584
FXUS63 KMQT 210734
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
334 AM EDT Mon Sep 21 2026

.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.

&&

$$

DISCUSSION...RE
AVIATION...BW
MARINE...RE