Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 182336

Area Forecast Discussion
National Weather Service Marquette MI
736 PM EDT Tue Sep 18 2018

.SHORT TERM...(This evening through Wednesday)
Issued at 358 PM EDT TUE SEP 18 2018

Cool start to the day compared to our recent weeks` warmth. Low-
level stratus have kept temperatures down well in to the 50s across
the CWA. Early morning drizzle occurred in the Central U.P., but the
lower clouds have stuck around throughout the day. Upper level winds
have been on the low side today helping these clouds stick around.
Current model trends want to clear some of the clouds tonight,
especially north, however, confidence is quite low with amount of
clouds seen on visible imagery. With stratus projected through most
of the night, low temps were brought up a few degrees compared to
recent forecasts. If clouds clear some, expect temperatures to drop
a few more degrees than the forecast.

For tomorrow, clouds should linger around much of the day ahead of
our next weather system coming in the early hours of Thursday. Toned
back temperatures for tomorrow to a few degrees warmer than
persistence. The Euro and GFS have conflicting ideas for
temperatures tomorrow with some of the bigger differences being the
temperatures across the central U.P. There will be slight WAA
tomorrow afternoon across the U.P., but timing and intensity is
still a little different between the two models as well. Therefore,
going a little warmer tomorrow than today with highs around 60
across the CWA. Chances for precipitation will increase throughout
the day on Wednesday, but not expecting anything widespread until
Thursday when the better dynamic forcing and surface low make their
way into Upper Michigan.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 429 PM EDT TUE SEP 18 2018

...Another heavy rain event to impact portions of Upper MI...

Ridging/significant positive 500mb height anomalies extending from
the Aleutians toward the North Pole are still expected to migrate e
over the next 7-10 days with the main anomaly reaching the Gulf of
Alaska by the middle of next week and perhaps British Columbia by
the end of the week. This will support continued troffing vcnty of
the Canadian coast/Pacific NW thru the weekend before the
progressing ridge shifts troffing downstream to central N America.
Meanwhile, central CONUS to se Canada ridging which brought the
extended period of late summer/early fall warmth to Upper MI has
been suppressed by shortwave energy tracking from the southern
Canadian Rockies to se Canada. Combination of a deep mid-level low
dropping from the Canadian Arctic to Hudson Bay this week and
shortwave trof shifting across the northern CONUS will then work to
prevent resurgence of ridging back into the area. As a result, temps
thru early next week will not stray too far from typical mid to late
Sept readings, though it could be quite chilly on Fri. As for pcpn,
main pcpn event this week will be tied to shortwave currently
approaching the W Coast. As it swings e, reaching the Upper Lakes
late week, mdt to hvy rainfall will occur here Thu/Thu evening. A
trend to dry weather will follow later Fri into Sat. A cold front
will then drop across the area Sat night/Sun, providing a chc of
shra. Yesterday, it appeared low amplitude flow would prevail early
next week, but models have trended toward trof amplification into
the western CONUS ahead of the aforementioned ridge shifting e from
the Aleutians. Progression of this trof downstream could spell
another mdt to possibly hvy rain event toward the middle of next
week in the Upper Mississippi Valley vcnty.

