Area Forecast Discussion
Issued by NWS Marquette, MI

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465
FXUS63 KMQT 260734
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
334 AM EDT MON SEP 26 2016

.SHORT TERM...(This evening through Monday)
Issued at 409 PM EDT SUN SEP 25 2016

12Z raobs/latest wv imagery and RAP analysis show hi amplitude
pattern dominating NAmerica featuring deep upr trofs in the plains
and over the Cndn Maritimes arnd an upr rdg over the Great Lks/NW
Ontario. Potent shrtwv lifting nnewd thru the Plains trof is moving
toward Lk Winnipeg with 12hr h5 hgt falls aprchg 100m. Mstr surge in
the warm conveyor belt ribbon ahead of this feature under h85 sw
winds up to 40 kts/sharp pres gradient btwn attendant sfc lo pres in
nrn Manitoba/attendant cold fnt in the plains and sfc hi pres over
Quebec and New England advected 12Z pwats up to about 1.75 inches
over INL/MPX, 250-300 pct of normal. Showers on the ern flank of
this mstr ribbon are impacting mainly the central zns despite drier,
stable airmass shown on the 12Z GRB/APX raobs closer to the sharp
upr rdg axis that has kept the far ern cwa dry. Dry slotting
following the warm conveyor belt has resulted in a band of partial
clrg fm the MN Arrowhead into far nw WI. Looking farther to the w,
there is a pronounced cool pool and plenty of lo clds over the nrn
Plains spreading into MN under the upr trof/behind cold fnt, with
12Z h85/7 temps at Bismarck, ND, down to 4/-2C. The 12Z h85/925 nw
winds at Bismarck were about 50/45 kts and are aiding the strong
caa.

There are a number of fcst concerns in the short term, mainly pops
and winds that wl accompany the passage of the warm conveyor belt
mstr ribbon/sfc cold fropa.

Late this aftn/tngt...Axis of deep mstr/deep lyr qvector cnvgc under
the warm conveyor belt are fcst to shift w-e acrs the cwa thru this
evng, exiting the far e arnd 06Z. Since the showers unstream have
become less wdsprd, wl fcst no hier than likely pops. Mucapes no
more than about 250 j/kg under this warm conveyor belt wl support no
more than isold TS. Dry slotting in the wake of the warm conveyor
belt/cold fropa wl diminish the pops as early as this evng over the
w and may actually bring some brief clrg as obsvd this aftn right
behind cold fropa over MN. But then more backwash mstr/lo clds wl
surge into the area later tngt in the strengthening cyc w flow
behind the fropa. The most wdsprd lo clds and some showers wl impact
mainly the hier terrain of the w with arrival of sharper trof
axis/some upslope wind component. h85 temps falling to about 4C wl
add a lk effect component to the pcpn as well.

Mon...Sharp, slowly veering wsw to wnw cyc flow under slow moving
trof axis/area of deep lyr qvector cnvgc associated with closed lo
driftng thru Ontario just n of Lk Sup wl bring nmrs/even wdsprd lk
enhanced showers to mainly the nw half of the cwa. Although no sharp
pres rise center that would aid an isallobaric component to the wind
is fcst to follow the trof axis, h925 winds up to 40 kts under the
thermal troffing wl support wind gusts aprchg advy criteria at
exposed locations over the Keweenaw Peninsula by later in the aftn.
As the winds veer a bit more toward the w over the ern cwa, waves
are fcst to build sufficiently to cause a hi swim risk in the
beaches of Alger County late in the day. Fortunately, the wx
conditions wl likely discourage swimmers.

.LONG TERM...(Tuesday through Sunday)
Issued at 333 AM EDT MON SEP 26 2016

Focus for this week is on deep upper low and wrapped up sfc low
meandering over the Upper Great Lakes on Tue/Tue night. Ample deep
moisture to h7 and cyclonic flow with lake-h85 delta t/s over 8c
support widespread showers across Upper Michigan. WNW low-level
winds favor higher terrain of western Upper Michigan for the most
rain but it will be windy and damp across the entire cwa.

