textproduct: Marquette

KEY MESSAGES

- Light lake-enhanced showers will be possible (~30%) especially along the terrain of the western and north-central UP this morning.

- Gusty northeast winds will cause hazardous swimming conditions and rip current risks along Lake Superior today.

- Dry pattern with high pressure sets up through much of next week. Below-average temperatures expected through Wednesday (including morning frost potential), giving way to above-normal temperatures late week.

DISCUSSION

Issued at 312 AM EDT Sun Sep 20 2026

Early morning GOES-East Nighttime Microphysics RGB imagery shows a wide variety of cloud structures, though KMQT radar returns have all but entirely fallen off entirely. MRMS estimates of rainfall today have been highly variable, with some locations along the state line getting no measurable precip, but some locations as far north as northwest Delta County and southern Marquette County seeing between 0.1 and 0.2 inches. The 500mb pattern currently consists of ridging over the south-central US and over the West Cost separated by a cutoff low over Wyoming with building ridging over the Canadian Prairie. A dry shortwave is noted over northern Ontario by RAP analysis and water vapor imagery.

Today, a cold front associated with the Ontario trough drops southeastward over Lake Superior and into the UP. Weak forcing and a lack of moisture will lead to spotty showers at most with the front itself. However, the surge of cooler air aloft will cause marginally- supportive thermodynamic profiles for some lake-enhanced or lake- effect rainfall, with CAMs showing the orographic forcing of the western and north-central UP being enough to force weak precipitation, though QPF will be low. This will also come with some gustier NE winds, with gusts of 20+ MPH forecast especially along the Lake Superior shores. This in turn cranks wave heights up to 6 ft within 5 miles of the Lake Superior shoreline, which will drastically increase the risk of hazardous rip currents and challenging swimming conditions for those trying to squeeze in a late-September Sunday beach day at Lake Superior beaches. A Beach Hazard Statement will be issued before sunrise today, lasting until sunset. Waves falling below 3 ft by Monday morning will cause the hazards to wane over at least Alger County, though uncertainty still persists in whether conditions will relax enough for Marquette County to not need another Beach Hazard Statement to kick off the work week. Clearing skies overnight will allow temperatures tonight to fall to the 30s away from the shores of the Great Lakes. Patchy frost is currently forecast as there is some uncertainty in the timing of clearing and how effective radiational cooling will be. However, if more certainty is granted by the day's models, a Frost Advisory may become necessary.

In the wake of the weekend disturbances, the ridging to the north of the trough amplifies, causing split flow. This results in dominant surface high pressure establishing over northern Ontario and Quebec through much of next week, likely bringing an extended period of dry weather to the UP. The latest NBM keeps us dry until Sunday but even then, the precipitation signal is not particularly strong. Upstream ridging aloft results in cooler continental flow aloft, and being on the south/southwest periphery of a surface high results in cool easterly to northeasterly flow at the surface off of the Canadian Shield. This brings cool conditions for the beginning of the week with a gradual warming trend as the week goes on. For instance, the NBM even calls for up to 50% chances of sub-freezing temperatures for Tuesday morning, though the LREF chances are significantly lower. By the end of the week, NBM highs are widespread 70+. The CPC 6-10 and 8-14 day outlooks both show 50+% chances for the UP to be in above average temperatures for the end of September and a slight favoring of below normal precipitation (30-40% chance).

AVIATION /06Z TAFS THROUGH 06Z MONDAY/

Issued at 107 AM EDT Sun Sep 20 2026

VFR/MVFR cigs present early this morning deteriorate to MVFR/IFR at IWD/SAW as a cold front sweeps across Lake Superior through day break. Given NE upslope flow, cant rule out a few showers or drizzle at SAW, thus have introduced prob 30s for -shra between ~12-15z. Conditions improve to MVFR/VFR through the late morning to afternoon as drier air works into the area. Otherwise, breezy NE winds 15-25 kts are expected at all sites behind the frontal passage.

MARINE

Issued at 312 AM EDT Sun Sep 20 2026

High pressure building to the north today in addition to gusty winds mixing down in the wake of a Hudson Bay cold front looks to bring 20- 30 kt northeast gusts to most of Lake Superior. Waves across Lake Superior (especially in the south and the west) build to 4-6 ft. Waves increase to near 3 feet over northern Lake Michigan and Green Bay by Monday as well due to prolonged easterly flow approaching 20 kt. For the beginning of next week, high pressure building over Northern Ontario opposing low pressure over the Lower Mississippi Valley will drive some gradient wind gusts to around 20 kt out of the east before model spread and forecast uncertainty increases late in the week.

MQT WATCHES/WARNINGS/ADVISORIES

Upper Michigan... None. Lake Superior... None. Lake Michigan... None.