textproduct: Marquette

KEY MESSAGES

- This morning, Frost and Freeze headlines are in effect until 9 AM. Widespread frost is likely (50-80%) in the western UP, and patchy frost (20-40%) is possible elsewhere away from shorelines.

- Wednesday morning, areas of frost are likely (60-90%) in the western UP and patchy frost is possible (20-40%) elsewhere away from shorelines.

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

DISCUSSION

Issued at 340 AM EDT Tue Sep 22 2026

As of 06Z this morning, RAP surface analysis shows a high pressure center occupying the western portion of Quebec at 1030 mb, with trailing 1027-28 mb over the UP. From GOES Nighttime Microphysics, the more substantial cloud cover has moved south throughout the night, leaving only high, thin clouds atop some parts of the CWA. With over five hours yet to before sunrise, surface temperature observations are starting to dip into the low 30s, with most remaining in the high 30s or low 40s (excepting those within lakeshore vicinity, which sit closer to 50F). Frost and Freeze headlines are currently in effect, and temperatures are currently on track to achieve widespread frost in interior locations. Over land, winds have gone largely calm for the night except for some coastal locations which show winds mostly less than 10 mph in a land breeze pattern.

The robust Quebec high slowly propagates east through the day today while persistent ridging remains over the Upper Great Lakes. Light, easterly flow continues as the deepening Canadian high pressure deflects a compact low spinning toward the Southern Great Lakes. With highs in the low to mid 60s today, a slightly warmer low-level temperature profile in the latter half of the day will cause frost formation to struggle a bit more despite efficient (clear sky) cooling. The NBM shows a similar but slightly smaller footprint for frost tomorrow morning, with the areas of widespread frost restricted relative to the ongoing frost event. That said, areas of frost are likely in some portions of interior west (50-90%) and patchy frost is possible elsewhere (20-60%). Later this week, as surface flow turns southerly, overnight lows on Weds night/Thurs morning are unlikely to catalyze frost formation.

With dry air in place aloft, widespread relative humidities of 30- 35% are likely Tuesday late afternoon. Gaylord's 00Z sounding shows deep-layer dry air between 850 and 500 mb; modeled soundings continue to predict dewpoint depressions in excess of 20C for this afternoon. However, given light winds and highs in the 60s, conditions do not meet criteria for even borderline or limited fire weather concerns. Easterly flow persists tomorrow before beginning to veer southerly, leading to increasing low-level moisture Wednesday and Thursday, with minimum RHs in the 35-40% range on Wednesday and over 50% on Thursday.

Further out, though some low chances of precip brush the western edge of the CWA in the Thurs-Fri timeframe, the remainder of the week is setup to remain dry, with good large-scale agreement amongst ensembles into Saturday. The next chance for potentially meaningful precipitation at this time is late on Saturday into Sunday, in conjunction with a mid-level trough entering the PNW later this week.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 724 AM EDT Tue Sep 22 2026

VFR conditions prevail throughout the forecast as high pressure to the north and northeast of the region suppresses chances of fog formation below 15%. Winds will be light and variable during overnight periods, increasing to 5-10 kt during the afternoon hours out of the northeast to southeast before decreasing again in the evening.

MARINE

Issued at 340 AM EDT Tue Sep 22 2026

Light, easterly winds continue through this afternoon as the robust Quebec (formerly Ontario) high progresses slowly east. Regional high pressure persists through the week while winds veer slowly to southerly by Thursday. Periods of higher wind speeds will occur as the pressure gradient tightens at times. Friday, winds go very light (gusts < 10 knots) and waves diminish to less than 1 foot.

For Lake Superior: Light, easterly winds pick up to around 20kts in the late afternoon and evening hours Tuesday and Wednesday prior to laying down before sunrise the following day. Correspondingly, wave heights increase to 1-2ft as winds increase during the afternoon and evening hours. Thursday and Friday, winds come in generally from the south to southeast, and while gusts to around 20kts will be possible over the east-central portions of the lake Thursday (with waves to 2-3 feet), winds fall below 10kts across the entire lake Friday.

For the Bay of Green Bay and Northern Lake Michigan: Easterly flow fills in starting this morning and throughout the day today, with widespread gusts to 20 knots by noon and gusts to 25 becoming more common this evening. Winds lay down slightly (gusts to 15 knots) for a brief period Wednesday morning before increasing again in similar fashion for Wednesday afternoon and night. Winds shift over to the E/SE Thursday and Friday, falling below 15kts. Waves increase from 2- 3 feet in Lake Michigan this morning to 4-5 feet this evening before subsiding to 3 feet Wednesday morning.

MQT WATCHES/WARNINGS/ADVISORIES

Upper Michigan... Frost Advisory until 9 AM EDT /8 AM CDT/ this morning for MIZ002-005>007-009-011-013-014-085.

Freeze Warning until 9 AM EDT /8 AM CDT/ this morning for MIZ004-010-084.

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