447
FXUS63 KMQT 181138
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
738 AM EDT Fri Sep 18 2026

.KEY MESSAGES...

- Chance of rain (30-50%) mainly south of US-2 this evening through
Saturday evening. Chances of 1/3 inch of rain are less than 10% for
all except southern Menominee County.

- Low temperatures in the upper to mid 30s for the eastern UP and
isolated interior western UP locations will lead to a 20-40% chance
of frost formation. Those with sensitive outdoor vegetation should
keep an eye on the forecast.

- Dry pattern with high pressure sets up Saturday night through much
of next week. Fall-like temperatures in the early part of the week
trend warmer by the end of the week.

&&

.DISCUSSION...
Issued at 247 AM EDT Fri Sep 18 2026

Early morning GOES-East Nighttime Microphysics RGB imagery shows a
mixture of high clouds streaming in from the west associated with a
shortwave causing thunderstorms in Nebraska and South Dakota as well
as low stratus and at least some patches of FG (confirmed by METARs
reporting FG at SAW as well as others around the region). This
combination of cloud types should keep low temperatures from falling
out of the 40s this morning except for a few isolated typical cold
spots. Fog is not anticipated to become widespread.

The 500mb pattern consists of 599 dam ridging over Arkansas bounded
by deep troughs centered over the Pacific Northwest, the Bahamas,
and northern Quebec. The aforementioned ridge-riding shortwave
currently over western South Dakota will track a surface low south
of the UP this weekend and bring chances of rain to the southern UP
today and Saturday. The trend of rainfall southward continued in a
big way over the past 24 hours, with 00Z HREF showing
meaningful (15+%) probabilities of even a half a tenth of an
inch of rain by 00Z Sunday being limited to the immediate
vicinity of the state line and Menominee County south of US-2.
The 12Z LREF does at least shift some ~20% chances of measurable
rainfall a bit further into the UP, but impactful rainfall will
be certainly south of the UP as even the 90th percentile of the
LREF (reasonable worst case) is less than an inch even for the
Menominee area (and less than a third of an inch for all of the
UP except for Menominee County south of US-2). With the drying
trend in the forecast, especially with easterly flow descending
off the Canadian Shield, overnight lows into Saturday morning
look to be around the mid 30s in the interior east and in some
isolated locations of the interior west, which would lead to
frost potential (20-40% chance, especially for elevated
surfaces). Those in the eastern UP with sensitive vegetation
outdoors should monitor the forecast as the trend has been
colder, but if cloud cover from the southern disturbance extends
further north than currently forecast, temperatures may not
fall enough for frost formation.

In the wake of the disturbance, the western CONUS trough will shift
into the Northern Plains Sunday, weakening slightly. At the same
time, ridging to the north of the trough amplifies, causing split
flow. At this time, the favored solution is for the UP to be
affected by the northern branch of this split flow which will lead
to persistent high pressure and dry weather and near-normal to
slightly below normal temperatures for Sunday through at least the
first few days of next week until ensemble spread increases for the
midweek and beyond. The CPC 6-10 and 8-14 day outlooks both show
50+% chances for the UP to be in above average temperatures for the
end of September and a slight favoring of below normal precipitation
(30-40% chance).

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 737 AM EDT Fri Sep 18 2026

VFR will be the main flight category as TAF sites remain under the
influence of high pressure. Light winds continue through the
afternoon, shifting east as the day progresses. Low pressure passing
south of the region will bring increasing cloud cover and the
potential for showers at IWD. Confidence remains low in how far
north the showers will spread, so will continue to highlight
with PROB30s only at IWD.

&&

.MARINE...
Issued at 247 AM EDT Fri Sep 18 2026

Through Saturday, low pressure passing by to the south combined with
a high to the north will result in prolonged northeasterly flow into
the western arm of Lake Superior, with winds increasing locally to
20 kt and waves of 2-3 feet. A stronger high building to the north
on Sunday looks to expand coverage of 20-30 kt winds to most of Lake
Superior. Models disagree about gale potential, with the Euro
ensemble probabilities of gales now less than 10% while the NBM
projects gale chances of around 40%. Should the gale solution be
preferred, waves across Lake Superior (especially in the south and
the west) would build to 4-6 ft. Waves increase to near 3 feet over
northern Lake Michigan and Green Bay by Monday as well due to
prolonged easterly flow approaching 20 kt. For the beginning of next
week, high pressure building over Northern Ontario opposing low
pressure over the Lower Mississippi Valley will drive some gradient
wind gusts to around 20 kt out of the east before model spread and
forecast uncertainty increases late in the week.

&&

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

&&

$$

DISCUSSION...GS
AVIATION...TDUD
MARINE...GS