Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 181059

Area Forecast Discussion
National Weather Service Marquette MI
659 AM EDT Fri Aug 18 2017

.SHORT TERM...(Today and tonight)
Issued at 359 AM EDT FRI AUG 18 2017

Water vapor imagery shows troughing across the Upper Great Lakes
region this morning with the associated surface low tracking across
eastern Lake Superior. Upstream of the area, additional shortwave
activity is also apparent as it digs across the northern and central
Plains. A few lingering showers continued to impact portions of
Upper Michigan both ahead of and behind the main surface low. A few
areas of fog were observed across the area, primarily across the
Keweenaw Peninsula where upslope flow is most prevalent.

Today, as the above mentioned low pressure system continues to lift
northeast out of the area, cold air advection and lingering cloud
cover will help keep temperatures about 10 degrees below normal for
this time of year. Some locations, especially those downwind of Lake
Superior across the north central and eastern portions of Upper
Michigan will struggle to climb into the mid 60s. In fact, some
locations may see high temperatures occur this morning, with a
cooling trend through the afternoon. Given the track of the system,
it looks like we will see more northwesterly than northerly winds on
the back side of the system. Given this flow orientation with the
terrain, this should limit the temporal extent of any lingering
drizzle chances across the north central portions of the area to at
least the morning hours. Across the Keweenaw where upslope flow will
be better oriented with the terrain, expect the fog to linger across
the higher terrain this morning and possibly into the early
afternoon hours. Further east, wrap around showers will linger
through a good portion of the day. Not expecting widespread showers,
but a few locations may pick up a tenth to a quarter of an inch of
additional rainfall. As the pressure gradient and pressure rises
behind the exiting system linger across the region, expect winds to
be rather gusty today. These gusty winds will be strongest near the
shores of Lake Superior and will create a high swim risk for
Marquette and Alger counties.

Late this afternoon through the overnight hours, as the upstream
shortwave activity previously mentioned begins to dig across the
Upper Great Lakes region, it isn`t out of the question that we could
see scattered showers track southeast across the area.

.LONG TERM...(Saturday through Thursday)
Issued at 457 AM EDT FRI AUG 18 2017

Models suggest that a slowly progressive pattern will prevail into
next week with a transition to zonal flow this weekend and to a more
amplified pattern as a trough over Alaska drifts through the Gulf
of Alaska to BC/Alberta late next week. The resulting downstream
ridge/trough will bring mainly nw flow through the wrn Great Lakes
from Tue night into Friday. Above normal temps this weekend into
Monday will give way to seasonably cool conditions from Tuesday
through the rest of the week.

Saturday, even with drier air over the region, dewpoints into the
mid and upper 50s with daytime heating pushing inland temps into the
upper 70s will result in MLCAPE values to around 500 J/Kg. Lake
breeze boundaries over the ern cwa should be able to trigger isold
showers over mainly s cntrl locations by mid afternoon.

Sunday, increasing srly flow WAA ahead of a front edging into the
region will help boost temps into the lower to mid 80s. Although
MLCAPE values may climb to around 2k J/Kg, capping will be strong
enough to limit convection potential, so that only lower end POPS
with isold/sct shra/tsra are expected over mainly the north from the
late afternoon into the evening that may be supported by any weak
shortwave trough that moves through in the zonal pattern.

Monday, the combination of a frontal boundary developing over the
area combined with the likelihood of a stronger shortwave emerging
from the nrn plains will bring greater shra/tsra chances over the
area. However, confidence with any timing is low given model

Expect drier conditions again by Tuesday that should persist through
the end of the week as the frontal boundary drops to the south with
the mid level trough developing toward the Great Lakes. As is often
the case with nw flow patterns some mainly diurnal light showers may
be possible with any weak shrtwvs moving through the area.

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 658 AM EDT FRI AUG 18 2017

Low ceilings, and at times lower visibilities, will gradually
improve from west to east across all terminals as low pressure exits
the region. Expect lingering showers to continue to impact all
terminals with a similar decrease in coverage from west to east
through the day. Expect winds to be gusty at times, especially at
KSAW and KCMX. There is a slight chance for a few scattered rain
showers late tonight into early tomorrow morning. Confidence in
development and overall coverage given the nocturnal setting was not
high enough to include mentions within the TAFs at this time.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 359 AM EDT FRI AUG 18 2017

Today, as low pressure continues to lift northeast across eastern
portions of Lake Superior and up into Canada, expect winds behind
the system to be 20-30 knots across the central and eastern portions
of the lake. A few gale force gusts will be possible, especially
closer to the lake shore where winds may become locally enhanced.
Further to the west, winds will begin to relax through the afternoon
to around 10 to 20 knots.

Tonight as the pressure gradient relaxes across the area, expect
winds to decrease to around 10 to 20 knots. Winds are expected to
remain below 20 knots through the weekend and a good portions of
next week.

Upper Michigan...
  Beach Hazards Statement through this evening for MIZ005-006.

Lake Superior...
Lake Michigan...


SHORT TERM...Ritzman
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