195
FXUS63 KMQT 011727
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
127 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 TONIGHT/...
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 THROUGH SUNDAY/...
Issued at 344 AM EDT Mon Sep 1 2025

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 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 344 AM EDT Mon Sep 1 2025

High pressure ridging over the region will 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 up to 20kts.

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 (west late
Tuesday/Tuesday night and Wednesday east half) and then increasing
to 25 to 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 up to 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.
increasing 20-25kts

&&

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

&&

$$

SHORT TERM...GS
LONG TERM...JTP/TAP
AVIATION...GS
MARINE...JTP/TAP