclipse for portions of the Northland.

A progressive northern stream shortwave trough will move through
the northern Rockies and into region Monday night. Rain chances
increase once again Monday night and Tuesday morning as that
trough moves through. For the remainder of the week, an omega
blocking pattern evolves with anchoring low pressure over eastern
and western Canada and a high amplitude ridge over the center of
the continent. The Northland will be on the edge of the
northwesterly flow aloft and the ridge to the west. Precipitation
chances will be low and temperatures will trend near normal.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1235 PM CDT Fri Aug 18 2017

VFR conditions to continue for this afternoon through the evening
over all of the Northland TAF sites. High-level cirrus, with
possibly some lower cumulus clouds, should continue through the
afternoon as modest showers and storms have formed to the south
and west this morning/afternoon. A mid-level shortwave will
support at least chances of showers and thunderstorms, from KBRD
northeastward towards KINL and over the Iron Range of Minnesota.
The high-resolution models differ on the areal coverage of this
activity, so confidence is a bit low on impacts to TAF sites.
Still, continued the mention of VCSH/VCTS across most of the
sites.

A ridge of high pressure then moves into the region tonight,
leading to clearing skies over the Northland. This, coupled with
light winds, will lead to the development of MVFR/IFR fog
for all of the TAF sites, except for KDLH.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  75  55  80  60 /  20  20   0  20
INL  76  51  81  60 /  40  10   0  30
BRD  73  54  81  61 /  40  20   0  20
HYR  74  53  81  58 /  20  20   0  10
ASX  75  57  84  61 /  10  20   0  10

&&

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

$$

UPDATE...JTS
SHORT TERM...JJM
LONG TERM...Huyck
AVIATION...JTS



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