Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 201049
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
649 AM EDT Wed Sep 20 2017

.SHORT TERM...(Today and tonight)
Issued at 329 AM EDT WED SEP 20 2017

Upper-level clouds continued to stream eastward across Upper
Michigan ahead of the MCS tracking east-northeast across Minnesota
this morning. The cold front that originally initiated this
convection has now just begun to push into western portions of
Minnesota this morning. Further to the east, across central and
eastern portions of Upper Michigan stratus has begun to develop
and/or lift northwest this morning. A few areas may see some patchy
fog this morning, especially in areas that see light winds and
upslope conditions.

Today there are a few forecast concerns, including the potential for
multiple rounds of showers and storms across the west and central
(one this morning and then another round later in the afternoon) and
strong and gusty winds ahead of the cold front expected to arrive
later today. A few storms this morning and later this afternoon
could be strong to severe, with the main hazard being strong
downburst winds.

Through the morning hours, winds will increase ahead of the
advancing cold front and become quite gusty across the east. Ongoing
convection in Minnesota looks like it will make its way into western
portions of Upper Michigan. Given the enhanced low-level winds ahead
of the convection wouldn`t be surprised if a few storms produce
strong to severe wind gusts. However, as the axis of better MUCAPE
values continue to drop south of the area with the 850mb flow
veering out and the main shortwave lifts north across the Arrowhead
of Minnesota, convection is expected to gradually weak across the
west, and possible making it into central portions of Upper Michigan
through the morning hours.

Through the rest of the day, ahead of the cold front the primary
concern will be the potential for strong and gusty south-southwest
winds. With gusty gradient winds already present ahead of the cold
front this morning, expect this trend to continue as it pushes
through the region later today. Overall, models are in good
agreement with 925mb flow of around 40 knots just ahead of the cold
front. Therefore, with the front expected to push eastward across
Upper Michigan during the daytime hours, the combination of mixing
and gradient flow should allow wind gusts to approach at least the
30 to 40 mph at times. These winds gusts will be possible through
the morning hours across the west, and then central and eastern
during the afternoon and into the evening hours. Thankfully it does
look like this corridor of strong and gusty winds will only linger
for a few hours as it remains fairly transient. The only condition
that may limit how strong wind gusts get is the cloud cover
expected, which will hinder diurnal heating slightly and therefore
the depth of turbulent mixing.

As the cold front pushes eastward across Upper Michigan strong to
severe storms remain possible, primarily across the west and central
portions of the area. There is some uncertainty in the coverage and
overall intensity of convection given the ample cloud cover expected
ahead of the front; however, as a subtle shortwave is progged to
lift across the area this should be enough support to initiate
scattered storms along the cold front later this afternoon and
evening. CAPE profiles are not terribly impressive, but with a
plethora of dry air and enhanced low-level flow the main hazard
looks to be strong to severe downburst winds. Given the amount of
deep-layer shear and its quasi-perpendicular orientation to the
front, if storms can remain organized/rotate a hail threat will also
possible.

Tonight, 850mb flow veers our rather rapidly so expect ongoing
thunderstorms to diminish in coverage and intensity across the east.
As a post frontal, cooler and more stable airmass moves in
immediately behind the front, light winds and clearing conditions
should give way to radiational fog across the west and central.
Patchy areas of dense fog will be possible, especially in areas that
see rainfall later today.

.LONG TERM...(Thursday through Tuesday)
Issued at 448 AM EDT WED SEP 20 2017

A remarkably warm period is expected Fri thru Sun with a number of
locations likely seeing record breaking late season warmth. Not only
that, some locations may see max temps that have never been so high
this late in the year. This warmth will be the result of the long
advertised strong amplification of a western CONUS trof and
downstream eastern N America ridge. 500mb height anomalies in the
western trof will peak close to 300m today over the Pacific NW. As
the trof digs southward thru Fri, heights will build over eastern N
America. A +230m anomaly will be centered s of James Bay during the
weekend. Resulting deep sw flow into the Upper Lakes will send 850mb
temps to 12-14C above long term late Sept averages, setting the
stage for record breaking warmth Fri-Sun which will be combined with
uncomfortable mid summer type dwpts readings. Next week, the western
trof will weaken substantially while progressing downstream,
reaching the Great Lakes during the middle of next week. So, while
this will obviously bring cooler weather, conditions next week will
only fall back to seasonable levels for late Sept. As for pcpn,
nearly stationary front will be setting up from the Plains to
northern Ontario between the western trof and eastern ridge. Pcpn
potential here will depend on how close to Upper MI this front is
located and whether any shortwaves ejecting from the trof pass close
to the area. Right now, it appears there will be some chc of pcpn
Thu night into early Fri as warm front lifts n. Then, proximity of
the nearly stationary front to western Upper MI will put that area
at some risk of shra/tsra thru the weekend. Best potential of pcpn
across Upper MI will occur early next week (at some point btwn Mon
and early Wed) as frontal boundary drifts across the Upper Lakes in
response to progression of the western CONUS mid-level trof. Given
the days of deep sw flow ahead of the trof, potential will be there
for mdt to hvy pcpn as front moves across the area.

