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