Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 202049

Area Forecast Discussion
National Weather Service Marquette MI
449 PM EDT SAT AUG 20 2016

.SHORT TERM...(This evening through Sunday)
Issued at 449 PM EDT SAT AUG 20 2016

Fall-like system is moving into the western Great Lakes this aftn as
water vapor imagery and RAP analysis show a well-defined shortwave
over the Upper Mississippi Valley. Mcv tracking ne across northern
Lake MI has resulted in the associated sfc low pres being ill-
defined. The main synoptic low pres is in far ne WI while mcv
generated sfc low is just s of Manistique. Vigorous deep layer
forcing ahead of the shortwave has produced widespread rainfall
across the fcst area today. Thunder has brushed se Delta and
southern Schoolcraft counties.

Main fcst issues during the short term involve pcpn trends and
potential of headline worthy strong winds. Deepening shortwave trof
will move over the Upper Great Lakes tonight with 12hr 500mb height
falls up to 120m. At the sfc, associated deepening sfc low will
track ne across eastern Upper MI and out over eastern Lake Superior.
Even at this short of a time range, models still show some small,
but important differences on sfc low track/speed/strength, but are
converging. Hourly RAP/HRRR runs today have remained quicker/farther
e, lifting the low out over Lake Superior this evening, btwn Grand
Marais and Whitefish Pt, then exting the lake by 06z, diminishing
the risk of advy level winds for the land portion of the fcst area.
NAM, including the high res NAM window, and the GEM which have been
deepest/slowest/farthest w are shifting e, but are still on the
slower side. NAM/GEM solutions had posed a much greater potential of
stronger winds affecting more of Lake Superior and adjacent portions
of Upper MI. Since colder air is not rushing into the backside of
the low pres quick enough to really increase overwater instability
and thus strengthen/slow system as normally occurs with systems
during the fall, will lean away from the slower/strongest wind
solutions. That said, solid gales will develop on roughly the e half
of Lake Superior tonight with warm lake waters and caa leading to
more efficient mixing of 40+kt winds down toward the sfc.
Since caa is not especially strong and since isallobaric component
is weak, don`t think stronger winds over the lake will be realized
inland. For a brief time, some lakeshore locations may see some
gusts to 45mph (around Copper Harbor and east of Marquette). The
strongest winds out e will occur late tonight/early Sun morning.
With limited coverage/duration, wind advy does not appear warranted.
Evening shift can reassess situation.

As for pcpn, deep layer q-vector divergence and some mid level
drying pushing across the s central and eastern fcst area will lead
to nothing more than isold/sct shra this evening. Farther n and w,
with lingering deep layer forcing, deep cyclonic flow and incoming
air mass cool enough to support lake enhancement, expect more
persistent shra across w and n central Upper MI. May start to see
some diminishing of pcpn over the w late.

On Sun, lake enhanced shra will diminish/end from w to e, though
shra may linger thru the aftn over the far e. In addition, moisture
from the lake/850mb thermal trof and daytime heating may result in a
few sprinkles/-shra developing/lingering into the early aftn over
the s central fcst area. Abundant cloud cover in the morning will
gradually give way to increasing sunshine, mainly over western Upper
MI as flow becomes more anticylconic and 850mb temps begin to
moderate. High temps Sun will be in the 60s, but may still top 70F
over the far s central. For those looking for relief from the high
dwpts that have mostly dominated over the last couple of weeks,
dwpts on Sun will fall back into the 40s and lower 50s. While Sun
will be cool/cloudy and at least wet during the morning hrs, there
will be a high swim risk for the Lake Superior beaches of Marquette
and Alger counties.

.LONG TERM...(Sunday night through Saturday)
Issued at 356 PM EDT SAT AUG 20 2016

Sunday Night: Expect a more settled pattern as we start next week as
WNW flow takes hold across the north-central CONUS. Better moisture
will depart and the pressure gradient will lax heading into Sunday
night, allowing for a good radiational cooling set-up across much of
the CWA. Other than a few lingering light showers or strato-cumulus
across the NE in the evening, expect mostly clear skies through the
night. Continued to favor the lower end of guidance for min temps,
with low 40s expected across portions of the interior.

Monday and Tuesday: Increasing WAA on Monday will support isolated
showers/storms to the north of the CWA. Capping will prevent precip
initiation away from Lake Superior and possibly the Keweenaw
Peninsula during the day. However, the nose of a strengthening LLJ
ahead of an approaching sfc low over the northern Plains may induce
some elevated convection Monday night. Dry and warm conditions are
then expected for Sunday, with highs pushing well into the 80s
amidst gusty SW winds.

Wednesday through Saturday: Phasing of a cluster of troughs will
occur across the region Wednesday into Thursday while the a pair of
upper jet axes cross the area. Forcing becomes a bit muddled given
the interactions between all of these synoptic features, but best
chances for showers and possibly some thunderstorms will be Wednesday
afternoon as a sfc trough traverses the CWA. With several convective
parameters far from ideal Wednesday afternoon, no strong to severe
storms are expected at this time.

Surface high pressure and upper ridging will then bring dry and
mostly clear conditions Friday into early Saturday before a rather
open mid-level wave induces mainly showers to close out the weekend.

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 136 PM EDT SAT AUG 20 2016

With deepening low pres over ne WI crossing eastern Lake Superior
tonight, shra will continue. To the w of the low track, upslope
winds off Lake Superior should result in prevailing LIFR conditions
at KSAW into the evening hrs. KCMX should drop to IFR in the next
few hrs, but confidence is not especially high as northerly winds
will not be the ideal upslope direction for that terminal. KIWD
should see prevailing IFR conditions under a better upslope wind
direction. Overnight into Sun morning, expect gradual improvement
from w to e. KIWD/KCMX should break out to VFR around 12Z. At KSAW,
expect MVFR conditions to develop late tonight, but VFR may not
develop until near or just beyond this fcst period. Finally, closer
to the low pres track, gusty winds will impact KCMX/KSAW for much of
this fcst period with gusts as high as 30kt at times tonight.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 449 PM EDT SAT AUG 20 2016

With a preview of the upcoming fall season, a deepening sfc low pres
will track ne across far eastern Lake Superior this evening and then
across Ontario into Quebec overnight and Sun morning. N to nw gales
of 35-45kt will develop this evening over roughly the e half of Lake
Superior. Not out of the question that a few storm force gusts could
occur e of Stannard Rock, especially toward Caribou Island/Grand
Marais/Whitefish Pt late tonight/early Sun morning. As the low
departs the area, winds will diminish blo gale force by early Sun
aftn. Winds will gradually diminish further to under 20kt from w to
e Sun aftn and night as high pres ridge arrives. As the high
departs, winds will become s to sw on Mon, but should remain under
20kt. Then, tightening pres gradient in response to the next low
pres trof moving out over the Plains will result in increasing
winds, with gusts possibly into the 20-25kt range at times Mon night
thru Wed, and even into Thu after the trof passes.

Upper Michigan...
  Beach Hazards Statement until 10 PM EDT this evening for MIZ005-

Lake Superior...
  Gale Warning from 3 AM to 2 PM EDT Sunday for LSZ251-267.

  Gale Warning from 8 PM this evening to 2 PM EDT Sunday for

  Gale Warning from 8 PM this evening to 8 AM EDT Sunday for

  Gale Warning from 2 AM to noon EDT Sunday for LSZ250.

Lake Michigan...
  Gale Warning from 11 PM this evening to 11 AM EDT Sunday for



SHORT TERM...Rolfson
LONG TERM...Kluber
MARINE...Rolfson is the U.S. government's official web portal to all federal, state and local government web resources and services.