Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 202023

Area Forecast Discussion
National Weather Service Marquette MI
423 PM EDT Thu Sep 20 2018

.SHORT TERM...(This evening through Friday)
Issued at 423 PM EDT THU SEP 20 2018

...Strong early fall storm with multiple hazards through Fri...

Deepening low pressure systems in the Upper Great Lakes in the fall
usually spell active weather. Next 24 hours is no exception with
mutliple hazards.

Large scale trough has shifted to northern Plains with primary sfc
low at 19z around 1000mb in northeast NE. Based on temps/dwpnts and
winds, sfc warm front stretches from low across northern IA and into
far southern WI/southern Lk MI and southern lower MI. Downright
steamy south of the front with lower 90s over lower 70s from
northern IA into northern IL. Meanwhile, Upper Michigan remains well
to the north of warm front stuck in stable low-level airmass with
stratus and expanding shield of light rain. Showers/t-storms btwn
these two distinct airmasses have been firing since this morning
over southern MN and based on latest high res models that are
initializing well, these t-storms are expected to lift from wcntrl
WI into western Upper Michigan by early this evening. Also still
watching for possible isold t-storms to develop farther east into
cntrl WI in the next few hours. Thus far think this is a low risk
since instability is nil in this area.

Thus far, all storms upstream in MN and WI are mostly rooted aloft
as they are firing on northern edge of MUCAPE gradient since the sfc
front is still well south of there. However, there still could be
risk of stronger wind gusts in stronger storms or even heavier
showers as the low-level jet overhead this evening is over 50 kts
from the SSW. At this point think bigger hazard will be heavy rain
with PWATS over 1.75 inches advecting into Upper Michigan on nose of
stronger H925-H7 moisture transport. At this point, think the system
remains progressive enough to keep flooding hazard mitigated. Issued
an SPS for western tier of Upper Michigan as don`t think a flash
flood watch is needed. Could see the need for an flood advisory once
radar trends are more evident so will be more of a nowcast issue.
Later this evening or early overnight, signal that line of t-storms
crosses west to east across Upper Michigan. Already seeing start of
a broken line of t-storms southeast SD into northeast NE. Certainly
a risk that these t-storms could be strong given the shear (0-1km
shear alone is over 50 kts and oriented perpendicular to expected
line) and overall strong dynamics/strong wind fields aloft. Best
expectation for arrival in western UP is 03z with exit east of Upper
Michigan around 09z. At the least should see brief heavy downpours
and gusty winds as this line moves through.

Attn late tonight turns to synoptic effects behind the exiting low
pressure system which slides east of Lk Superior on Fri morning. NW
winds 30-40 mph on Lake Superior will spread across all of northern
Upper Michigan by Fri aftn. Strongest wind gusts will be along Lk
Superior shore. Strong winds will result in building waves on Lk
Superior and have issued a lakeshore flood advisory for Marquette
through northern Luce county. Could need another lakeshore flood
advisory for tip of Keweenaw but will let mid shift decide on that.
Otherwise, day will feature falling temps and breezy conditions
across all of Upper Michigan. Lake effect rain showers expected with
sufficient mositure to H7 and sufficient instability as lake to top
of inversion delta t/s exceed 13c.

.LONG TERM...(Friday night through Thursday)
Issued at 336 PM EDT THU SEP 20 2018

After the late week shortwave slides east with a frontal boundary
following close behind, optimal radiational cooling conditions
develop Fri ngt across the Upper Peninsula. High pressure arrives
and should erode any lingering clouds with much cooler air aloft and
light winds. Current temperature guidance suggests temps could fall
into the lower 30s across the Central/Western portions of the Upper
Peninsula, and could easily see the traditional cold spots falling
into the upper 20s before daybreak Saturday.

The mid-lvl trough mainly stays north of the area; however, a
secondary frontal boundary is just north of Superior Saturday. This
could introduce additional clouds and a slight chance for showers.
The longwave pattern begins to flatten into a quasi-zonal
orientation, which may produce a day or two in the extended with
quiet weather. Although due to the faster mid-lvl flow the ability
for systems to easily traverse the Northern CONUS will bring small
chances for showers with temps in the 60s and cool overnights in the
30s to low 40s closer to Lake Superior and Michigan.

Tue/Wed of next week will start to focus on a system expected to
develop over the Central Rockies. This system will have much cooler
air sliding south from Canada mid-week, and will eventually arrive
across the Great Lakes. While we anticipate some moderation to the
airmass by late next week, guidance has been suggesting much colder
air to arrive for a brief period late next week.

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 143 PM EDT THU SEP 20 2018

Sticking with IFR conditions, with a chance for temporary LIFR,
through this forecast period. A low pressure system, and associated
warm and cold fronts, with ample moisture will make their way from
the Central Plains into Upper Michigan tonight. Patchy fog is
sticking around SAW this morning, and there are slight chances later
on for fog to redevelop after the first round of showers moves
through. Thunderstorm chances still remain for this evening into the
extreme early hours of Friday. If thunder does develop, expect
embedded thunder as the most likely scenario instead of discrete
thunderstorm cells. Confidence for thunder has increased some, but
will include as a vicinity for now as current high-res models have
not come to the same solutions for timing and coverage. Look for a
low-level jet with winds up to 60 kts to come in tonight which will
likely cause stronger wind shear for all TAF sites.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 423 PM EDT THU SEP 20 2018

Through tonight low pressure currently ejecting out of the central
Plains will track across Lake Superior into early Friday morning. As
the area of low pressure deepens, expect east gales up to 45 kts,
strongest over west half between Isle Royale and Duluth. As the low
pressure system exits east of Lake Superior on Friday, winds will
shift north-northwest and produce yet another round of gales across
all of Lake Superior. Peak winds could push 45 kts Fri aftn,
strongest over eastern Lake Superior. Friday night high pressure
will gradually slide eastward, reducing wind speeds across Lake
Superior. On Saturday, expect the winds to become southwest between
20 and 30 knots as a weak low pressure system tracks across Lake
Superior. On Sunday, winds will switch around and become northeast
around 20 to 25 knots. Expect southeast winds to 30 kts Mon into Tue
over Lake Superior, strongest over the east half.

Upper Michigan...
  Lakeshore Flood Advisory from 2 PM to 11 PM EDT Friday for

Lake Superior...
  Gale Warning from 8 PM this evening to 10 PM EDT Friday for

  Gale Warning until 6 PM EDT /5 PM CDT/ Friday for LSZ162-263.

  Gale Warning from 11 AM to 10 PM EDT Friday for LSZ250-251.

  Gale Warning from 11 AM to 8 PM EDT Friday for LSZ242>245-248-

Lake Michigan...
  Gale Warning from 11 PM this evening to 8 PM EDT Friday for



LONG TERM...Beachler
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