textproduct: Marquette

KEY MESSAGES

- Chance of rain (30-50%) mainly south of US-2 this evening through Saturday evening. Chances of 1/3 inch of rain are less than 10% for all except southern Menominee County.

- Low temperatures in the upper to mid 30s for the eastern UP and isolated interior western UP locations will lead to a 20-40% chance of frost formation. Those with sensitive outdoor vegetation should keep an eye on the forecast.

- Dry pattern with high pressure sets up Saturday night through much of next week. Fall-like temperatures in the early part of the week trend warmer by the end of the week.

DISCUSSION

Issued at 247 AM EDT Fri Sep 18 2026

Early morning GOES-East Nighttime Microphysics RGB imagery shows a mixture of high clouds streaming in from the west associated with a shortwave causing thunderstorms in Nebraska and South Dakota as well as low stratus and at least some patches of FG (confirmed by METARs reporting FG at SAW as well as others around the region). This combination of cloud types should keep low temperatures from falling out of the 40s this morning except for a few isolated typical cold spots. Fog is not anticipated to become widespread.

The 500mb pattern consists of 599 dam ridging over Arkansas bounded by deep troughs centered over the Pacific Northwest, the Bahamas, and northern Quebec. The aforementioned ridge-riding shortwave currently over western South Dakota will track a surface low south of the UP this weekend and bring chances of rain to the southern UP today and Saturday. The trend of rainfall southward continued in a big way over the past 24 hours, with 00Z HREF showing meaningful (15+%) probabilities of even a half a tenth of an inch of rain by 00Z Sunday being limited to the immediate vicinity of the state line and Menominee County south of US-2. The 12Z LREF does at least shift some ~20% chances of measurable rainfall a bit further into the UP, but impactful rainfall will be certainly south of the UP as even the 90th percentile of the LREF (reasonable worst case) is less than an inch even for the Menominee area (and less than a third of an inch for all of the UP except for Menominee County south of US-2). With the drying trend in the forecast, especially with easterly flow descending off the Canadian Shield, overnight lows into Saturday morning look to be around the mid 30s in the interior east and in some isolated locations of the interior west, which would lead to frost potential (20-40% chance, especially for elevated surfaces). Those in the eastern UP with sensitive vegetation outdoors should monitor the forecast as the trend has been colder, but if cloud cover from the southern disturbance extends further north than currently forecast, temperatures may not fall enough for frost formation.

In the wake of the disturbance, the western CONUS trough will shift into the Northern Plains Sunday, weakening slightly. At the same time, ridging to the north of the trough amplifies, causing split flow. At this time, the favored solution is for the UP to be affected by the northern branch of this split flow which will lead to persistent high pressure and dry weather and near-normal to slightly below normal temperatures for Sunday through at least the first few days of next week until ensemble spread increases for the midweek and beyond. 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 /12Z TAFS THROUGH 12Z SATURDAY/

Issued at 737 AM EDT Fri Sep 18 2026

VFR will be the main flight category as TAF sites remain under the influence of high pressure. Light winds continue through the afternoon, shifting east as the day progresses. Low pressure passing south of the region will bring increasing cloud cover and the potential for showers at IWD. Confidence remains low in how far north the showers will spread, so will continue to highlight with PROB30s only at IWD.

MARINE

Issued at 247 AM EDT Fri Sep 18 2026

Through Saturday, low pressure passing by to the south combined with a high to the north will result in prolonged northeasterly flow into the western arm of Lake Superior, with winds increasing locally to 20 kt and waves of 2-3 feet. A stronger high building to the north on Sunday looks to expand coverage of 20-30 kt winds to most of Lake Superior. Models disagree about gale potential, with the Euro ensemble probabilities of gales now less than 10% while the NBM projects gale chances of around 40%. Should the gale solution be preferred, waves across Lake Superior (especially in the south and the west) would 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.