Area Forecast Discussion
Issued by NWS Marquette, MI

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000
FXUS63 KMQT 171811
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
211 PM EDT Sun Sep 17 2017

.SHORT TERM...(Today and tonight)
Issued at 543 AM EDT SUN SEP 17 2017

Water vapor imagery and RAP analysis show a vigorous shortwave
lifting thru se Manitoba and adjacent MN/northern Ontario.
Associated cold front cuts across far western Upper MI with sct to
nmrs shra and some thunder along/ahead of it. After an unseasonably
warm and humid day yesterday, conditions continue to be unseasonably
warm across Upper MI early this morning with temps in the 60s to
around 70F and dwpts in the 60s, much more typical of mid summer.

Cold front will continue to sweep eastward today, exiting the
eastern fcst area early this aftn. Will generally carry sct shra and
some thunder eastward with the front. With arrival of drier air
after fropa, clouds will begin to clear out with skies becoming
sunny across at least the w half of Upper MI by 18z. Given the very
warm start to the day for this time of year, max temps will still be
above normal today over the central and eastern fcst area despite
fropa. Max temps should range from low 60s far w to the mid 70s s
central. However, temps over the eastern fcst area, especially
closer to Lake Superior, should fall into the lower 60s rather
abruptly this aftn as winds shift to the nw off Lake Superior. Will
be a breezy day on the Keweenaw under favorable post-frontal
westerly winds and decent mixing. Expect gusts to 30-35mph there.
Finally, waves are sufficently high from ongoing southerly flow to
lead to a mdt swim risk for the Lake Michigan beaches of Schoolcraft
County today, though that risk will diminish this aftn as winds
shift w to nw and waves subside. To the n, a high swim risk will
develop for the Lake Superior beaches of Alger County this aftn as
brisk nw winds build waves.

Sfc high pres will build over the Upper Lakes tonight, leading to a
quiet/cool night. With precipitable water down toward 0.35 inches
for at least for the first half of the night, favored some of the
lower guidance for mins in the interior, especially w half where
winds will diminish quickest to light/calm during the evening.
Should see some frost in the interior w half as temps fall into the
mid 30s for at least the traditional cold spots.

.LONG TERM...(Monday through Saturday)
Issued at 329 AM EDT SUN SEP 17 2017

Overall, the upper-level pattern through the extended will start off
fairly progressive, but then will transition to more persistent
southwesterly flow through the end of the week and weekend as
ridging sets up across much of the eastern CONUS and longwave
troughing dominates the western CONUS. This will favor a brief cool
down through the early part of the week, but then the return of
above normal temperatures. There will be periodic chances for
showers and thunderstorms through the first half of the week, but
then as we transition towards the end of the week and through the
weekend, depending on where the baroclinic zone sets up
precipitation could become more prevalent at times.

Monday looks to be the coolest day of the week, with seasonable
temperatures expected as highs climb into the mid to upper 60s
across the area. As a weak shortwave lifts across the Upper Great
Lakes region, expect showers to push west to east across the area
late in the day and into the overnight hours. By Tuesday, longwave
troughing will continue to dig across the western CONUS with warm
air advection beginning to lift northeast across the region. As a
result, heights will rise throughout the day, giving way to a drier
weather, and temperatures will increase a few degrees compared to
Monday.

On Wednesday, a lobe of vorticity embedded within longwave troughing
will lift northeast across the Upper Mississippi Valley. This will
push a cold front across Upper Michigan Wednesday into Thursday,
bringing back chances for showers and thunderstorms. With mixed-
layer instability progged to increase to around 1000-1500 J/kg ahead
of the cold front, with the highest values expected to nose into
southern portions of Upper Michigan, there should be plenty of
potential for thunderstorm growth. In fact, with deep layer shear
increasing to at least 30 knots, a few storms may be on the strong
side. Coverage wise, the better forcing and moisture transport will
lift northeast of the area over Lake Superior, so convection across
the interior portions of Upper Michigan should be more scattered
than widespread. By Thursday morning, the cold front is expected to
slow its southward push and lift back north across the area by
Friday morning as return flow develops quickly ahead of
strengthening southwest flow aloft. This will favor a slight chance
for showers and perhaps a few rumbles of thunder as the front lifts
back north Thursday into Friday.

Friday through much of the weekend, we will remain in the warm
sector out ahead of another cold front progged to slowly push east
across Upper Michigan towards the end of the weekend. Temperatures
will push into the lower 80s in some locations as 850mb temperatures
climb back up to around 18 to 20C. There is some uncertainty in
regards to how precipitation chances will play out towards the end
of the work week and through the weekend, with the GFS being much
faster with the frontal passage than the Canadian and ECMWF. Given
the southwest flow aloft, tend to favor the slower progression with
the frontal boundary. Cannot rule out periodic chances for showers
and perhaps thunderstorms each day, but overall the best chance
looks to be towards the end of the weekend mainly out west.
&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 207 PM EDT SUN SEP 17 2017

Conditions continue to improve with just an hour or two of MVFR cigs
left at CMX and SAW. Expect VFR conditions with a few high clouds
through rest of the TAF period. WNW winds will gust over 25 kts at
CMX this aftn but should gust to 20 kts or less at the other TAF
sites.

&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 543 AM EDT SUN SEP 17 2017

With the passage of a cold front this morning into early aftn,
westerly winds will increase quickly to 20-30kt for much of Lake
Superior. Winds will then diminish to under 20kt from w to e tonight
as sfc high pres builds into the Upper Great Lakes. With high pres
lingering on Mon, winds should be mostly under 15kt. Winds should be
under 20kt on Tue, then stronger southerly winds of 20-25kt, even up
to 30kt over eastern Lake Superior, are possible on Wed as sfc trof
moves toward the Upper Lakes. Winds will drop off to under 20kt on
Thu.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Beach Hazards Statement until 9 PM EDT this evening for MIZ006.

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

$$

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



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