430
FXUS63 KMQT 161501
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
1101 AM EDT Sat Aug 16 2025

.KEY MESSAGES...

- Afternoon showers and thunderstorms, some strong-to-severe,
present a Marginal Risk for damaging winds (category 1 of 5) and
excessive rainfall (category 1 of 4).

&&

.UPDATE...
Issued at 1101 AM EDT Sat Aug 16 2025

The remnants of the MCS that made its way through Minnesota
overnight are showing an interesting evolution over western WI this
morning. A more active portion is diving southward into central WI
with lightning picking up once again. Meanwhile, the leading edge of
a comparatively weaker swath of storms is heading northward into NW
WI, towards the UP and the western arm of Superior. This is a less-
than-favorable area for stronger convection, with a more stable
airmass north of the NE-SW oriented frontal boundary that is already
sinking into the UP. Still, upwards of 40kts of deep-layer shear is
analyzed over the area, and the line appears to be bowing out with
some higher velocities apparent from the DLH radar. So, will not
rule out some gusty winds with this as it begins to move into the
western UP over the next hour. Behind the leading edge? A large
swath of stratiform rain and embedded thunder.

Meanwhile, upper level cloud cover continues to fill in from west to
east across the UP. It remains to be seen what kind of impact this
will have going forward; will this inhibit further destabilization
over the eastern UP? The thinking so far has been that the frontal
boundary and approaching wave would be the focus for some
potentially stronger daytime convection featuring embedded heavy
rainfall rates. However, if convection currently off to the west
cannot keep it together, and if cloud cover reduces instability out
eastward, we may end up with mainly a stratiform rain/embedded
thunder scenario. This could still feature some embedded moderate to
heavy rainfall rates at times. The forecast has been updated to
reflect latest radar trends.

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 501 AM EDT Sat Aug 16 2025

Upper air pattern consists of an expansive upper high over the Lower
Mississippi Valley and a deep cutoff low over Hudson Bay, with
ridging also being seen over the Canadian Rockies. This translates
to expansive 1020mb high pressure over much of the eastern CONUS,
low 1020s mb high pressure over Manitoba, and a 996mb low over
Hudson Bay. The cold front draped south of the low is somewhat
diffuse but is broadly over the region this morning, and enough
forcing has been present to initiate a few isolated short-lived
thundershowers in the west earlier in this overnight period and some
scattered thunderstorms in the eastern UP. While the lightning will
provide some hazard to campers at Pictured Rocks National Lakeshore
and Lake Muskallonge State Park, storms have remained comfortably
sub-severe so far. While storms have had some elevated CAPE to work
with (MUCAPE up to 1000 J/kg), effective bulk shear values sub-25 kt
has kept storms disorganized and limited the severe potential for
these thunderstorms. The sub-severe nature of the storms will
continue through the morning hours as storms move into a less
favorable CAPE environment with meager shear expected to continue
through the morning.

A particularly subtle shortwave will be the focus of thunderstorms
across the Upper Midwest. Due to the sub-synoptic scale of such a
feature, there is still some spread as to the details of the timing
and placement of showers and thunderstorms as they pass through
MN/WI and approach or pass through the UP/Upper Great Lakes. The
HRRR consistently puts out the worst case scenario for the UP: a
solid to broken line of strong to severe storms transiting the UP
starting in the west around 17Z and ending in the east around 00Z.
However, it is worth noting most of the other CAMs show only
scattered to isolated cells with most of the MCS-like features
staying south in WI. Conditional on the presence of storms, the best
instability will be in the south-central to eastern Lake Michigan
shores with HREF mean SBCAPE values this afternoon to evening up to
1500 J/kg. Better shear will move over the UP in the afternoon to
evening hours as well, with 0-6km shear climbing to 30+ kt and 0-3km
SRH values climbing above 100 m2/s2. Moisture continues to be
bountiful as NAEFS PWATs predicted upwards of 1.75 inches are in the
99th percentile for this time of year. Chances of a wetting rainfall
(generally a tenth of an inch or more) are in excess of 60-80%
widespread across the UP (except Keweenaw County with lower
probabilities), though PMM precip charts show the potential for up
to 2+ inches in the worst-case scenario that multiple cells train
over a location or if a line sets up parallel to storm motion. On
the excessive rainfall and severe weather potential, the WPC and SPC
respectively have issued Marginal Risks as just the right forcing in
the right time could be impactful, though uncertainty remains high.

