842
FXUS63 KMQT 311823
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
223 PM EDT Sun Aug 31 2025

.KEY MESSAGES...

- Isolated showers and or thunderstorms are possible this
  afternoon and Labor Day, mainly over the west half (15-30%
  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 to the Keweenaw.

- A cool airmass will build over the Upper Great Lakes late this week,
  providing the region below normal temperatures through the
  weekend.

- There is a 20-40% chance for northwest gales Tuesday night
  into Wednesday, mainly west and north of the Keweenaw
  Peninsula.

&&

.SHORT TERM /THROUGH MONDAY/...
Issued at 132 PM EDT Sun Aug 31 2025

High pressure over the area supported a mostly clear morning. This
allowed temperatures to warm into the low to mid 70s for most of the
region with light winds. Daytime heating is resulting in some
instability; this and a very weak wave aloft are supporting
scattered clouds over central and western Upper Michigan in the past
hour or two and more persistent broken to overcast skies far east.
As the afternoon progresses, a lake breeze off Superior may be the
focus for isolated or scattered shower or thunderstorm activity.
Vertical shear is very small or nonexistent, so anything that
develops isn`t expected to be strong or severe. Instead, these would
be expected to ride the lake breeze briefly or slowly diminish as
they move off the boundary.

Any convective activity should wane with the setting sun.
Afterwards, a mix of clear conditions and mid-high clouds are mostly
expected overnight. We should cool to near 50 interior and 50s or
near 60 lakeside. If rain does occur, cooling may support pockets of
fog where it rained. Monday, similar conditions are expected, with
the potential for afternoon showers and storms across the west with
daytime temperatures climbing into the 70s.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Issued at 223 PM EDT Sun Aug 31 2025

12z guidance continues to suggest mid-upper level ridging over the
region today will hold until at least Tuesday. At the surface,
1025mb surface high currently across the Great Lakes will edge
eastward Monday with waning 1020mb ridging extending westward across
the region into Tuesday. This ridge will weaken as a pronounced
upper level low is expected to dive southeast through Manitoba and
Ontario late Tuesday and Wednesday. Guidance over the past couple
hours has lead to some clarity in the potential evolution of the
event, namely to the question of a secondary low or not. Overall,
deterministic guidance is trending toward a surface low developing
over central Ontario Tuesday, which will help define/reinforce a
cold front pushing south. The upper level feature is then expected
to take on a negative tilt Tuesday night and Wednesday in response
to weak jet streak at 300mb, which will result in a secondary low
developing along the cold front Tuesday night/Wednesday morning over
western Lake Superior. This deepening surface low will gradually
lift northeast through the day Wednesday, then retrograde overnight
along the top of the upper level low in northern Ontario. The system
then gradually lifts northeast into James/Huron Bay Friday night and
Saturday. For Upper Michigan, confidence is high (>75%) that the
cold front and deepening low over Lake Superior will push a west to
east moving swath of light to moderate rainfall through the forecast
area Tuesday night and Wednesday. A tighter pressure gradient and
cold air advection are still present in deterministic guidance
packages, which suggests stronger winds will be possible,
particularly in the Keweenaw. But over the past 24hrs guidance has
presented a decreasing trend to the gradient force and less of a
temporal/spatial overlap of pressure rises and cold air advection
through the day Wednesday. This suggests slightly lower winds in the
Keweenaw then previously forecast; so instead of 30-40 mph winds,
guidance suggests 25-30 mph winds appear more likely.

Guidance has been consistent with the post frontal airmass though,
suggesting 850mb temperatures will eventually fall to +1 to -3C
Wednesday. In addition to the upper level low being over the region
into the weekend, the cooler temps atop the warmer lake will result
in scattered lake effect or lake enhanced rain pushing downwind into
Upper Michigan through at least early Saturday. A more organized
secondary cold front/trough may swing through Friday, which could
increase coverage of precip through the day. The airmass will also
yield daytime highs in the 40s and 50s Thursday, and 50s to low 60s
into the weekend thanks to weak warm air advection aloft. Overnight
lows in the 40s by the lakes and 30s interior are expected through
the weekend. Frost could be a concern Thursday night through
Saturday night; however, with the upper level low parked so close to
the region, resulting in continued cyclonic mid-level flow and
mostly cloudy skies, the potential for a secondary surface trough
Friday, and lake effect/enhanced rain, significant cooling may not be
achieved. The exception will be if there end up being breaks in the
clouds; at the moment though, this appears to be unlikely.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 132 PM EDT Sun Aug 31 2025

VFR conditions will prevail in this TAF period at all sites. A
shower or storm may pop up this afternoon and impact KIWD, but
confidence isn`t high enough to warrant a line in the TAF.

&&

.MARINE...
Issued at 223 PM EDT Sun Aug 31 2025

High pressure ridging over the region will, overall, result in winds
below 20kts for a majority of the period through Tuesday morning. By
afternoon on Tuesday, increasing pressure gradient ahead of the next
system will allow for increasing southwesterly winds across the
western and northern portions to build to near 20kts.

A cold front will then move move through the region late Tuesday
night into Wednesday. Overall, the forecast represents southwesterly
to southerly winds increasing 20-25kts ahead of the front (west late
Tuesday/Tuesday night and Wednesday east half) and then increasing
to near 30kts from the north-northwest to northwest behind the
front (Tuesday night and Wednesday).

Over the past 24 hours, deterministic guidance has gravitated toward
a secondary surface low developing along the front just northwest of
Thunder Bay or over western Lake Superior Tuesday night or early
Wednesday, then moving through northern Lake Superior before lifting
northwards through the day as the cold front pushes through the
Lake. While this doesn`t change the expectation of winds increasing
behind the front as they quickly become northwest, this progression
could delay the pressure rises building into the region behind the
front. Should this occur, the pressure rises and stronger cold air
advection may not align temporally or spatially, resulting in
slightly less wind speeds then previously forecast. This is
reflected in the decreased probability of gales suggested by most 0
and 6z ensemble guidance. However, some of this morning`s 12z
guidance appears to have ticked these probabilities higher,
similarly to what was suggested yesterday. This contrasts with these
system`s deterministic counterparts, which struggle to resolve gales
over the lake Wednesday in the 0-12z runs. With all this being said
though, all guidance packages continue to resolve the cold air
advection behind the front and suggest near 30kt winds in this
northwest to north-northwest flow. Guidance continues to suggest the
strongest winds will be positioned west of the Keweenaw between the
peninsula and Isle Royale with 25-30kts northeast and east of the
Keweenaw Peninsula. Northwest to westerly flow will persist over the
lake for the remainder of the week, slowly falling below 20kts by
late Friday. Its possible another cold front moving through our area
or a surface low to the south could support another round of near
30kt winds Friday, but confidence is currently low.

&&

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

&&

$$

SHORT TERM...JTP
LONG TERM...JTP
AVIATION...JTP
MARINE...JTP