textproduct: Marquette

KEY MESSAGES

- Hazardous swimming conditions and high rip current risks are present through this afternoon for Marquette County due to high wave heights from the northeast.

- Widespread frost likely (50-80%) in the western UP Tuesday morning, and patchy frost possible (20-40%) elsewhere away from shorelines.

- Dry pattern with persistent high pressure sets up through much of this week. Below-average temperatures through Wednesday gives way to above-normal temperatures late week..

DISCUSSION

Issued at 333 AM EDT Mon Sep 21 2026

This morning, RAP surface analysis shows expansive high pressure centered over the eastern Province of Ontario at 1027 mb. Light, anticyclonic flow dominates over the region; while much of the UP shows calm conditions, flow is north-northeasterly where nonzero. Temperatures currently range from the low 30s to the mid 50s. Locations interior tend to be lower, particularly the west; lakeshores remain anchored in the 50s thanks to nearshore lake surface temps near 60F. GOES Nighttime Microphysics shows high cloud cover working its way west across the UP, with thicker clouds making an appearance near the WI border and across the northern tier. Likely this will hinder the downward trend in temperatures across the west, limiting frost formation this morning.

The Ontario high pressure center deepens and tracks east tomorrow, setting up a Hudson Bay High pattern to the northeast with a Plains trough immediately to the southwest. As the surface high, reinforced by mid-level flow, strengthens into Wednesday, the Plains trough moves south toward the Lower Midwest, and clear skies prevail by the second half of tomorrow. Modeled soundings show deep-layer dry air with substantial (>20C) surface dewpoint depressions both today and tomorrow afternoons, and forecast minimum RHs are in the high 30s this afternoon in isolated spots and in the high 20s in the western interior (widespread 30s elsewhere) tomorrow afternoon. That said, critical fire weather conditions will be far from achieved given light winds <10 knots and high temperatures in the low 60s for the next few days.

With temperature observations tonight quickly outpacing the going forecast and dry air and clear skies on the way, efficient radiational cooling is anticipated for Monday night. Thus, widespread frost is likely (50-80%) in the western UP Tuesday morning, and patchy frost is possible (20-40%) elsewhere away from shorelines.

The split flow pattern slowly moves east of the Great Lakes region into Thursday as high pressure persists over Ontario/Quebec into the weekend. Slight variations in LREF clusters make their appearance beginning on Saturday, general consensus exists that some form of regional ridging is likely through Sunday. Thus, below-average high temperatures (5-10 below on Monday) gradually warm into above- average high temperatures (5-10 above on Saturday) by the weekend while conditions remain dry.

AVIATION /06Z TAFS THROUGH 06Z TUESDAY/

Issued at 112 AM EDT Mon Sep 21 2026

VFR conditions and light winds prevail overnight. High pressure working just north of Lake Superior will keep light easterly winds <15 kts in the forecast and dry weather through Monday.

MARINE

Issued at 333 AM EDT Mon Sep 21 2026

Winds continue to diminish as high pressure builds in from the north. The robust Ontario high will lead to slowly veering surface winds from the northeast this morning to southerly on Thursday. As the high deepens and tracks east through Thursday morning, brief periods of higher wind speeds will occur as the pressure gradient tightens at times. After Thursday, winds go very light (gusts < 10 knots) and waves diminish to less than 1 foot.

For Lake Superior, wave heights to 4 feet subside throughout today with light winds less than 10 knots. This evening, NE'ly flow increases to gusts to 20 in nearshore zones, and 20-25 knots on the western lake (just east of the Apostles) where funneling occurs. Otherwise light easterlies pick up again Tuesday and Wednesday evenings while waves remain less than 2 feet.

For the Bay of Green Bay and Northern Lake Michigan, sustained light winds less than 10 knots increase this evening to gusts to 20 knots. While sustained winds remain light (<10 knots) through the next few days, gusts to 15-20 knots remain possible for the majority of Monday evening through Wednesday morning. Waves remain below 2 feet.

MQT WATCHES/WARNINGS/ADVISORIES

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