textproduct: Marquette

KEY MESSAGES

- A few light showers in the east diminish this afternoon.

- Cooler on Sunday with isolated to scattered showers in the north half.

- Chilly Sunday night with patchy frost in the interior.

- Widespread rain moves into the UP from west to east late Monday into Monday night, ending Tuesday morning.

DISCUSSION

Issued at 140 PM EDT Sat Sep 12 2026

Early afternoon water vapor and RAP imagery show a closed upper low over southwestern Hudson Bay (500 mb heights at 10pctl of climo) with strong zonal flow over the northern tier of the west half of the CONUS. Band of clouds associated with departing moist axis is over the eastern half of the UP with clearing skies to the west. Surface front is coincident with this band of clouds, along which a band of showers/sprinkles is occurring from eastern Alger SW through Dickinson County. Cannot rule out an isolated TS over Schoolcraft/Luce through early this afternoon with dewpoints in the low to mid-60s and SBCAPE 500-1000 J/kg per SPC Mesoanalysis. Otherwise, winds shift NW behind the front, ushering in a cooler and drier airmass as lower heights associated with the Hudson Bay low pivot across the upper Great Lakes. LREF mean 850 mb temps fall to 2- 3C over Lake Superior on Sunday, which is 15-20pctl of climo, and should result in some lake-induced instability with surface to 850 mb delta-Ts around 13C. CAMs show lake-effect rain showers developing during the late morning into afternoon, particularly over the east half as the dry column will be more prominent over the west.

Sunday night, ideal radiational cooling conditions develop as PWATs fall to 0.3-0.4 in (5-10pctl of climo) associated with a building ~1025mb high. Have reduced lows relative to NBM guidance Monday morning, with widespread 30s in the interior and patchy frost expected.

Another closed upper low shifts from the northern Rockies into central Canada early next week, with a strong LLJ feeding Gulf moisture poleward ahead of it. This will boost PWATs up to 1.5-1.75 inches Monday night, and an area of rain will move from west to east along the nose of the LLJ across the UP late Monday into Monday night. This looks to be a fairly quick-hitting system with most of the rain having exited east of the UP by Tuesday morning, but should provide at least a wetting rainfall for the entire area. A blend of LREF and NBM probs of > 0.50" in 24 hours are 50-80%, and > 1.00" are 30-50%, lowest over the Keweenaw and highest over the south- central. Cluster analysis shows variability with respect to precip amounts is tied to the 500 mb heights in central Canada - a deeper trough resulting in a stronger low actually results in a drier solution for the UP, possibly due to the LLJ forcing moving through quicker.

Temps should be fairly seasonable on Monday, and a sneaky warm day is possible Tuesday with mixing into warm temps aloft in the wake of the Monday night system. The rest of the week looks fairly seasonable as we are favored to be on the northern extent of the persistent positive height anomaly over the south-central US, although proximity of a moisture plume along the edge of this high means we can't rule out some rain toward the middle/end of the week.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 157 PM EDT Sat Sep 12 2026

Cigs and vis are expected to remain VFR for all sites through 18z, although CMX will see ceilings dropping to ~3,500ft around 12z Sunday. Winds will remain WNW over all terminals, with gusty conditions to remain over IWD until this evening and to remain over CMX through the overnight hours. Cloud cover is expected to gradually increase over all terminals this evening, resulting in BKN sky conditions overnight. Western terminals will see SCT conditions return Sunday morning, while SAW remains under BKN through 13z.

MARINE

Issued at 140 PM EDT Sat Sep 12 2026

Lake Superior: Westerly winds behind a cold front continue today with 25-30 kt common, and a few gusts touching gale force cannot be ruled out. Winds may relax somewhat tonight, but the arrival of a pocket of cold air aloft will cause stronger winds to mix to the surface on Sunday, with 25-30kt W-NW winds expected again, and a few gusts to 35 kt over south-central portions of the lake. Significant wave heights of 3-6 feet will be common. Small craft advisories remain in effect through Sunday. High pressure briefly results in diminishing winds Sunday night into Monday, but strong southerly winds will increase through the day on Monday as the high shifts east. Although stability will be increasing, temperatures should be cool enough at the onset to mix some of the stronger low-level jet winds to the surface, with a 50-70% probability of southerly gales developing over the east half of the lake Monday night, likely peaking around 40 kt. A brief period of westerly gales is likely (50- 70%) in the vicinity of the Keweenaw to Stannard Rock on the back side of this system on Tuesday, with winds quickly diminishing Tuesday night.

Northern Green Bay and northwestern Lake Michigan: Winds and waves should continue diminishing for the rest of today into tonight as they shift westerly. However, northwesterly winds will increase to near Small Craft Advisory criteria on Sunday as colder air aloft moves over the waters. Winds diminish Sunday night as high pressure builds in, but the next period of active marine weather occurs late Monday into Monday night with strong S-SW winds developing. Probability of gales is 30-40% at this time Monday night, and waves build to around 6 feet in the bay, and 6-10 feet in the nearshores of Lake Michigan. Wind and waves gradually diminish through the day Tuesday as they shift westerly.

MQT WATCHES/WARNINGS/ADVISORIES

Upper Michigan... Beach Hazards Statement until 8 PM EDT this evening for MIZ014.

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