Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 261139

Area Forecast Discussion
National Weather Service Marquette MI
739 AM EDT Tue Sep 26 2017

.SHORT TERM...(Today and tonight)
Issued at 503 AM EDT TUE SEP 26 2017

WV imagery and RAP analysis indicated a mid/upper level low over the
wrn Dakotas embedded in a large trough over the wrn CONUS.
Southwest flow prevailed through the wrn Great Lakes between the
trough and a ridge over the ern Great Lakes and mid Atlantic states.
At the surface, a broad area of low pressure extended from WI into
ern IA. A large area of rain from cntrl IA through ern Mn and nw WI
into wrn Lake Superior was supported by deep layer qvector conv
ahead of a shortwave from ern South Dakota into ern Nebraska and
upper level div with the right entrance of the 250-300 jet through
nrn Ontario. Farther east, mainly isold/sct shra were moving
through ne WI into cntrl Upper Michigan.

Today, as the sfc low deepens and lifts through cntrl Upper
Michigan into ern Lake Superior, it will drag a cold front across
the cwa. Although the heavier pcpn associated with 850-700 mb fgen
will remain over wrn Lake Superior, expect increasing shower
coverage over area as a shrtwv and front move through the area.
Cloud cover will be thick enough to limit heating/instability but
with temps into the mid and upper 70s where some sunshine is more
likely over the cntrl and east, MLCAPE values may climb into the
500- 000 J/Kg range. With 0-6km shear values near 40 knots some
strong storms near svr thresholds may be possible even with the
marginal instability.

Tonight, shra/tsra chances over the east half during the evening
will diminish quickly overnight as cooler/drier air moves in behind
the front. There may be enough low level moisture along with
increasing upslope wnw flow to support isold -shra/-dz over the
west, mainly over the higher terrain.

.LONG TERM...(Wednesday through Monday)
Issued at 417 AM EDT TUE SEP 26 2017

Wednesday and Wednesday night: A surface ridge and drier air will
push into the area for this time period, which will lead to mainly
dry conditions across much of the area under near normal
temperatures. Highs will be in the upper 50s to around 60. Lows will
be mainly in the 40s with a few upper 30s possible inland west.

Thursday through Friday, models now have similar solutions with the
next wave of energy as it rotates into the Upper Great Lakes region
through this time period. Aloft the 500mb trough is expected to
slide from northern Ontario Thursday morning to the lower Great
Lakes by Friday afternoon. The associated surface low will follow a
very similar course through the same time period. As these features
cross the area, moisture and forcing will increase, bringing
scattered rain showers to much of the area. After the wave shifts
out of the area Friday afternoon, the showers should slowly taper
off from the northwest. Outside of the rain shower potential,
temperatures will cool off significantly from where they`ve been
over the past few days. In fact most places will be near to below
normal by the end of the work week. High temperatures will fall into
the low to mid 50s by the end of the work week.

Friday night through the upcoming Weekeend: The trough will continue
to shift east of the area as high pressure builds back into the U.P.
allowing for warming temperatures aloft along with drier air to
filter into the area. This will lead to a mainly dry forecast for
the U.P. As the high shifts directly overhead Friday night into
Saturday morning, skies will clear and winds will become calm. This
will set the stage for ideal radiational cooling conditions. In
fact, many locations in the U.P. may end up seeing frost late Friday
night into Saturday morning as temperatures drop into the low to mid
30s. Wouldn`t be surprised to see a few upper 20 degree readings in
the typically cooler spots of the inland west.

Rest of the extended: A front is expected to approach the area by
late in the day Monday, which may lead to some showers and
thunderstorms. At this time, due to timing issues with the
approaching front, will stick with a consensus of the models,
introducing scattered showers and thunderstorms for Monday afternoon
into Monday night. Tuesday, depending on how fast/slow the front
passes, may end up being dry.

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 739 AM EDT TUE SEP 26 2017

High confidence for IFR to LIFR conditions remains this morning due
to ample low level moisture ahead of a low pressure system.
Conditions should improve after the low moves through late today
especially at KSAW where a more downslope wrly component prevails.
Otherwise, conditions will be slower to lift to MVFR at KIWD and

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 401 PM EDT MON SEP 25 2017

A wave of low pres will lift nne late tonight/Tue along a frontal
boundary extending from the Plains to the Upper Great Lakes. This
will result in ne wind increasing to 20-30kt over western Lake
Superior tonight into Tue morning before diminishing in the aftn.
Winds will remain lighter over eastern Lake Superior. As the low
lifts ne of Lake Superior Tue evening, nw winds will increase to 20-
30kt across the lake Tue night into Wed with the strongest winds
over eastern Lake Superior. Winds will diminish to mostly under 20kt
Wed night into Thu. A low pres trof swinging se across the Upper
Great Lakes Thu night will usher in another round of 20-30kt winds
on Fri. Not out of the question that there could be a few gale force
gusts to 35kt over mainly the central portion of Lake Superior.
Winds will then diminish to under 20kt for Sat.

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


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