As the south and eastern UP stays in the warmer sector of the
diffuse surface trough longer, high temperatures especially along
Lake Michigan will be around the 80 degree mark today, with the
northern and western UP struggling to break into the 70s (especially
if cloud cover from upstream convection blocks out the sun). As high
pressure sets in overnight tonight, expect clearing skies to allow
temperatures to fall to the 50s and low 60s. A near 30 kt 900mb jet
will create some gusty conditions especially along Lake Superior
tonight into Sunday, which will increase the wave heights and create
some potentially hazardous small craft and swimming conditions. PoPs
creep back into the forecast along the MI/WI state line Sunday PM as
a more pronounced shortwave trough ejects out of the high plains and
approaches the Upper Midwest, though the bulk of that precipitation
will fall during the early portions of the work week.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Issued at 501 AM EDT Sat Aug 16 2025

A shortwave moving through the Northern Plains approaches the Great
Lakes Sunday night into Monday, but looks to weaken slightly as it
encounters persistent eastern CONUS ridging. Still, with weak WAA
and weak forcing courtesy of the shortwave, chances for showers and
storms trend upwards for the UP Monday, wrapping up sometime Monday
night into Tuesday. Will note that differences persist among model
suites regarding the strength and timing of this next wave, and thus
the location and timing of any convection. After Tuesday, guidance
favors a period of ridging into the middle of the week with dry and
quiet weather persisting at least until Friday. Then, another
shortwave looks to drop through. Otherwise, it does look like
temperatures, after climbing above normal today, will trend toward
normal to slightly below normal as we head into the middle of next
week. After that, a warming trend is expected midweek onwards.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 739 AM EDT Sat Aug 16 2025

Low-end MVFR at SAW and IWD will improve to join CMX at VFR later
this morning. -SHRA and TSRA will then impact IWD and SAW beginning
late this morning and lasting into tonight, with CMX about 30
percent likely to see SHRA and about 20 percent likely to see TSRA.
Some of the afternoon -TSRA could bring gusty and variable winds,
potentially severe. With the precip will come some MVFR conditions
to potentially IFR (20% chance). As high pressure fills in behind
the precip tonight, all sites return to VFR conditions.

&&

.MARINE...
Issued at 348 PM EDT Fri Aug 15 2025

South-southwest winds continue to gust to around 20kts mainly
between the Keweenaw and Thunder Bay this evening, though some ~20kt
gusts are also possible in the far eastern portions of Lake Superior
through this evening. Winds gradually fall back after sunset.
Meanwhile, some showers and storms are working into the western arm
of the lake, and may continue to push eastward across the lake the
rest of this evening. An approaching cold front will bring a chance
for additional spotty showers/storms later tonight while shifting
winds first to the north and then northeast into Saturday. Winds
across the western arm of the lake increase to around 20kts Saturday
afternoon. 20-25kt gusts become common across the entire lake
Saturday night through Sunday. Higher gusts around and in excess of
30 knots are possible over the western half of the lake; as of the
time of this writing, ensembles show a 20-30% chance for gale force
gusts up to 35 knots being seen over the western arm Sunday
afternoon and evening. Winds slacken slightly into early next week;
nevertheless, some easterly winds of 20 to 25 knots could still be
seen across the lake Monday, in addition to showers and
thunderstorms. Winds lighten to 20 knots or less and more stable
conditions return by the middle of next week as high pressure
ridging from Canada comes back to the region.

&&

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

&&

$$

UPDATE...LC
SHORT TERM...GS
LONG TERM...GS/LC
AVIATION...GS
MARINE...LC