Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 241744

Area Forecast Discussion
National Weather Service Marquette MI
144 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 through Saturday)
Issued at 503 AM EDT SUN JUL 24 2016

Monday and Monday night: The upper level 500mb trough and surface
trough will continue eastward through this time period as high
pressure slides into the area. Aloft zonal flow will slide across
the Upper Great Lakes by Monday afternoon.  Dry air, shown in the
1000-500mb layer, will keep skies mostly clear through this time
period with much more comfortable humidity levels along with
coolerhigh temperatures. The pressure gradient ahead of the surface
ridgewill favor a west-northwest flow across Lake Superior with
gusts upto 25 mph. This will create a moderate to high swim risk for
beachesalong the Alger County shoreline.

Tuesday through Wednesday night: A cold front is progged to sag
southward from Canada into the Upper Great Lakes Region as the
surface high slides to the east. Southerly flow on the back side of
the high will help to increase moisture into the area. This, along
with forcing along the front will provide chances of showers and
thunderstorms for most of the CWA through this time period as the
weak cold front stalls across or just south of the area by Wednesday
night. MUCAPE values are not overly impressive, generally progged to
be around 500-750 J/KG Tuesday afternoon/evening and again Wednesday
afternoon/evening. Severe weather potential is looking very low at
this point, through the entire time period, as the system will lack
any major dynamical support. Shear values are progged to remain
around or below 20 knots through this forecast period. Details will
be ironed out as we move closer; however, at this point, it is not
looking too favorable for severe weather.

Thursday through the extended: Model solutions begin to diverge, as
is typical this far out, but the general trend will be for more of a
troughing pattern across most of the eastern CONUS with upper level
ridging building across the western CONUS. This would keep the Upper
Great Lakes cooler with embedded shortwaves sliding thorough the
area during this time period. Overall confidence in any one specific
model remains fairly low with timing/strength of the aforementioned
waves; therefore, will stick closely to model consensus which keeps
small chances of showers intermittently through Thursday through

.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 AM Lake Superior forecast issuance)
Issued at 529 AM EDT SUN JUL 24 2016

In the wake of a cold front pushing across Lake Superior today,
expect w winds to increase up to 20kt with gusts to 25kt from w to e
this aftn/evening after it passes. These stronger winds will persist
into Mon morning before gradually diminishing. Winds for the
remainder of the fcst period will mostly be at or blo 15kt.

Humid air mass over the area ahead of the passing cold front may
allow patchy fog to develop today.

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


SHORT TERM...Rolfson
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