Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 251142

Area Forecast Discussion
National Weather Service Marquette MI
742 AM 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

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 through Wednesday)
Issued at 319 AM EDT THU AUG 25 2016

Nam shows a deep trough over the western U.S. and Rockies 12z Fri
which moves into the northern Plains by Fri night and into the upper
Great Lakes Sat night. Nam shows some 850-500 mb q-vector
convergence and deeper moisture moving through the area on Sat into
Sat night.

Did not make too many changes to the going forecast. Cannot rule out
some pops for Fri morning across the western and central cwa. Did
bring in some pops across the far southern cwa late Fri night with
slight chances and went likely pops for Sat for the southern and
central cwa with chance pops elsewhere. Could see up to an inch of
rain from late Fri night into Sat night across the cwa with the
heaviest amounts across the south and east.

In the extended, GFS and ECMWF show a 500 mb trough over the upper
Great Lakes 12z Sun. This shortwave trough dampens out and the upper
Great Lakes becomes zonal 12z Mon with sfc high pressure across the
area. A 500 mb ridge starts to build into the upper Great Lakes 12z
Tue with a sfc front over the area 12z Wed. Temperatures look to
stay above normal for this forecast period.

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 742 AM EDT THU AUG 25 2016

VFR conditions are expected at KIWD/KCMX/KSAW into the evening hrs
under a relatively dry air mass with nothing more than some diurnal
cu. A gusty west wind up to around 30kt is expected at KCMX this
aftn under a tightening pres gradient ahead of an approaching sfc
trof. That trof will drop thru the area tonight. Behind it, MVFR
cigs should develop at KIWD late tonight and possibly at KCMX as
well. Not out of the question that cigs could fall to IFR at KIWD at
the end of the fcst period. MVFR cigs will arrive at KSAW just
beyond this fcst period.

.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

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


SHORT TERM...Rolfson
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