Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 272335

Area Forecast Discussion
National Weather Service Marquette MI
735 PM EDT Tue Sep 27 2016

.SHORT TERM...(This evening through Wednesday)
Issued at 352 PM EDT TUE SEP 27 2016

12Z raobs/latest wv imagery and RAP analysis show a closed upr lo
dropping slowly swd acrs Lk Sup. Deep cyc, cool flow arnd this
disturbance in concert with deep mstr depicted on the 12Z INL raob
and some dynamic forcing are generating some showers over the cwa
this aftn. With the cld cover and h85 temps arnd 4C /Lk Sup temps
range fm about 10-15C/, there is some lk enhancement to the pcpn
as temps are holding in the upr 40s to mid 50s. There is some drying
evident wrapping arnd the closed lo associated with large scale
subsidence/deep lyr qvector dvgc on the nrn flank of that feature
that is tending to diminish the shower coverage over much of Lk Sup
and the nrn land cwa.

Tngt...Closed lo fcst over scentral Lk Sup early this evng is
progged to sink steadily swd to over scentral Lk MI by 12Z Wed, with
large scale subsidence/deep lyr qvector dvgc/mid lvl drying
overspreading Upr MI fm the n. With these trends in mind, expect the
showers to become more sct by later tngt. Although the h85-lk
temp difference wl be marginal for lk effect pcpn, lingering llvl
mstr and the sharp cyc flow should still support some showers. Since
winds wl also shift steadily to a more cyc ne direction during
the ngt with the passage of the sfc lo to the s of the cwa, expect
the lk effect showers to become most nmrs over the w and ncntrl cwa,
where this ne flow wl upslope. There could still be some waterspouts
late this aftn into the evng hrs over mainly the scentral portion
of the lk to the Keweenaw under lingering deeper mstr/area of lighter
winds near the sfc lo center and where the hier res models indicate
mucapes as hi as 500-750j/kg over the somewhat warmer nearshore
waters. But rising hgts/mid lvl drying and lowering mucape/hier winds
on the nrn flank of departing sfc lo wl diminish this threat after
the evng. The arrival of the ligher winds closer to the track of the
sfc lo wl also bring the threat of waterspouts to the Lk MI
nearshore waters tngt.

Wed...With continued hgt rises/mid lvl drying/lowering subsidence
invrn/slowly weakening cyc nne flow to the n of the closed lo
sinking into the Lower Lks, the shower coverage wl diminish. The
best chc for more persistent showers wl be over the hier terrain
of the w and ncentral cwa impacted by upsloping and over the far
se on the nw edge of some lingering deeper mstr closer to the
departing closed lo to the sse. Even though the shower coverage wl
diminish, fcst llvl mstr/sfc obs upstream sug a good deal of lo clds
wl linger and limit diurnal temp recovery.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 332 PM EDT TUE SEP 27 2016

High pressure building in from the northwest Wed night and Thu
should end showers and allow for decreasing clouds. The NAM and GFS
soundings indicate that there could be some near sfc moisture
trapped beneath strengthening subsidence inversion Wed night into
early Thu which could maybe lead to some stratus formation for
locations favored by upslope ne flow. Models indicate there should
be enough wind/mixing to preclude fog formation so removed patchy
fog for western counties Wed night into early Thu. Cut-off mid-upper
level low pressure system remaining nearly stationary over the TN
River Valley should maintain dry conditions through Fri. Expect mins
Wed night and Thu night to range from lower 40s interior west to mid
50s near Lake Superior in onshore ne flow. H85 temps of 7-8C should
support inland max temps mainly in the mid to upper 60s on Thu and
H85 temps of 8-10c should support inland max temps in the upper 60s
to lower 70 on Fri. Continued onshore ne flow will keep max temps
cooler both days near Lake Superior in the lower to mid 60s. Influx
of mid-Atlantic moisture wrapping around cut-off low could lead to
increase in mid-level clouds on Fri over the southeast half of U.P.

Models in general agreement with mid-upper low moving slowly
northward into the Ohio Valley/Great Lakes region Fri night into the
weekend and getting eventually caught back in westerly mid-latitude
flow in response to deepening mid-upper trough over the West Coast.
Continued influx of deeper mid-Atlantic moisture wrapping around low
and increasingly cyclonic ne flow will lead to increased chances for
rain beginning Fri night and continuing into the weekend especially
for the east half of Upper Mi closer to the movement of mid-upper

Model trends indicate closed low slowly moving east toward New
England Sun night into Mon as western CONUS trough moves slowly
eastward. Should see improving weather across Upper Michigan Sun
night into Mon as upper level ridging from west becomes main feature
again. Expect increasing clouds from the west late Mon night into
Tuesday as mid-level moisture increases with approach of mid-upper
trough from western CONUS and associated sfc trough from the Plains.
Some increase in mid-level q-vector convergence ahead of the trough
could also bring some light rain into west and central Upper Mi on
Tue. Not surprisingly the 12z GFS is showing its typical bias with a
quicker advance of trough than the 12z ECMWF so will include some low
chance pops for rain over west and central counties mainly Tue

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 735 PM EDT TUE SEP 27 2016

A low pressure system centered over central Lake Superior will
continue to slowly drift to the south across the western Great Lakes
region overnight. This feature will produce IFR and low end MVFR
conditions at all three TAF sites overnight. IFR conditions favored
at KIWD due to persistent moist upslope flow off the lake. KSAW will
also see upslope flow developing and should see ceilings drop to IFR
for a time after 8Z. With winds expected to pick up at KCMX, enough
mixing to occur to keep cigs at MVFR but cannot rule out a brief
period of IFR there. KSAW may see a brief moment of VFR early in the
forecast as the low passes overhead but will quickly return to MVFR
and possibly IFR. As the low continues to drop south on Wednesday,
drier air will start infiltrating into the region and will bring
about slightly improving conditions at KIWD and KSAW with KCMX
becoming VFR by the afternoon.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 332 PM EDT TUE SEP 27 2016

As low pressure over eastern Lake Superior weakens and sinks slowly
south of the area through Wednesday, the pressure gradient over the
lake will gradually slacken causing north-northeast winds to 30
knots tonight over west and north central Lake Superior to diminish
to 20 to 25 knots on Wed. There could be some gale gusts to 35 knots
tonight mainly over the western half of Lake Superior. With the slow
approach of trailing high pressure, the winds will continue to
diminish late Wed into the weekend with lighter east to northeast
winds under 20 kts expected.

Upper Michigan...
Lake Superior...
Lake Michigan...


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