As upper low center slides across eastern Lk Superior on Tue aftn
and Tue evening and forecasted instability increases /sfc based CAPE
values 400-800j/kg/ could be setting stage for some thunderstorms
and possible waterspout development over scntrl and southeast Lk
Superior. Sfc low in vcnty only boosts low-level convergence which
would provide focus for waterspouts. Delta t/s 6-7c only marginal
for waterspouts per Szilagyi nomagram but convective cloud depth
forecasted up to 23-25 kft could tip the scales. See no reason to
not introduce at least a slight chance of waterspouts Tue aftn into
Tue evening for southern portions of Lk Superior. Locations along
LkSuperior shoreline from Big Bay to Marquette to Grand Marais and
Whitefish Point would be most favored to see waterspouts.

Sfc low sliding by just south of Upper Michigan on Tue night brings
winds around to a more NE direction. Focus for lake enhanced rain
showers should set up mainly west and north central cwa. Rain over
the east may tend to diminishing with downsloping/subsident flow
developing. System should slowly move toward Ohio Valley Wed into
Wed night as strong upper jet plowing across western Canada helps to
push ridge across the northern Plains to northern Ontario and Upper
Great Lakes. Northerly cyclonic flow on northwest flank of exiting
sfc low and lingering moisture blo h7 along with h85 temps 4-5c
should keep some showers going Wed as a weak lake enhanced setup
persists. Coverage and intensity will diminish though as drying
works in from the north as inversion steadily lowers. Waterspout
risk shifts to northern Lk Michigan on Thu as the upper low slides
across. Potential for waterspouts on Wed on northern Lk Michigan may
be even greater than on Lk Superior the previous day as delta t/s
with warmer water temps are 15-16c instead of less than 10c on Lk
Superior. Since upper ridge does not arrive in full force until Thu
there could be a few showers or at least mostly cloudy skies even as
late as Wed night into Thu morning.

Eventually ridging aloft and at the sfc should move in later Thu
into Fri bringing dry weather and a warming trend. ECMWF and to a
certain degree the GEM try to bring the upper low far enough north
by the weekend to bring rain chances back to the Upper Great Lakes.
ECMWF trended this way with 00z run last night and 12z run continued
to show that as well. Latest 00z run from tonight still on board
with that idea and even has qpf across Upper Michigan late Fri. GFS
keeps the upper low too far east of Upper Lakes to bring any precip
to the area. WPC hand drawn progs favor the farther east solution as
well. Will keep riding with the consensus of all guidance which
keeps it dry for Fri into the weekend. Next chance of rain comes
back into the area early next week. Highs Fri into the weekend
should top out in the 60s. Late this week if the high becomes
centered overhead for a night could see mins dip into the upper
30s at typical inland cold spots.
&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 103 AM EDT MON SEP 26 2016

With low-level moisture already back on the increase over western
Upper MI, lower end MVFR conditions will likely prevail thru the
fcst period at KIWD/KCMX as sfc low pres drifts se toward Lake
Superior. Expect an increase in -shra coverage as well with deep
cyclonic flow and cooling air mass introducing a lake enhanced
component to the shra. At KSAW, some drying following recent cold
fropa combined with a downslope component to the wind should allow
VFR conditions to prevail into the morning hrs. MVFR conditions
should redevelop by early aftn and then persist thru the evening.
Winds will also become increasingly gusty today with the strongest
winds at more exposed KCMX where gusts will reach up to around 35kt
in the aftn/evening.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 409 PM EDT SUN SEP 25 2016

Sse winds that will gale force over portions of the e half of the
lake will diminish w to e this evening/tonight along with an
approaching cold front/weakening gradient. Maintained going gale
warning into late tonight for the far e section of the lake as
terrain enhancement may focus stronger winds in this area. A more
widespread w gale to 35-40 kts will develop over Lake Superior on
Mon under the tightening pres gradient/increasing instability behind
a lo pres trof passage. Opted to upgrade the gale watch to a warning
for this event.  With the slow approach of hi pres, these strong
winds will diminish later Tue into Wed. This hi pres will then bring
light winds to end the week.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
  Gale Warning until 4 AM EDT early this morning for LSZ267.

  Gale Warning from 2 PM this afternoon to 5 AM EDT Tuesday for
     LSZ243-244-264>266.

  Gale Warning from 8 AM EDT /7 AM CDT/ this morning to 11 AM EDT
     /10 AM CDT/ Tuesday for LSZ162-263.

  Gale Warning from 11 AM EDT /10 AM CDT/ this morning to 8 AM EDT
     /7 AM CDT/ Tuesday for LSZ240>242.

Lake Michigan...
None.
&&

$$

SHORT TERM...KC
LONG TERM...JLA
AVIATION...Rolfson
MARINE...KC



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