Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 251916
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
316 PM EDT THU AUG 25 2016

.SHORT TERM...(Today and tonight)
Issued at 522 AM EDT THU AUG 25 2016

Water vapor imagery and RAP analysis show a strong mid/upper level
ridge over the Gulf of Alaska with downstream trof extending from
Hudson Bay to the Dakotas. A shortwave is noted within the trof over
southern Manitoba. At the sfc, a trof extends from se Manitoba to
just s of James Bay. The shortwave and sfc trof will be the main
features of interest in the short term.

Shortwave over southern Manitoba is fcst to shift e, passing over
far northern Lake Superior and adjacent northern Ontario this
evening. Meanwhile, sfc trof will slowly drift s today before
picking up speed this evening with passage of shortwave. Per q-
vectors, deep layer forcing for upward motion associated with
shortwave will pass by to the n of Upper MI today. This should lead
to sct to nmrs shra and perhaps some tsra along and in the vcnty of
the sfc trof which will remain n of Lake Superior this aftn. Thus,
do not expect any pcpn across the fcst area today. Expect a mostly
sunny day with fcst soundings indicating some cu development this
aftn. Based on mixing heights on fcst soundings, high temps for much
of the area will be in the mid/upper 70s, with some lower 80s over
the central, especially south central, under downsloping westerly
winds. Dwpts will fall back to more comfortable levels in the 50s.
Some interior locations will drop toward a much more pleasant 50F.
Finally, tightening pres gradient ahead of sfc trof and deepening
mixed layer with daytime heating will lead to gusty winds this aftn,
especially over the Keweenaw under a favorable westerly wind
direction. Expect gusts to around 35mph there, perhaps higher if
some model guidance is on track with potential to tap 35-40kt winds
aloft.

Sfc trof will drop s across Upper MI tonight. With shortwave
tracking into southern Quebec, subsidence/deep layer q-vector
divergence overspread the sfc trof as it moves s across the fcst
area. Thus, while shra will be occurring in the vcnty of the trof
today, those shra should fall apart before reaching the area tonight
given the loss of support from shortwave and loss of diurnal
heating. However, the rather sharp wind shift associated with the
sfc trof combined with 850mb temps falling to around 7C by 12Z Fri
overtop lake sfc waters running near 20C may be sufficient to
generate a few lake effect -shra over the western into portions of
the n central fcst area late tonight into Fri morning.

.LONG TERM...(Friday night through Thursday)
Issued at 315 PM EDT THU AUG 25 2016

Recent model runs have trended faster at brining a return of deeper
mstr/pcpn to the area late Fri ngt/Sat ahead of a shrtwv aprchg thru
MN on Sat. With this faster trend, Sun now looks to be the drier day
of the upcoming weekend. A WNW flow aloft to the E of a bldg upr rdg
in the Plains will dominate the wx pattern next week. A disturbance
embedded in this flow wl track fm Scentral Canada into Quebec early
next week and drag a cool fnt across the cwa Mon ngt/early Tue. More
sgnft extended model differences are then the rule the second half
of next week.

Fri ngt...Although the night wl start off on the tranquil side with
sfc hi pres rdg/mid lvl dry air in place, a SW flow aloft ahead of
an aprchg shrtwv in the Nrn Plains is fcst to draw more moisture
into the Upper Lks later at ngt. The result wl be incrsg clds, and
perhaps some showers near the WI border toward 12Z.

Sat/Sat ngt...Arrival of dpva/isentropic ascent on the 305K sfc/deep
lyr qvector cnvgc/deep mstr ahead of aprchg shrtwv wl cause an area
of more nmrs/wdsprd showers to move into the Upper Lks. There are
still some inconsistencies among the guidance on the strength/track
of accompanying sfc lo pres and location of greater qpf, so tended
toward a consensus of the guidance. While there are differences on
the track/qpf, models have overall trended toward a faster solution.
So tended to bring pops in faster on Sat and then dry out the fcst
quicker on Sat ngt. Plenty of clds on Sat and h85 temps not far fm
12C to the N of sfc warm fnt wl greatly hold down max temps on Sat.

Sun...There could be some lingering mrng lo clds, but arrival of
dnva/deep lyr qvector dvgc/larger scale drying/sfc hi pres during
daytime warming ahead of trailing shrtwv rdg wl bring a return of
some sunshine during the day. H85 temps in the 12-14C range wl allow
for max temps into the 75-80 range away fm some cooling downwind of
mainly Lk Sup with WNW h925 winds. The hiest temps wl be over the
Scentral, where this WNW flow wl downslope.

Early next week...The medium/extended range guidance advertises a
WNW flow aloft over the Great Lks to the E of a bldg upr rdg in the
Plains wl dominate the wx pattern. There is decent agreement a
shrtwv/sfc lo wl tracking thru Scentral Canada on Mon will drift
across nrn Ontario and into Quebec on Mon ngt/Tue. Although there
could be some showers/TS as early as Sun ngt in the WAA ahead of
this feature and as the attendant cold fnt drifts thru the Upr Lks
on late Mon/early Tue, passage of the stronger dynamic forcing to
the N should limit pops over Upr MI. Temps early next week should
average aoa normal.

Extended...Although the longer range guidance points toward a bldg
mean upr rdg in the Plains, there are some sgnft differences among
the explicit longe range models on how far to the S a Canadian hi
pres wl settle in the more or less NW wind component to the E of the
upr rdg axis. While the 00Z ECMWF showed a hier amplitude trof over
ern Canada/a sharper NW flow into the Great Lks/farther S track of
the sfc hi pres into NW Ontario late in the week, recent GFS runs
indicate a more WNW flow wl prevail in Ontario to the E of the upr
rdg axis and allow a warm/humid SW flow arnd sfc hi pres over the SE
Conus to dominate the Upr Lks just to the S of a W-E oriented stnry
fnt just N of Lk Sup. The GFS fcst scenario would support above
normal temps/chcs for showers and TS while the ECWMF fcst would
result in aob normal temps/mainly dry wx except when that model
shows another shrtwv digging thru the Upr Lks on Thu. Considering
the sharp differences/plausible outcomes, wl maintain the consensus
fcst for now.
&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 141 PM EDT THU AUG 25 2016

A trough will drop through the area tonight. Behind it, MVFR cigs
should develop at all TAF sites late tonight into Friday morning.
Not out of the question that cigs could fall to IFR at KIWD.
Conditions will begin to improve Friday afternoon.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 522 AM EDT THU AUG 25 2016

Ahead of an approaching sfc trof, expect wsw winds to increase to 20-
30kt over much of the the w half of Lake Superior today. Over
eastern Lake Superior winds will be lighter, probably even dropping
blo 10kt and becoming vrbl this aftn over portions of s central Lake
Superior as lake breeze circulation develops. Stronger winds up to
20-25kt will then quickly develop this evening before winds diminish
to blo 20kt across the entire lake late tonight into Fri morning
after passage of the sfc trof. Winds will diminish further to mostly
under 15kt on Fri as high pres briefly builds over the area. Winds
will be mostly under 20kt thru the weekend under a weaker pres
gradient.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...Rolfson
LONG TERM...KC
AVIATION...Titus
MARINE...Rolfson



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