Wed night thru Thu night...shortwave trof moving across the western
CONUS Wed will reach the Plains Thu and the Upper Lakes by Fri aftn.
In response, low-level jet will begin to increase across the Plains
Wed night and will then aim into the Upper Lakes Thu aftn/evening as
it strengthens to 60kt. Initially, Wed night, warm front to the s
across WI may hang up with weak lead shortwave aiding convection
vcnty of the front. Many of the models sharpen the frontal
boundary/veer 850mb winds s of the boundary due to the convection,
and this holds up its northward movement. That`s not unreasonable,
especially given multi-model solution. As a result, should just see
sct lighter shra spread across much of the area Wed night. Heading
thru Thu/Thu night, the last 24hrs of model runs have shifted low
track westward with agreement quite good now for a deepening low
tracking from eastern CO Wed evening across far western Upper MI Thu
evening. This will shift heaviest rain corridor to nw WI/far western
Upper MI and western Lake Superior. As nose of strengthening low-
level jet shifts toward the Upper Lakes, warm front will steadily
lift n on Thu, and with expected low track across far western Upper
MI, the front will likely clear much of the fcst area. With abundant
moisture in an absolute sense having never been cleared out of the
central CONUS (widespread 1.5in or higher precipitable water values
per 12z soundings currently cover much of the Mississippi
Valley/eastern Plains) and with deep flow off the western Gulf of
Mexico ahead of the approaching trof, NAM/GFS show precipitable
water surging to around 2 inches Thu aftn/evening, again nearing
record territory for Sept. Very strong moisture transport, anomalous
precipitable water and high freezing levels (12-13kft) to increase
warm rain processes support a hvy rain event. Track of sfc low, best
overlap of strong 700 and 850mb moisture transport and most
persistent fgen suggest far western Upper MI will see heaviest
rainfall totals. Shifting axis of strong moisture transport will
support hvy rainfall eastward, but it should be more transient than
over the far w. Likely looking at widespread rainfall amounts of 1-2
inches, lowest e, with 2-3, locally 4 inch totals possible far w. If
sufficient instability builds ne into Upper MI e of the low track,
deep layer of shear of 45+kt will support a risk of svr storms into
central Upper MI in the evening along/ahead of cold front. There
will proabably be considerable cloud cover, so right now
it appears instability build up will likely be hindered.

Mdt/hvy rainfall will wind down Thu night, but cyclonic flow and
850mb temps falling toward 0C will result in lingering -shra which
will take on a lake component as air mass cools under nw to nnw low-
level flow. These -shra will end w to e Fri aftn into early Fri
evening. Will be a chilly, blustery day Fri, typical of passing fall
storm systems. Fairly strong CAA and favorable orientation of
incoming pres rises will aid gustiness. Expect gusts 20-30mph with
locations exposed to nw-nnw winds along Lake Superior likely gusting
to 35 to as much as 40 mph for a time. Aftn temps will probably only
be around 50F w and n central.

Passing sfc high pres and drying column Fri night will set the stage
for a chilly night. Leaned forecast toward the lower side of
guidance. Will probably see a widespread frost across the interior
of w and central Upper MI provided clouds clear out.

Sat looks dry at this point as sfc high pres departs, and then there
may be a few -shra Sat night/Sun as a cold front drops into the

Models have shown poor run-to-run consistency for early next week,
but trends suggest an amplifying trof into the western CONUS early
in the week which will shift to the central CONUS by midweek.
Another healthy surge of moisture n ahead of this trof will likely
produce another mdt to potentially hvy rain event. Right now, it
appears associated sfc low will probably lift ne to the w of Upper
MI, so heaviest rainfall should pass w of here with this system.
Given inconsistencies, mainly chc pops were utilized, arriving Mon

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 729 PM EDT TUE SEP 18 2018

Stratus persists across the area impacting KIWD and KCMX with
MVFR conditions and KSAW with IFR conditions. Models indicate some
slow improvement into Wednesday as winds shift from ne to e, but
still MVFR conditions are expected. &&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 358 PM EDT TUE SEP 18 2018

Overall, we moving into the fall time pattern, with higher winds
expected over the next week. Winds will remain around 10 knots from
the N, veering to E early Wednesday morning. Waves should also
remain around 2 feet throughout the evening. Wind and waves will
increase late Wed into Thur as a surface low begins to move into the
U.P. Gale force conditions are becoming more likely Thursday evening
over Western Lake Superior, and moving to more Central and Eastern
Lake Superior Thursday overnight into Friday morning as the low
pressure system moves East into Canada.

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


LONG TERM...Rolfson
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