Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 210554

Area Forecast Discussion
National Weather Service Marquette MI
154 AM EDT WED SEP 21 2016

.SHORT TERM...(This evening through Wednesday)
Issued at 414 PM EDT TUE SEP 20 2016

WV imagery and RAP analysis indicated a zonal pattern across most of
the nrn CONUS with a trough moving into the Pacific Northwest. A
weak shortwave trough and area of 800-600 mb fgen supported some
light showers or sprinkles from near KDLH into wrn Upper Michigan.
Very dry air below 700 mb will limit the extent of the pcpn with only
slight chance pops mentioned late this afternoon. Otherwise, mid
clouds were thickening over the area with a broad area of 300-310k
isentropic lift in advance of sfc low pres over South Dakota.

Tonight, expect mid clouds to linger over the region in the waa
pattern with the 850-700 baroclinic zone lingering over the area.
Shra/tsra are expected to remain south of the cwa, closer to the
850mb front and higher MUCAPE values. Otherwise, the clouds will
keep min temps mainly in the 50s.

Wednesday, pcpn chances will increase from s to n as the 850 mb
front gradually lifts to the north. Additional weak shortwaves in
the fast zonal pattern will likely also support shra/tsra
development. However, with the relatively dry low level ne flow
north of the front, the pcpn into the nrn cwa will be slow with
likely pops south and only chance pops north. With MUCAPE values
fcst into the 500-1000 J/Kg over the far south some TS will also be
possible. The thickening clouds will limit highs to the upper 60s to
lower 70s.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 311 PM EDT TUE SEP 20 2016

Still on track to see zonal flow aloft mid week transitioning to
more amplified flow by this weekend as sharp ridge develops over the
central Conus between upper trough over eastern Canada and trough
crossing western Conus. At the sfc, a stationary front will lift
across the Upper Great Lakes Wed night through Thu Night, then
slowly settle south on Fri. Waves of low pressure tracking along
the front will help enhance rain chances. Models have been locked on
to overall scenario with pwats upward of 1.25 inches lifting into
the stationary front and along/ahead of the waves of low pressure
and large scale lift over entire area enhanced by right entrance
region of jet over northern Ontario across Quebec and any shortwaves
that will be sliding through. Heavier rain likely sets up farther
south of Upper Michigan closer to main sfc front and where MLcapes
over 1000 j/kg are located, but some heavy rain could affect south
half of cwa as that area is on gradient of h85 theta-e. Overall
there is fair agreement from the models in this scenario, though
exact placement of heavier rain remains uncertain.

Bigger question still remains on how quickly the front slips south
of area to bring dry weather on Fri. There has been little run-to-
run consistency in all models in whether front and associated
showers will be south of Upper Michigan or still lingering over at
least southern parts of cwa. At this time, GEM is most aggressive in
hanging onto qpf while last two runs of GFS and ECMWF would point to
mostly dry conditions as large Canadian high pressure builds in from
Manitoba and northern Ontario. More differences for Sat as ECMWF
continues to indicate qpf over far west and southwest cwa. Seems
these showers are tied to shortwave/q-vector convergence and h85
frontogenesis on edge of h85 thermal ridge. Trouble is that ECMWF is
not consistent with the solution as it has been back and forth on
this the last couple days. Ribbon of higher h85 RH quite narrow even
on the ECMWF focused over northern WI into sw Upr Michigan so think
it is overdone in showing broadbrushed and light qpf across much of
Upper Michigan in the 06z-18z time frame on Sat. Temps late this
week probably end up near to blo normal in the low to mid 60s,
coolest near Lk Superior with persistent northeast winds btwn the
high pressure over northern Ontario and sfc front to the south.

High pressure builds across the Great Lakes Sat and Sat night. Given
such an amplified pattern aloft, the sfc high may not move out of at
least eastern half of Upper Michigan until later Sun or Sun night.
Though timing is not set, the approaching upper level trough and sfc
trough along with low-level return flow on west side of retreating
high help will bring rain back to the area. Could be dealing with
moderate to heavy rain as pwats in the return flow regime are
forecast to top out over 1.75 inches as deep moisture flows north
off the western Gulf of Mexico. There are differences in how quickly
the sfc trough and axis of higher pwat cross Upper Michigan. This is
tied to how quickly shortwave trough moves across Upper Great Lakes
and what extent of shortwave energy is left out across the Central
Plains on Mon. Similar to late this week, run-to-run consistency on
these details in the models is lacking and agreement among the
models is also poor. Will keep using a consensus, which tilts
slightly toward quicker GFS, until these differences can be sorted
out. Though a slower solution would result in max temps Sun and
possibly Mon above normal in the 70s, will keep with consensus temps
mainly in the 60s due to the uncertainty in the timing for the

Front should be east of here on Tue leaving a breezy day with some
clouds and a few light showers eventually giving way to decreasing
clouds as high pressure begins to build back in from the west.

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 153 AM EDT WED SEP 21 2016

Although there wl be a good deal of mid clds at times and perhaps a
few -shra especially this aftn, dry llvl air wl ensure VFR conditions
prevail at all 3 TAF sites this fcst period. Thicker clds and more
numerous showers will arrive by this evng. While lingering near sfc
dry air wl likely maintain VFR conditions even if some showers
occur, MVFR conditions wl probably dvlp after 22/06Z.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 414 PM EDT TUE SEP 20 2016

West southwest winds to 25 knots will diminish to 20 knots or less
tonight into Wed as the pres gradient weakens with the Canadian low
lifting farther ne across Hudson Bay. Winds will remain blo 20 kts
into Saturday under a weak pres gradient across the Upper Lakes.
Southerly winds will increase Sunday to 20 knots as a low pressure
trough approaches from the west.

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


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