221 FXUS63 KMQT 190017 AFDMQTArea Forecast Discussion National Weather Service Marquette MI 817 PM EDT Thu Sep 18 2025
.KEY MESSAGES...
- Isolated to scattered showers and thunderstorms possible tonight and Friday across western Upper Michigan.
- Seasonable temperatures through the weekend.
- Rain and thunderstorms chances exist through early next week.
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.DISCUSSION... Issued at 223 PM EDT Thu Sep 18 2025
Early afternoon GOES satellite imagery reveal a closed upper low placed atop the northern Plains with a few embedded shortwave wobbles within the broad low. This is reflecting a ~1014 mb sfc low pressure in eastern SD. Closer to home, the northern Great Lakes sit under the western flank of an expansive ridge with sfc high pressure nosing southward from the Hudson Bay down into Lake Superior. Weak synoptic forcing has managed to kick off a few light showers across the western UP and WI/UP border counties, though subsidence has kept this precipitation confined to these areas and showers have largely died out with and further eastern attempt.
Tonight, expecting similar conditions with mostly cloudy skies though there may be an uptick in spotty shower activity in the far western UP as one of the aforementioned embedded waves rotates around the parent upper low and lifts into western WI by Friday morning. Scattered spotty showers linger across the west through Friday. Breezy east winds will keep temperatures seasonable tomorrow as well, with day time highs approaching the mid 60s while the Keweenaw stays closer to 60.
Saturday, ridging over the eastern CONUS begins to break down and move off of the east coast, allowing the churning closed low over the Plains to open up and head into the Great Lakes, sending in waves of precipitation across the UP. Deterministic guidance is in good agreement on a secondary trough swinging in behind the lifting shortwave on Sunday, giving higher confidence that precip will linger through the rest of the weekend and into early next week. From there, deterministic guidance begins to differ on the upper air pattern Mon/Tues and even more so on the potential development of a closed low in the central US by midweek.
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.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/... Issued at 816 PM EDT Thu Sep 18 2025
Persistent NNE upslope flow continues to make SAW prone to low stratus and patchy fog once again this evening and tonight. Cigs have already deteriorated to IFR levels at SAW, but will only mention in a tempo for now, until confidence increases enough to make it the primary flight condition with next TAF issuance. Fog formation will also factor into the decision with an IFR/LIFR trend similar to last night. Elsewhere, CMX and IWD will generally be VFR with the exception of MVFR conditions at IWD in showers/storms after Fri 03Z. This has been highlighted with PROB30 groups to capture the trend through tomorrow morning and again tomorrow afternoon at IWD.
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.MARINE... Issued at 223 PM EDT Thu Sep 18 2025
Breezy NE winds 20-25 kts in the far western arm of Lake Superior diminish to 15-20 kts tonight before coming back up tomorrow afternoon between 25-30 kts out of the ENE mainly west of the Keweenaw to Duluth. There, significant wave heights will build between 4-8 feet north and west of the Apostle Islands. Gusty ENE winds begin to veer ESE late Friday into early Saturday, focusing 25 kt gusts to the central and eastern lake. The highest wave heights will be concentrated to Canadian waters and far northern lake shores. ESE winds fall below 20 kts through Sunday becoming south below 15 kts by Sunday evening. Calm conditions return early next week.
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.MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... None. Lake Michigan... None.
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DISCUSSION...BW AVIATION...TDUD MARINE...BW
NWS MQT Office Area Forecast Discussion