717
FXUS63 KMQT 221138
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
738 AM EDT Fri Aug 22 2025

.KEY MESSAGES...

- This evening, showers and thunderstorms push across the UP from
the west. A few may be strong to severe, with damaging winds being
the primary threat, resulting in a SPC Marginal Risk (category 1 of
5).

- A seasonably strong system moving north of the Great Lakes will
bring hazardous marine conditions to Lake Superior this weekend;
gales up to 35 knots are possible (30 to 40% chance).

- Cooler than normal temperatures and lake enhanced to lake effect
rain showers are projected to return this weekend.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 426 AM EDT Fri Aug 22 2025

This morning, RAP analysis shows the first shortwave associated with
a deep upper low over Manitoba passing near the northern shores of
Lake Superior. This shortwave is kicking off some thunderstorms over
the lake, though the highest concentration of lightning strikes and
highest reflectivities are staying over Canadian waters thus far.
Some rain showers are also shown on radar over the far western UP,
though no lightning has been seen with those showers yet. Showers
and storms are expected to wane in coverage and intensity this
morning as precip moves from a zone of high instability (SPC
Mesoanalysis MUCAPE of over 1000 J/kg over the western lake but
below 100 J/kg east of the Keweenaw Peninsula), though with various
CAM solutions showing isolated to scattered shower/thunder coverage
over the western UP, kept at least some PoP/Thunder mention in the
forecast this AM. A few METAR stations across the area are showing
visibility restrictions, though FG will only be patchy at most as by
the time RHs hit the high 90s to 100 percent range, winds will begin
picking up as surface troughing approaches. Expect low temps this
morning to be around 60.

A lull in the showers/storms is expected this late morning before a
more compact shortwave arrives over the UP this afternoon. Diurnal
heating will allow for significant destabilization to occur, which
in conjunction with supportive mid and upper level lapse rates, will
lead to HREF mean SBCAPE to climb to 1500+ J/kg over the west half
of the UP by 18Z, though mean 0-6km bulk shear of near 20 kt is
lacking, casting doubt on the ability of storms to properly
organize. Nonetheless, with lift, instability, and moisture (PWATs
near 1.5" is 90th percentile of NAEFS climo) in place, there is
enough of a ceiling of impacts that if some storms are able to
organize despite lacking shear, damaging wind gusts are possible (5-
14% chance per SPC Marginal Risk). Hail cannot be ruled out, though
dry air in an elevated HGZ casts further doubt on the chances for
severe hail (closer to 5 percent). The best window for the timing of
thunderstorms today appears to be 20Z-23Z in the west, 22Z-01Z in
the central, and 23Z-07Z in the east, though storms will not be as
strong in the east that late given instability from diurnal heating
will not be as present. While today may feel warm relative to the
past few days, highs in the upper 70s to near 80 is only a little
above average for this time of year (mid 70s). Skies then clear out
behind the storms, allowing for lows to fall to the mid 50s in the
interior west, with lows in the east and near the lakeshores being
closer to 60. With the strong upper low moving through northern
Ontario for Saturday, winds will begin to increase as brisk westerly
winds of 20-30 kt at around 900mb mix down to varying degrees across
the UP (most efficiently over the Keweenaw Peninsula).

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Issued at 345 PM EDT Thu Aug 21 2025

The long term period starts out fairly interesting as cold air
advection associated with a system moving from northern Ontario into
northern Quebec this weekend into early next week is projected to
bring early Fall-like conditions to the U.P. throughout the weekend
into next Monday. With 850mb temperatures progressively lowering
down to as low as 3C between Saturday morning and Sunday night,
given that the latest Lake Superior surface temperature analysis
from GLERL shows temperatures in the mid teens to around 20C, we can
expect lake enhanced rainfall to develop over the northwest wind
belts, eventually transitioning to pure lake effect rain by late
this weekend into early next week as delta Ts drop into the mid
teens. The increase in near-surface instability could make things
rather breezy for the Keweenaw on Saturday, with winds potentially
gusting above 30 mph throughout the day. With the European ensemble
highlighting the anomalously cold air aloft and low-level clouds
expected to develop from Lake Superior, expect the warmest
temperatures probably near the Great Lakes this weekend into early
next week; highs are expected to only get to mid 60s to lower 70s on
Saturday before plunging down to around 60 Sunday and Monday. As for
the lows, while the expected low-level cloud cover should help
insulate things, given the cold air advection getting into the area,
expect temperatures to progressively drop into the 40s through this
weekend to early next week; we may even see low even into the 30s by
Monday night/early Tuesday morning as the cloud cover clears out and
the lake effect rainfall ends.

While we should warm a bit closer to normal for middle to end of
next week, with high pressure blocking dominating the western half
of North America next week, we are expected to remain within the
influence of the cooler air brought about by a synoptic-scale low
that looks to set up shop by Hudson Bay/northern Quebec.
Nevertheless, we can expect highs to progressively rise from the 60s
into the lower 70s as we head into the end of the work week.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 738 AM EDT Fri Aug 22 2025

VFR conditions will be expected at all TAF sites today except for
some periods at IWD and CMX this morning in the wake of an early
round of -SHRA that is approaching SAW. This afternoon, a period of
TSRA is expected at all sites. There is a 5-14 percent chance that
those storms could produce damaging wind gusts and hail. Rain clears
out tonight and winds begin to shift from the southwest to the west
tonight into Saturday morning. There is about a 20% chance of some
overnight FG formation at SAW tonight, but some of that will be
dependent on how shower activity occurs earlier in the day, so will
leave out of the TAF for now, but future TAF issuances could
introduce periods of FG.

&&

.MARINE...
Issued at 345 PM EDT Thu Aug 21 2025

Fairly light and variable winds this afternoon give way to southwest
to westerly winds up to around 20 knots Friday over the western lake
between the Keweenaw and Isle Royale as a frontal boundary pushes
eastwards across the lake. This boundary could bring showers and
storms across the western lake tonight and is expected to bring
additional convection across the entire lake Friday and Friday
night, with some of the storms potentially bringing gusty, erratic
winds and small hail to the sfc.

As cold air advection behind a low pressure system moving eastwards
from northern Ontario to northern Quebec moves across the area this
weekend, expect the winds across Lake Superior to pick up, with west
to northwesterly gusts of 20 to 30 knots expected across the lake on
Saturday (highest along the northern shore of the Keweenaw); there
is even a 30 to 40% chance according to the LREF and NBM that gales
to 35 knots will be realized as well late Saturday afternoon. While
no gale products have been issued yet due to the probabilities being
too low at this time, we are continuing to monitor the situation as
it evolves; stay tuned to the marine forecast for the latest
details!

With cold air advection still cycling across the region the rest of
the weekend into early next week, west to northwesterly winds to 25
to 30 knots are still expected to continue across the lake, with
decreased chances of low-end (35 knots or so) gales still being
highlighted. However, as ridging builds back into the Upper Great
Lakes Monday night into Tuesday, expect the winds to begin dying
down once again, becoming 20 knots or less again late Monday night
and remaining that way until the middle of next week.

&&

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

&&

$$

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