Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 241909

Area Forecast Discussion
National Weather Service Marquette MI
309 PM EDT SUN JUL 24 2016

Issued at 1034 AM EDT SUN JUL 24 2016

Much uncertainty still exists on the evolution of shower/TS
development today on slow moving cold fnt fcst to drift slowly acrs
Upr MI. However, 12Z INL/MPX raobs show a very capped environment,
with 12Z h7 temp as hi as 13C at MPX. Latest wv imagery shows this
mid lvl dry air moving E into the upr Midwest/Upr Lks with h7 W
winds as hi 35kt at MPX. Question remains whether this mid lvl
drying/warming wl be sufficient to cap the environment over Upr MI
even if ongoing clrg over the wrn cwa allows enuf insolation to
boost temps into the 80s ahead of the cold now aprchg wrn Upr MI.
Given the aggressive mid lvl warming/drying indicated by raobs/wv
imagery, favor the latest RAP guidance that suppresses convection
over the W half of the cwa but allows for some development this aftn
over the E, where merging lk breezes off Lk MI/Lk Sup enhance the
llvl convergence along the aprchg cold fnt and daytime heating in
the presence of lingering greater llvl mstr can aid destabilization.
Only concern in this area is if lo clds are more tenacious with sly
flow off Lk MI. Even with this lo cld potential, the RAP shows
muCape aprchg 1700j/kg over the interior E at 21Z. With deep lyr
shear near 40kts and sfc-h7 delta theta-e over 25C, any storms that
do dvlp in this area could turn severe.

.SHORT TERM...(Today and tonight)
Issued at 529 AM EDT SUN JUL 24 2016

Water vapor imagery and RAP analysis show a vigorous shortwave along
the Manitoba/Ontario border. Convection that spread from MN
yesterday se into northern IL/IN during the night has hindered more
substantial development farther n into the Upper Great Lakes. An
area of showers did consolidate into central Upper MI. Those shra
are now moving into the eastern fcst area. Latest RAP shows nose of
40kt low-level jet aimed into eastern WI, and that is where
shra/tsra have developed over the last few hrs. Meanwhile, line of
shra/tsra that developed ahead of occluded front in MN last evening
now extends from nw WI n into northern Ontario.

SPC meso analysis overnight has shown mucape increasing just ahead
of the shra/tsra approaching western Upper MI, so this convection
may hold together at least into the w half of Upper MI as it moves e
this morning. Not expecting this activity to pose a svr risk, but
gusty winds may occur along with brief hvy rain. Of much more
interest will be the potential of new convection to develop along
occluded front as it pushes across the area today. Compared to
yesterday, majority of model guidance has shifted new development
farther w into central Upper MI as opposed to eastern Upper MI as
vigorous mid level dry slotting and potential capping does not get
out ahead of the front. With front slicing thru central Upper MI
early to mid aftn, convective temps in the lower 80s being reached,
and mlcapes increasing to 1000-2000j/kg, expect isold/sct tsra
development to occur. Some high res model guidance veer winds more
sharply into n central Upper MI with lake breeze development as
gradient winds diminish near frontal boundary. So, Marquette county
may be the main initiation point for new convection this aftn with
development e and se from there. With deep layer shear of 40-50kt,
if storms develop, they will become well organized with some likely
to become svr. As was the case yesterday, models show impressive sfc-
mid level delta theta-e values of 30c or more, enhancing the risk of
damaging winds. While wet bulb zero heights are on the high end of
the range for favoring large hail, the likelihood of well-organized
storms due to healthy deep layer shear will support a large hail
risk. Expect a very uncomfortable, humid day today as dwpts push aoa
70F. Dwpts will begin to fall over the w this aftn.

