Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 260817

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

.SHORT TERM...(This evening through Tuesday)
Issued at 401 PM EDT MON SEP 25 2017

Water vapor imagery and RAP analysis show that pattern progression
is beginning. Deep trof that has been over the western CONUS is
weakening and shifting downstream. Strong ridge that has been over
eastern N America remains. However, main positive anomaly center
that had been s of James Bay has started to weaken and drift se.
Btwn the trof and ridge, deep sw flow is continuing into the Upper
Great Lakes today. At the sfc, nearly stationary front that has
lingered generally just w of Upper MI for the last couple of days
has slipped e into western Upper MI. Lake breeze component has also
assisted the front in dropping s into n central Upper MI this aftn.
Under mostly sunny skies ahead of the front, MLCAPES have increased
to 500-1000j/kg over central Upper MI per latest SPC mesoanalysis.
The instability and low-level convergence provided by front will set
the stage for convection, which is just starting to develop, to
expand over the next few hrs. Farther w behind front, areas of shra
have been spreading from IA to western Lake Superior today. Ahead of
the front, temps are again unseasonably warm with mid/upper 80s away
from Lake Michigan moderation. Behind the front, current temps are
in the 60s far w.

Instability along with convergence provided by frontal boundary will
generate sct to nmrs shra/tsra in the vcnty of the front this
evening across basically the nw half of the fcst area. With deep
layer shear on the order of 25-35kt and mlcape upwards of 1000j/kg,
an isolated svr storm or two will be possible for the next few hrs.
Otherwise, very hvy rainfall is likely with any of the storms thru
the evening due to precipitable water around 1.5 inches (upwards of
250pct of normal) and freezing level at 12000ft or higher. The
evening convection will tend to fade away late evening into the
overnight as instability diminishes. Focus of shra should then tend
to shift farther w where fgen and better deep layer forcing will
provide support for pcpn just ahead of and w of sfc low pres wave
which will be tracking nne toward nw WI late tonight.

On Tue, as sfc low pres lifts across far western Upper MI and out
over Lake Superior, cold front will sweep e thru the day. Thru the
morning, shra will continue to be most widespread over far western
Upper MI along and w of sfc low track. If there is enough heating
ahead of the front, isold svr storms are not out of the question
over the eastern fcst area in the aftn given 30-40kt of deep layer
shear. Will be something to keep in mind if there isn`t much in the
way of cloud cover thru the morning to hold temps/instability down.
High temps should range from the 60s w to the upper 70s/around 80F

.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 06Z TAFS through 06Z Tuesday night)
Issued at 244 AM EDT TUE SEP 26 2017

Continue high confidence of IFR to LIFR conditions for much of the
TAF period due to ample low level moisture ahead of a low pressure
system. Conditions should improve after the low moves through late

.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...


SHORT TERM...Rolfson
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