073
FXUS63 KMQT 011942
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
342 PM EDT Mon Sep 1 2025

.KEY MESSAGES...

- Isolated/scattered showers and or thunderstorms are possible this
Labor Day, mainly along the Lake Superior lake breeze (15-35%
chance).

- A cold front will move through the region Tuesday night and
Wednesday. This will bring widespread light to moderate rain to
Upper Michigan and breezy winds to the Keweenaw.

- A cool airmass will build over the Upper Great Lakes late this
week, providing the region below normal temperatures all the way
to the week`s end.

- There is up to a 30% chance for northwest gales Tuesday night into
Wednesday night, mainly west and north of the Keweenaw Peninsula.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 127 PM EDT Mon Sep 1 2025

GOES-East Visible imagery shows mostly clear skies over the UP, with
a couple of notable exceptions: Isle Royale, which has remnant cloud
cover from early morning convection and developing cumulus over the
central to western UP. Despite the 12Z CAMs backing off on
precipitation potential, a few showers and even thunderstorms have
kicked off in Marquette County already. There is some instability
aloft with the HREF showing a mean of around 500 J/kg, and a lake
breeze this afternoon will help further aid forcing. However, with
sub-10 kt flow up to around 500 mb, any showers that do get going
will lack the shear to maintain themselves for long, so severe
weather is not expected. With high pressure of around 1025 mb still
expanding across the Great Lakes basin, expect high temperatures to
climb to the mid 70s today. Once the evening clouds clear out, lows
tonight should be around the 50 degree mark in the interior and
around 60 for the lakeshores.

Throughout Tuesday, attention will be turned upstream as a deepening
negatively tilted 500mb trough pushes through the Canadian Prairie
and approaches the UP. The resulting low pressure of around 1008mb
will be around Thunder Bay by 00Z Wednesday per the GEFS. Prefrontal
showers are expected to arrive in the west half of the UP through
the afternoon, though they will be disorganized showers as the shear
will not notably improve until after 00Z when the surface low and
compressed flow nearer the trough axis aloft passes near the UP. A
few of those showers could be efficient rainmakers as 75th
percentile of 6-hour QPF rates in the LREF show up to a quarter of
an inch of rain in the stronger portions of the showers. Otherwise,
expect a very similar high temperature forecast to today with highs
around the mid 70s.

&&

.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
Issued at 342 PM EDT Mon Sep 1 2025

Tuesday night through Thursday morning, the trough axis will sweep
over Lake Superior. While the surface low is expected to stay to the
north of the UP, the attendant cold front will march across the area
Wednesday, bringing with it widespread rainfall and a few
thunderstorms. The post-frontal winds will be worth watching
especially for interests on Lake Superior or near the lakeshores as
rapid height falls along with rapid pressure falls is generally a
good setup for winds to overperform model guidance, and the LREF
already has chances of gales around 20-40 percent. This forecast
will reflect sub-gale conditions in line with the NBM, though would
not be surprised if this climbed up more as more medium-range
guidance begins to model this regime.

The cool northwesterly flow and lowered heights behind the cold
front will lead to cool temperatures both at the surface (NBM
*highs* Thursday in the upper 40s in interior Marquette County) and
aloft, with the LREF showing 90+% chances of prolonged temperatures
below 3 C, which when compared to Lake Superior`s temperature being
around 16 C, leads to unstable enough conditions for lake enhanced
to lake effect precipitation. As the LREF still shows no surface
temperatures sub-freezing yet, this will fall as light rain.

A secondary trough will drop down from the Canadian Prairie into the
Midwest Friday through the weekend, eventually merging with the
aforementioned trough which will continue to wobble around northern
Ontario. This will bring another surge of yet-cooler temperatures,
with Sunday morning being the coolest morning of the forecast as NBM
lows fall into the mid-30s for the interior west. Should some breaks
in the lake-effect/enhanced precip and clouds occur, some frost is
possible, but with the uncertainty around the potentially
insulating cloud cover, will elect to keep just mentions of
patches of frost at this time. This trough will also bring
chances of gusty northwesterly winds potentially up to gale
force (20% chance late Friday) and rain (lake enhanced and lake
effect). Following the trough merger, troughing advances towards
eastern Canada and the UP finds itself upstream of central
North American longwave ridging, and the resulting surface high
pressure eventually brings an end to precipitation and slightly
warmer temperatures by the late weekend/early next week
timeframe.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 127 PM EDT Mon Sep 1 2025

Generally VFR conditions dominate the TAF sites today and tonight.
However, some diurnally induced showers and storms could impact the
TAF sites this afternoon, although chances are 20% or less despite
SHRA and TSRA in the northwest VC of SAW this early afternoon.
Expect the light winds today to turn to the southwest tonight as a
cold front approaches from Canada. This cold front will bring rain
showers and potentially TSRA to at least IWD by 12-18Z Tuesday, if
not also CMX, with SAW staying dry until after 00Z Wednesday. SAW
also carries a 15 percent chance of overnight FG formation tonight
but confidence is too low to include in the TAF at this time.

&&

.MARINE...
Issued at 342 PM EDT Mon Sep 1 2025

High pressure over the Great Lakes will result in winds below 20kts
through Tuesday. Overnight into Wednesday, increasing pressure
gradient ahead of the next system will allow for increasing
southwesterly gusts across the eastern end of the lake to build up
to 20-25kts.

A cold front will then move move through the region late Tuesday
night into Wednesday. Overall, the forecast represents southwesterly
to southerly winds to 20 kts ahead of the front and then increasing
to 25 to 30kts from the north-northwest to northwest behind the
front (Tuesday night and Wednesday). Differences in the exact setup
of the system continue to reduce confidence in gales, though this is
a setup that tends to outperform guidance. Currently chances of
gales are about 15-30 percent, though some guidance suggests higher
chances (up to 50 percent) of a localized gale in the Isle Royale
vicinity Wednesday night. This front will also bring with it 30-40
percent chances of thunderstorms and the gusty winds behind the
front will bring waves up to 6 ft.

For the late week period, as the main trough remains broadly over
northern Ontario, winds shifting to the west and southwest remain
around 20 kt, perhaps falling below 20 kt late Thursday into early
Friday. A secondary trough will merge with the first Friday into the
weekend, reinvigorating wind gusts into the 20s kt range with
another around 20 percent chance of gales Friday night. Northwest
winds remain gusty and waves increase to 5-7 ft Saturday before the
gusts fall below 20 kt by Sunday as the disturbance lifts out of the
area and high pressure establishes itself to end the weekend and
begin next week.

&&

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

&&

$$

SHORT TERM...GS
LONG TERM...GS
AVIATION...GS
MARINE...GS