349
FXUS63 KMQT 200701
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
301 AM EDT Wed Aug 20 2025

.KEY MESSAGES...

- Patchy, locally dense fog forms by the end of the morning,
clearing out for the daytime, then returning tonight into Thursday
morning.

- Dry weather expected through Thursday before the next chances of
showers and thunderstorms return to the UP Friday.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 259 AM EDT Wed Aug 20 2025

GOES-East Nighttime Microphysics RGB imagery once again shows a
widespread collection of cool low-level cloud cover over the UP
early this morning. METAR observations confirm overcast conditions
at many locations, though observations like CMX show that there
are some breaks in the cloud coverage. Despite the abundant
remnant low level moisture and upsloping flow from Lake
Superior, little to no fog has formed as of 06Z, though at least
some patchy fog is forecast by the end of the morning (HREF
probability of sub-1 mile visibility is 40-80 percent along the
terrain following the Lake Superior shores). Given temperatures
already at or near their dew points, not expecting low
temperatures this morning to fall much below the 60 degree mark
for most. Despite some CAMs showing embedded light rain with
this moisture, METAR and radar observations lack support for
this, so went with a dry forecast.

RAP analysis shows large-scale ridging aloft over much of the Plains
and Prairie of central North America, which is translating to broad
high pressure near 1020mb over much of the Midwest. This high
pressure will eventually shift to be fully over the Great Lakes
basin today, and the subsidence from that should allow for a gradual
clearing of skies through this afternoon with mostly clear
skies overnight tonight. Clearing will be a bit too late for the
most efficient radiational warming, which in conjunction with
the cool northwesterly flow aloft, will keep high temperatures
only around the 70 degree mark today.

With the clearing skies, despite a slightly drier airmass being over
the area, at least some patches of fog are expected to return as
radiational cooling with light winds under the high pressure is a
prime setup for fog formation. This is also supported by the HREF
which models 40-70% chances of widespread visibilities under 1 mile
tonight. Low temperatures will fall close to the dew point, which
should be near the mid-50s.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
Issued at 254 PM EDT Tue Aug 19 2025

By 00z Thursday, ~1020mb sfc high pressure will be placed solidly
atop Lake Superior as a digging trough in the Canadian Rockies and
stout upper ridge over the Four Corners amplify heights over the
central CONUS. With this, quiet weather and a brief warm up is
expected Thursday and Friday. 850 temps reaching 13-15C will allow
daytime temps under sunny skies to climb near the 80 degree mark.
The next chance for precipitation across the Upper Peninsula arrives
sometime Friday evening as the aforementioned Canadian Rockies
trough swings southeast into western Ontario by 00z Saturday,
sending a cold front across the region that may kick off showers and
thunderstorms. Behind the cold frontal passage, modest cold air
advection aloft spills across Lake Superior. 850 temps fall below
10C Saturday and even further towards 5C by the end of the weekend
into early next week. With average lake temps near 17-18C, would not
be surprised to see some lake effect/enhanced clouds or precip as
multiple passing shortwaves embedded within the adjacent closed
low press through the Upper Great Lakes this weekend.
Additionally, gusty W to NW winds and cooler temps aloft will
bring in cooler daytime temps in the 60s to upper 50s
Sunday/Monday with overnight lows in the 40s away from the
lakeshores.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 100 AM EDT Wed Aug 20 2025

Ceiling and visibility restrictions to persist at all TAF sites
through this morning as moist northerly flow continues to support
fog and low clouds. Currently, VFR has briefly returned to CMX, but
anticipate that site to deteriorate to LIFR again in the Wed 06-09Z
time frame along with both IWD and SAW. IWD could see a return to
MVFR by mid-morning, but not much improvement is expected at CMX
or SAW.

&&

.MARINE...
Issued at 133 PM EDT Tue Aug 19 2025

Light winds becoming northerly by tonight will hold below 20 kts
through tonight. Patchy fog is expected over much of the lake during
this period, becoming dense at times to 1 mi or less into Wednesday
morning. A Dense Fog Advisory has been hoisted for much of the
central lake through this evening, but extending and expanding of
the advisory is anticipated to capture increasing visibility
deterioration into Wednesday.

Variable winds less than 15 kts are expected for Wednesday and much
of Thursday as high pressure builds overhead. Southerly winds
increase Thursday night as troughing develops to the west, becoming
southwest up to 20 kts for Friday as high pressure shifts to the
Lower Great Lakes. A low pressure system then tracks over northern
Ontario this weekend, sending a cold front across the lake Friday
into Saturday and reintroducing west becoming northwest winds into
the 20-30 kt range for Saturday and Sunday as a seasonably cold
airmass settles in. Significant wave heights are expected to
increase to 4-6 ft as a result of persistent winds. Gales to 34 kts
are currently unlikely (<15% chance), but will continue to monitor
this period.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
  Dense Fog Advisory until 4 AM EDT early this morning for
     LSZ263-264-266.

Lake Michigan...
None.

&&

$$

SHORT TERM...GS
LONG TERM...BW
AVIATION...TDUD
MARINE...Jablonski