Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 181222 AAA

Area Forecast Discussion...UPDATED
National Weather Service Duluth MN
722 AM CDT Fri Aug 18 2017

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

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 12Z TAFS through 12Z Saturday morning)
Issued at 721 AM CDT Fri Aug 18 2017

MVFR/IFR/LIFR conditions will gradually improve to VFR later this
morning. An area of low pressure will advance generally eastward
across central Minnesota with high overcast expected across the
area above the lower ceilings. A few rain showers are possible and
a rumble or two of thunder isn`t out of the question either.
Included VCTS at HIB, BRD, and INL this afternoon, where the best
chance of storms will be found. Skies will gradually clear tonight
which should allow for radational cooling and fog formation. Have
some lower visibility with fog at HIB, INL, BRD, and HYR. Not as
confident at DLH where high clouds may limit fog potential.


DLH  76  55  80  60 /  20  20   0  20
INL  77  51  81  60 /  30  10   0  30
BRD  73  54  81  61 /  40  10   0  20
HYR  75  53  81  58 /  20  20  10  10
ASX  76  57  84  61 /  10  10   0  10




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