Any lingering shra/tsra over the far eastern fcst area will end this
evening. Otherwise, expect mostly clear skies across the area

.LONG TERM...(Monday night through Sunday)
Issued at 304 PM EDT SUN JUL 24 2016

Decent agreement continues in overall look of upper level pattern
into next weekend. However, there still are model differences for
late this week into next weekend regarding position of shortwave
trough/sfc low and associated rain chances. Troughing that develops
early this week more or less persists at various amplitude through
the period. After a cool day on Mon could sneak in a warmer day Tue
ahead of a cold front that drops across Upper Great Lakes Tue night
into Wed. Temps should end up at or blo normal for the rest of the
week into next weekend, especially near Lake Superior with rather
persistent north-northeast winds.

Mon Night sfc high pressure slides across large area from northern
plains to Upper Mississippi river valley to the Great Lakes. PWAT
low enough for interior cool spots to drop into the low 50s while
shoreline locations stay in the 60s.

On Tue wnw flow aloft could brings in slightly falling heights but
at least now there is not any real shortwave to latch onto. Moisture
advection h7-h5 is main driver for rain showers moving into western
U.P. in the aftn. If there ends up being minimal shortwave energy
moving through, most day could end up dry with increasing mid-high
clouds from west to east. Cold front works through on Tue night.
Hints that stronger shortwave may move across as well. Should see
increase in shower chances on Tue night and with Upper Great Lakes
on edge of steeper mid level lapse rates there will be conditional
thunderstorm potential especially if stronger shortwave is crossing
the area. Front continues its passage across Upper Michigan on Wed.
Wind field is light so there may be lake breezes as front works
through. If fropa timing is slower as shown by GFS and ECMWF the
additional convergence and mlcapes up to 1000j/kg support increased
chances of showers and some thunderstorms as well. Effective shear
maybe up to 30 kts so likely not looking at severe storms.

Front settles across mid Mississippi river valley into the Lower
Great Lakes and northern Ohio Valley by Thu morning taking the
chances of rain with it. GFS shows stronger shortwave working
through Wed night into Thu morning so it is slower to clear out the
frontal zone and keeps pops lingering through at least Thu morning.
Cannot completely rule that out so will keep slight chances at that
time. High pressure then builds in for Friday while a sfc low
pressure wave slides across the lower Great Lakes and Ohio Valley
along slowing frontal boundary. Intstability will stay tied into the
low pressure wave and south of the increasingly stationary front
while airmass over Upper Great Lakes will be cooler and drier. Dry
weather should hold through Sat before the high moving east of the
region results in return flow bringing start of a warming trend
along with chances of showers and thunderstorms.

Caveat in this thinking is that 12z ECMWF now looks a bit more like
previous runs of GFS by showing deeper and farther north shortwave
trough and sfc low late Thu into Fri and maybe even into Sat. Result
would be rain could impact at least east half of cwa Fri into Sat.
For now, the forecast will stay dry for these time frames as that 12z
ECMWF run is quite inconsistent with its previous run.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 144 PM EDT SUN JUL 24 2016

Lingering lo clds/MVFR cigs at mainly CMX/SAW within very humid
airmass dominating the Upr Lks wl give way to VFR conditions
following the passage of a cold fnt/arrival of drier llvl air into
this evng. Gusty W winds wl continue at IWD and especially the more
exposed CMX location behind this fropa until some nocturnal cooling
this evng diminishes mixing. Although another upr disturbance wl
pass overngt, the incoming airmass wl be dry enuf to maintain VFR
conditions at all 3 sites. Some gusty WNW winds and diurnal cu wl
return with daytime heating on Mon, when a sharp pres gradient wl
linger btwn departing lo pres near James Bay and hi pres moving
toward MN.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 304 PM EDT SUN JUL 24 2016

In the wake of a cold front pushing across Lake Superior this aftn,
w winds of up to 20kt with gusts to 25kt are expected into Mon.
These stronger winds will diminish by Mon evening. Winds for the
remainder of the fcst period will mostly 15kt or less. Any fog
patches will diminish later this evening with the arrival of drier

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


SHORT TERM...Rolfson
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