Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 201912

Area Forecast Discussion
National Weather Service Marquette MI
312 PM 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

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 night through Wednesday)
Issued at 311 PM EDT WED SEP 20 2017

High amplitude trough/ridge pattern setting up over the CONUS by the
end of the week will position the western Great Lakes in a south-
southwest flow which will likely result in record warmth across the
area from Fri through Sun. Best potential of pcpn across Upper MI
will occur early next week (at some point between Mon and early Wed)
as a slow-moving frontal boundary drifts across the Upper Lakes in
response to the eastward progression of the western CONUS mid-level
trough. Given the days of deep moist sw flow ahead of the trof and
fcst precipitable water values exceeding 1.5 inches or more than 200
pct of normal for this time of year, the potential will be there for
moderate to heavy rainfall as the front moves across the area.

Beginning Thu night...The front moving through the fcst area today
and tonight will lift back north Thu night/Fri morning as mid-level
trough deepens over the western CONUS. Could be some showers/t-
storms on the elevated 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 a better chance of seeing some convection

Friday through Sunday look to be unseasonably warm to record warm
days across the fcst area. As the warm front lifts well north of the
area Fri afternoon, warm advection in a ssw flow will bring 925-
850mb temperatures up to 20C or greater across the area. Mixing this
warmer air to the sfc will result in max temps 20 to 25 degrees
above normal for this time of year across much of the area on Friday
and possibly Saturday into Sunday as well with expected readings
in the mid to upper 80s over much of the western two thirds of
Upper Mi. Would not be surprised to see a few downsloping areas
along Lake Superior reaching 90F where compressional warming will
occur under southwest winds of 15 to 25 mph. Cooler 70s to lower
80s readings can be expected downwind of Lake Michigan. Southerly
flow in warm sector ahead of frontal boundary over the Plains will
also tap into Gulf moisture and bring low to mid 60s dewpoints
northward through the central CONUS into the Great Lakes region.
As a result, expect the increase in humidity to make for rather
muggy and uncomfortable conditions over the weekend. However, the
cap of warm air aloft will likely inhibit formation of convection
for the most part, despite the increase in moisture and
instability. By Sunday, model uncertainty increases regarding
progression of Plains frontal boundary eastward into Upper Mi. The
GFS is still the most aggressive pushing boundary eastward toward
western Upper Mi, while the ECMWF and GEM keep the stronger mid-
upper ridge intact with the frontal boundary farther west into MN.
Still possible there could be a few storms popping up over the
western cwa Sat night into Sun as frontal boundary draws closer
from the Plains. While there may be some increase in clouds to
keep max temps down a bit over the nw portion of Upper Mi on
Sunday, much of the cwa should still see plenty of sun to allow
for low to mid 80s readings away from the moderating influence of
Lake Mi.

Given strength of the eastern ridge in place, the slower frontal
progression of the ECMWF and Canadian models will likely be favored
over the quicker GFS solution. Slower solutions would argue that it
might not be until late Tue or early Wed that the front finally
clears Upper MI. As a result, Monday may trend drier across much of
the cwa while the better chance for showers and thunderstorms and
potential for locally heavy rain may be delayed until Tue with a
drying trend still expected Wed afternoon. Temps by Wed are expected
to cool back down to more seasonable late Sept readings.

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 206 PM EDT WED SEP 20 2017

KIWD: Gusty winds will diminish behind an approaching cold front.
Could see some rain along the front this afternoon. Fog is expected
tonight, but to an unknown extent.

KCMX: Worst conditions expected along and behind the approaching
cold front. Winds may be gustier than forecast over the next few

KSAW: Rain is expected (possibly with some thunder) this evening
along a cold front. Behind the front, fog is expected tonight. VIS
and CIG may be lower than currently forecast in the fog.

.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.

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


SHORT TERM...Ritzman
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