Beginning Thu, expect a dry day as weak sfc high pres moves across
the area in the wake of tonight`s fropa. Only issue may be fog near
the shorelines of the Great Lakes. Diminishing advection of drier
air as the weak high pres quickly follows fropa may allow any fog
that develops over the waters today thru this evening to linger on
Thu under light wind regime. At this time, it appears the best
potential for fog would be along the Lake Michigan shoreline and
also the Lake Superior shoreline from the Keweenaw eastward. High
temps on Thu should be mostly in the low/mid 70s, locally a little
cooler lakeside.

The sw end of the front that passes tonight will lift back n Thu
night/Fri morning as trof deepens over the western CONUS. Could be
some shra/tsra on the 850mb cape gradient as it lifts nne in
conjunction with low-level jet. Nose of low-level jet suggests the
western and northern fcst area has better chc of seeing some
convection overnight.

Assuming warm front lifts n of the area, Fri will be unseasonably
warm, hot really for this time of year, under 850mb temps of 20C and
increasing sunshine. Except on the Keweenaw where winds may stay
somewhat backed off the lake, mid to upper 80s seem quite likely
over the w half of Upper MI. Locations where ssw winds are
downsloping may reach 90F. Will obviously be cooler downwind of Lake
Michigan over the eastern fcst area...70s to lower 80s. This
unseasonable warmth will continue over the weekend with strong mid-
level ridge across the Great Lakes region. Sat could be just as warm
as Fri under similar air mass. Temps aloft drop slightly on Sun, so
probably not quite as warm as Sat. One factor that could affect
temps is if frontal boundary sags s and e a little. If it does, far
w and nw Upper MI will see some cooling, aided by wind off the lake.
With dwpts into the 60s, nighttime lows will be equally as anomalous
as the daytime highs. Expect some record high mins to be set. Not
out of the question that some downslope locations won`t fall much
blo 70F Fri night and Sat night. After the potential of shra/tsra
Thu night into Fri morning, much of the fcst area should be capped
thru the weekend. Any shra/tsra should be confined close to the
nearly stationary frontal boundary to the w and nw. Schc/low chc
pops will be utilized over the far western fcst area thru the
weekend.

Given the strength of the eastern ridge, will generally favor the
slower frontal progression depicted by the ECMWF during the first
half of next week. May not be until late Tue or early Wed that the
front finally clears Upper MI. Fcst will show increasing shra/tsra
chances Mon into Tue, then a trend to dry weather on Wed. Temps by
Wed will be back down to more seasonable late Sept readings.
&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 649 AM EDT WED SEP 20 2017

Challenging aviation forecast this morning with low clouds streaming
northward ahead of a cold front currently moving across central
Minnesota, and a line of showers and thunderstorms pushing into
western Upper Michigan this morning. Expect this line of showers and
storms to impact KIWD and KCMX this morning. At KSAW, expect the low
ceilings to persist through much of the day, but they should
gradually lift into the MVFR category later today as winds begin to
increase. Gusty southerly winds will impact terminals today, with
periodic gusts upwards of 30 knots at times. Another round of
thunderstorms is possible later today, but coverage isn`t certain so
have only included mentions of VCTS within TAFs for now. Could see
fog develop tonight as high pressure quickly moves into the area.
Have trended visibilities down at at all terminals tonight into
early Thursday morning to account for this possibility.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 338 AM EDT WED SEP 20 2017

Early this morning thunderstorms are expected to move across western
portions of the lake, a few could be strong to severe with winds
being the primary hazard, along with dangerous lightning. Winds will
remain around 20 to 30 knots ahead of a cold front approaching from
the west today. A few locations across the central and eastern
portions of the lake could see gale force gusts to 35 knots at times
this afternoon. However, confidence is low in regards to how
persistent these gusts will be. As the cold front pushes east across
the area this afternoon and evening, winds will decrease to around
10 to 20 knots. Behind the front, we may see fog develop tonight and
linger into Thursday. Friday through early next week, winds look to
remain between 15 and 20 knots.
&&

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

$$

SHORT TERM...Ritzman
LONG TERM...Rolfson
AVIATION...Ritzman
MARINE...Ritzman



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