Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 161857
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
257 PM EDT Sat Sep 16 2017

.SHORT TERM...(This evening through Sunday)
Issued at 257 PM EDT SAT SEP 16 2017

Early morning clouds pushed east of the area, and has resulted in a
partly sunny afternoon. Southerly flow has allowed surface
conditions to warm back above seasonal conditions with highs in the
upper 70s to lower 80s. Morning convection upstream across Wisconsin
has since weakened, but the cloud remnants are beginning to approach
the western Upper Peninsula. Dewpoints are also remaining elevated
this afternoon in the lower to middle 60s, resulting in some
increased humdity. For the remainder of this afternoon and evening
clouds will be on the increase. The trough of low pressure that has
produced the clouds and precip will slide north/northeast across
Northern Minnesota into Western Ontario. Instability late this
afternoon and early evening does not look overly exciting, but there
could be enough to support a few stronger storms to develop mainly
along the western half of the U.P.

The wrinkle or challenge for strong development could be the path of
the low pressure, which would place the U.P. in a slightly more
diffluent zone and the environment could be less favorable later
this evening. Nonetheless the dynamics/forcing could still warrant a
few storms through tonight from west to east, ending shortly before
daybreak Sun across the eastern U.P. Overnight lows will once again
remain mild due to the thick cloud cover and areas of rain. So have
lows in the upper 50s to lower 60s, but this could be more low/mid
60s.

Frontal boundary will be progressive and push thru the U.P. by mid-
morning Sun, ushering in slightly cooler and more seasonal airmass
to the U.P. with highs Sun afternoon in the 60s to lower 70s. The
pressure gradient will tighten slightly and could produce some gusty
winds at times through the afternoon, then decrease closer to sunset
Sun.

.LONG TERM...(Sunday through Friday)
Issued at 505 AM EDT SAT SEP 16 2017

With regard to the big picture, last 24hrs of medium range model
runs remain in good agreement with recent days runs. For roughly the
next 7 days, a mean trof will be set up over the western CONUS into
adjacent western Canada with downstream mean ridging over eastern N
America. Pattern will become quite amplified with 500mb height
anomalies in the trof and ridge reaching upwards of 250m in the mid
and late part of the upcoming week. Under sw flow btwn the trof and
ridge, warm conditions/above normal temps will dominate the Upper
Great Lakes on most days with coolest conditions (around normal)
Mon. One or two days will likely be unseasonably warm. Next weekend
into the early part of the following week (7-10 day period),
guidance points toward progression of the pattern, but given
strength of the eastern ridge, progression may be slow. In any
event, western trof should weaken considerably as it shifts e. So,
while cooler weather will return in 7-10 days, conditions will be
seasonable for what will be late Sept. As for pcpn, a more
significant shortwave lifting out of the mean western trof toward
Hudson Bay will push cold front across the area later tonight and
Sunday, bringing at least sct shra/some thunder. Following fropa,
dry weather will return Sun night into at least Mon morning. Under
wsw flow, another weaker shortwave may affect the area Mon
night/Tue, providing some potential of pcpn. Then, with trof
becoming amplified over the western CONUS, pcpn mid and late week
will depend on whether any of the shortwaves lifting out of the trof
track close enough to Upper MI to spread pcpn across the area. Given
the deep sw flow, the Upper Lakes at some point should have the
potential for decent rainfall as the trof eventually drifts e,
especially if the associated cold front is slow moving as it passes
across the area.

Beginning Sunday, vigorous shortwave over northern MN early in the
day will lift into northern Ontario. Associated cold front should be
extending across central Lake Superior/central Upper MI at 12z. With
best height falls and strongest deep layer forcing per q-vectors
lifting ne well to the nw of here, coverage of shra and some thunder
along/just ahead of front will likely diminish thru the morning hrs
as the front continues eastward. If there is sufficient heating
before front clears the eastern fcst area, there may be an uptick in
convection. Behind the front, skies will become mostly sunny.
Despite fropa, temps will still be above normal over the central and
eastern fcst area. Max temps should range from low 60s far w to the
mid 70s s central. Will be a breezy day on the Keweenaw under
favorable post-frontal westerly winds and decent mixing. Expect
gusts to 30-35mph there.

With sfc high pres building over the Upper Lakes on Sunday night, it
will be a quiet/cool night. May see some frost in the interior as
temps fall into the mid 30s for at least the traditional cold spots.

While weakening sfc high pres lingers over the Upper Lakes on Mon,
models still show a shortwave approaching in continued sw flow
aloft. While the last 2 days of model runs have showed this
shortwave, area impacted by associated shra and timing of pcpn
(whether arriving on Mon or Tue or affecting both days) is still not
well agreed upon. At this point, will utilize a consensus of recent
model runs to construct fcst, resulting in schc/low chc pops late
Mon into early Tue.

Mid and late week, deep trof will set up over the western CONUS.
Model trends show the ECMWF trending toward the CMC and especially
GFS idea of a lead shortwave swinging out of the deepening trof and
across MN into northern Ontario Wed/Wed night. As a result, fcst
will reflect a chc of shra late Tue night into Wed night. Once
timing becomes more certain, period of potential shra will be
narrowed into a shorter time frame. Shra chances from Thu thru next
weekend will deepend on the uncertain timing/track of shortwaves
lifting out of the western trof and on the eventual progression of
the trof. Deep sw flow and the likelihood of a slow moving sfc
frontal boundary associated with the trof are suggestive of the
potential of mdt/hvy pcpn at some point. This pcpn could be enhanced
by remnant moisture from current Hurricane Norma off the w coast of
Mexico if it gets captured by the western trof.
&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 257 PM EDT SAT SEP 16 2017

Mainly VFR conds will persist through this evening; however, with
increasing clouds from the west/southwest to east and precip chances
steadily increasing later, cigs will thicken and slowly lower from
west to east towards MVFR conds. Guidance has backed off on
confidence to thunderstorm chances and coverage will continue to
remain low. Expect periodic thunderstorms between 00-04z for IWD,
and 01-06 at CMX, and 03-07Z at SAW. Then some lingering showers
will come to an end around 12-14z, ending earlier at IWD and CMX.
With cigs slowly lifting as drier air and breezy conditions develop.
Expect winds to shift from southeast to southwest then shift to the
west/northwest.

&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 257 PM EDT SAT SEP 16 2017

Winds of 20 to 30 knots will persist through this afternoon, but
with clouds increasing expect winds to diminish to 10 to 20 kt later
this evening from the south/southwest.

By Sunday morning, expect the winds to pick back up to around 20 to
30 knots as a cold front pushes east across the lake. Winds will
relax to around or less than 15 knots by early Monday morning
through Tuesday. By Wednesday winds will increase to 20 to 25 knots
briefly, and then will be around 20 knots through the end of next
week.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Beach Hazards Statement until 9 PM EDT this evening for MIZ014.

Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...Beachler
LONG TERM...Rolfson
AVIATION...Beachler
MARINE...Beachler



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