National Weather Service Raw Text Product

768 
FXUS63 KMQT 202321
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
721 PM EDT Wed Aug 20 2025

.KEY MESSAGES...

- Patchy, locally dense fog returns tonight into Thursday morning.

- Dry weather is expected through Thursday before the next
  chances of showers and thunderstorms return to the UP Friday
  evening. There is currently a Marginal Risk (level 1 of 5) for
  severe weather.

- A seasonably strong system moving north of the Great Lakes
  will bring hazardous marine conditions to Lake Superior this
  weekend.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 326 PM EDT Wed Aug 20 2025

GOES satellite reveals mostly cloudy skies overhead slowly clearing 
as high pressure inching southward across Lake Superior ushers in a 
drier airmass aloft. So far today, fog and drizzle have clung to the 
central UP amidst light, moist upsloping, though the drizzle is 
finally starting to taper off. Temps have managed to climb to the 
mid to upper 60s save for the far east where breaks in the clouds 
have provided enough sunshine for some low 70s. Tonight, skies 
continue to clear while low level moisture hangs around, creating 
the ideal setup for radiational fog. 12z HREF paints a 60-90% chance 
for visibility less than 1 SM from roughly 3-9 AM EDT across the 
northern tier of the UP, particularly area affected by northerly 
upsloping. Probability for dense fog decreases to the south, but 
conceptually I would not be surprised to see widespread fog in the 
early morning hours across much of the interior south and west. 
Otherwise, low temps will fall into the 50s. Once the fog breaks 
Thursday morning, expect mostly sunny skies and light winds through 
the day with afternoon temps pushing into the mid 70s to near 80.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
Issued at 326 PM EDT Wed Aug 20 2025

After a quiet Thursday, a seasonably deep trough is forecast to dive 
southeast across Sask/Manitoba into the northern Great Lakes this 
weekend. The first round of associated weather impacts comes in the 
form of a cold front set to move west to east into Upper Michigan 
sometime Friday evening into early Saturday morning. A few strong 
thunderstorms may accompany the frontal boundary given 
afternoon/evening MUCAPE values pushing 1000 j/kg (potentially 
higher given your choice of model), though weak upper level lapse 
rates and bulk shear <30 kts may limit severe potential. For these 
reasons, SPC has included much of Upper Michigan in a Day 3 Marginal 
Risk (level 1 of 5) for severe weather.

The subjectively more interesting and potentially just as impactful 
weather follows the cold frontal passage into this weekend and early 
next week. By Saturday, deterministic models are in decent agreement 
that the deep closed upper low and associated sfc pressure 
reflection will be placed solidly atop north-central Ontario, 
however, they begin to diverge into Sunday, with the GFS suite 
conjuring a stronger secondary trough diving into the N Plains and 
western Lakes into Monday. Meanwhile, the Euro/Canadian members 
maintain the closed low spinning stop James Bay through Monday 
before pushing northeast into Quebec. Regardless, stout NW flow 
aloft into the late weekend will send fall-like 850mb temps crashing 
into the single digits (10th to 2.5th percentile via NAEFS 
climatology). 00z LREF suggests a 30-50% chance for 850 temps <5C 
across northern Lake Superior by Sunday evening, increasing >70% by 
Mon/Tues. With the average Lake Superior temperature around 17-18C 
(near the climatological summertime peak), the incoming cool airmass 
will support efficient momentum transfer as well as drive lake 
effect/enhanced clouds and precipitation outside of showers driven 
by embedded shortwaves pinwheeling around the deep upper low.

The big question is whether or not we can achieve the Gales of 
August on Lake Superior this weekend. Ensembles are hit or miss, 
with the ENS suggesting a <40% chance in the western lake and 
Keweenaw along the initial push of CAA Saturday night into Sunday. 
However, NBM 24hr max gust >34 kts depicts a broad 50-70% chance in 
the open waters west of the Keweenaw followed by 30-50% chances both 
east and west of the Keweenaw through Sunday. Probability for gusts 
>22 kts are nearly 100% across the entire lake through the weekend.

With the cooler airmass overhead, expect fall like temps in the 60s 
Sunday into the coming week and overnight lows in the 40s and 50s. 
NBM 25th percentile points towards what could be our first frost 
headline Monday/Tuesday night, though this will be contingent on 
cloud cover and wind. Tuesday night looks to be a better shot with a 
slackened pressure gradient across the region as high pressure 
expands across the Plains.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 721 PM EDT Wed Aug 20 2025

Light northerly to light and variable winds overnight under high 
pressure and moist low levels will support fog/mist developing 
overnight. This is likely to bring IFR and LIFR conditions to all 
airports, particularly though at KSAW which may fall below airport 
minimums. Latest HREF suggests near 70% chance of 0.25 miles 
visibilities or less tonight. Conditions should begin to improve 
Thursday with the sunrise, with VFR conditions expected to prevail 
thereafter.

&&

.MARINE...
Issued at 326 PM EDT Wed Aug 20 2025

Light and variable winds less than 15 kts continue today 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 becoming more 
likely, though uncertainty still remains high. Ensemble model 
guidance are hit or miss, with the ENS suggesting a <40% chance in 
the western lake and Keweenaw along the initial push of CAA Saturday 
night into Sunday. However, NBM 24hr max gust >34 kts depicts a 
broad 50-70% chance in the open waters west of the Keweenaw followed 
by 30-50% chances both east and west of the Keweenaw through Sunday. 
Probability for gusts >22 kts are nearly 100% across the entire lake 
through the weekend.

&&

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

&&

$$

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