Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 261958

Area Forecast Discussion
National Weather Service Marquette MI
358 PM EDT MON SEP 26 2016

.SHORT TERM...(This evening through Tuesday)
Issued at 357 PM EDT MON SEP 26 2016

12Z raobs/latest wv imagery and RAP analysis show deep upr troffing
dvlpg over the wrn Great Lks as vigorous shrtwv/closed upr lo that
caused 00-12Z h5 hgt falls up to 220m at GRB digs into the area.
Sharp pres gradient on the srn flank of 996mb sfc lo pres over
Ontario has caused some gusty w winds up to 40-45 mph over the more
exposed wrn cwa, in line with obsvd 12z 3k agl nw wind up to 45 kts
at INL. The 12Z INL raob also shows some deep mstr/nearly moist
adiabatic lapse rates up to about 400mb, and this moist airmass in
concert with the sharp cyc llvl flow and h85 temps falling as lo as
2-3C under the thermal trof on the sw flank of the Ontario lo have
resulted in some nmrs lk enhanced showers over mainly the wrn cwa,
where the llvl winds are presenting a sharp upslope component.
Downsloping nature of the wsw winds farther to the e and deep lyr
qvector dvgc/mid lvl drying have limited the shower coverage to
isold-sct away fm this area.

Main fcst concerns in the short term wl focus on pops/winds
associated with closed lo that is fcst to slide slowly se and to
over ecentral Lk Sup on Tue. The arrival of weakening winds/more
mstr and more unstable lapse rates over the e half of Lk Sup could
result in some waterspouts there late tngt into Tue.

Tngt...As closed lo shifts slowly to the sse and to over far nrn Lk
Sup by 12Z Tue, deeper mstr/qvector cnvgc are fcst to overspread the
entire cwa. Although the more wdsprd lk enhanced showers wl persist
over the wrn cwa with continued sharper upslope winds, the arrival
of some dynamic support and deeper mstr within the llvl cyc flow wl
increase shower coverage over the rest of the cwa. But downsloping
flow wl limit the pops over the se portion of the cwa. Winds thru
this evng wl remain quite gusty over the w under lingering tight
pres gradient/h925 w winds up to 40kts, but the closer aprch of the
sfc lo pres/weakening pres gradient wl cause the winds to diminish
later. Fcst mucapes as hi as 500-750j/kg within a deep convective
lyr featuring narrow, skinny cape and the weakening winds/deep,
sharp cyc flow may allow for a few TS/waterspouts over the e half of
Lk Sup. Since the llvl winds are fcst to remain more wsw near the
lkshore over the e half of the cwa, any deeper convection/
waterspouts wl remain offshore of the e half of Upr MI.

Tue...The closed lo is progged to drift slowly s to to over scentral
Lk Sup by late in the day. Although wind speeds wl diminish under
the grdly flattening pres gradient, lingering deep mstr/cyc flow/
some deep lyr qvector cnvgc wl support continued showers, which wl
be most nmrs-wdsprd over the hier terrain of the nw half with an
upslope flow. Although a downslope flow wl limit pops over the se
half, the closer aprch of the closed lo wl support at least sct
showers there. Since the area of modest mucape up to 500-750 j/kg wl
tend to slide to the ssw with the upr lo track, the threat of TS, as
well as some waterspouts under the weaker winds under the flatter
pres gradient closer to the lo center, wl migrate toward the
nearshore areas fm the Keweenaw e to Whitefish Pt by later in the

.LONG TERM...(Tuesday night through Monday)
Issued at 337 PM EDT MON SEP 26 2016

Attention remains focused on the first day or two of the long term
as the closed low shifts out of the area.

Models indicate that the low will be over south central Lake
Superior at 00Z Wed, which is a westward shift from previous runs.
This trend may slightly continue, but would think that models will
have a pretty good handle on the system at this point. The low will
shift to northern Lake Michigan by 06Z Wed, southern Lake Michigan
by 12Z Wed, then gradually shift to central or eastern KY by Thu

As the low shifts through and out of the area, the main hazards will
be gusty winds, high waves/beach erosion, and waterspout potential.
NE winds gusting to 30-35mph will gradually diminish over and near
Lake Superior Tue night into Wed, but winds will increase to 25-
30mph over and along northern Lake Michigan on Wed into Wed evening.
Winds will drive waves up to around 8` over western Lake Superior,
which may result in some minor beach erosion. As for waterspouts,
favored areas will be south central Lake Superior Tue evening and
Tue night then over northern Lake Michigan late Tue night into Wed.

Rain showers will be most focused over north central and western
Upper MI Tue night, transitioning to northern Lake Michigan Wed into
Wed evening as ridging moves in from the NW.

Challenge late in the week is how close does the upper low come to
the area as it moves back to the N from KY. The ECMWF bring it
across central Lower MI and Lake Huron this weekend into early next
week, while the GFS takes it across OH and Lake Erie. The ECMWF
solution brings chances for rain showers Fri through the weekend,
while the GFS confines any precip chances to the far eastern CWA.
With low confidence in the track of the low, stuck with the
consensus blend late week through day 7.

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 142 PM EDT MON SEP 26 2016

A moist cyc upslope wnw flow wl bring predominant lo end MVFR
conditions to CMX/IWD this fcst period. IFR conditions are possible
at times, especially at IWD late as the flow veers more to the NW
and increases the overwater trajectory of the air into that site.
The downslope nature of the flow wl allow for hier end MVFR cigs to
prevail at SAW, but even there the cig is likely to drop into the
lower MVFR range by the early mrng hrs on Tue as lo pres now in
Ontario sinks into Lk Sup and draws closer. Gusty winds will also
continue thru this evng, especially at the more exposed CMX location,
where gusts aoa 35 kts are likely. The strongest winds will tend to
diminish later tngt into Tue with the closer approach of the Ontario
lo pres and a weakening pres gradient.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 357 PM EDT MON SEP 26 2016

As a lo pres over Ontario sinks slowly s and over Lake Superior, the
pres gradient over the waters will flatten and cause ongoing w gales
to diminish under 30 kts by mid morning on Tue. There could be some
waterspouts over the e half of Lake Superior late tonight into Tue
night under the slowly passing lo pres. With the slow approach of
trailing hi pres, the winds will continue to slowly diminish later
Tue into Wed. This hi pres will then bring lighter e to ne winds
under 20 kts to end the week.

Upper Michigan...
Lake Superior...
  Gale Warning until 5 AM EDT Tuesday for LSZ243-244-264>266.

  Gale Warning until 11 AM EDT /10 AM CDT/ Tuesday for LSZ162-263.

  Gale Warning until 8 AM EDT /7 AM CDT/ Tuesday for LSZ240>242.

Lake Michigan...


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