697
FXUS63 KDLH 020600
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
100 AM CDT Tue Sep 2 2025

.KEY MESSAGES...

- Warm Tuesday before a significant cold front will bring a
  pattern change and cool down through Saturday.

- Several rounds of rain, with the strongest potential for
  organized storms on Tuesday as a cold front pushes through in
  the afternoon into the evening. Large hail, localized minor
  flooding, as well as gusty wind will be the primary hazards.

- Starting Wednesday night, there will be the potential for
  frost with overnight lows dropping into the 30s for areas in
  northern Minnesota.

&&

.UPDATE...
Issued at 100 AM CDT Tue Sep 2 2025

A cluster of showers and storms over northwest Minnesota will
continue to propagate south-southeast over the next several
hours along CAPE gradient which stretched from near Roseau to
near Redwood Falls. The higher instability values of 500-1500
J/kg of MLCAPE were located in the Red River Valley with lower
values farther east in central and north-central Minnesota. RAP
forecasts show this gradient building slightly farther east
through sunrise with the magnitudes decreasing slightly over
that time. Effective shear remains weak at 15 to 25 knots.
Expect upright pulse storms to continue with the strongest cells
on the western periphery of the cluster. The storms will
propagate into the Brainerd Lakes in the 2-4 AM timeframe.
Occasional lightning and wind gusts of 25 to 30 mph are the most
likely hazards.

Meanwhile cyclonic flow aloft persists over northwest Ontario
and the western Great Lakes. Divergence was noted north of Grand
Marais and Grand Portage in adjacent areas of northwest
Ontario. I would not be surprised to see gradual development of
showers and storms in that area again tonight.

The remainder of the forecast appears to be on track for now.

&&

.DISCUSSION...
Issued at 240 PM CDT Mon Sep 1 2025

A beautiful Labor Day is underway, with temperatures in the 70s
across most of the region. Lingering showers over the Arrowhead
from this morning have mostly dissipated, leaving the forecast
area partly to mostly sunny for the afternoon.

Scattered showers are possible this evening, with the highest
chance (40%) along and north of Highway 1, as indicated by the
HREF. The current airmass has satellite TPW values of ~1.10",
which is just above climatological average (for IFalls).
Instability is expected to build this afternoon along the North
Shore, with muCAPE values exceeding 1000 J/kg. Given weak shear,
any storms that develop are likely to be slow-moving, efficient
rain produces, similar to those observed over the past 24
hours.

A second shot at rain will arrive overnight as a shortwave
trough and an associated moisture plume moves in from the
Dakotas, bringing isolated showers. With the wave sweeping
through, these should move a little more quickly, but will still
maintain the potential for efficient rainfall (60+Td and
1.20 to 1.30" PW).

Temperatures are forecast to reach in to the 70s for one last
day before a significant shift. A potent cold front will push
into central MN early Tuesday afternoon, bringing the highest
chance for organized storms this period. Surface dewpoints will
have not changed (60+) ahead of the front, and mlCAPE building
around 1,500 J/kg, especially as the front enters NE MN. As it
pushes south, CAMs suggest the better instability pushes south
quickly. Regardless, this should support a line of storms
developing along the front Tuesday afternoon and tracking
southeast through the evening.

A few limiting factors: Will there be clearing behind the
shortwave and ahead of the front? In addition, the main upper
level forcing will trail the cold front, limiting shear with the
front. However, given the strength of the incoming wind fields,
there is a threat of stronger gusts with any that can mix down
to the surface. If full storm potential is reached, ping pong-sized
hail, localized minor flooding, as well as gusty wind will be
the primary hazards.

A stark contrast in temperatures is expected on Wednesday as
colder air arrives. Expect highs in the 50s and gusty winds,
making it feel even cooler. This is due to a chilly, cyclonic
flow from an upper-level low swirling over the GL. This pattern
will keep scattered rain showers in the forecast daily through
the weekend, with overnight temperatures dropping in Northern MN
into the 30s. A few wet snowflakes may even mix in with the
rain in the North.

The primary concern for the latter half of the week is frost.
If breaks in the clouds and calmer winds occur, esp on Thurs and
Fri mornings, widespread lows in the 30s may even be possible.
This rainy, cool pattern will persists through Saturday. With
warming possible starting on Sunday as the pesky low finally moves
away.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 100 AM CDT Tue Sep 2 2025

Another night of monitoring visibilities is on tap. A cluster
of showers and storms will continue to propagate south-
southeastward through 12Z and may gradually weaken with time.
Latest timing has that cluster moving into the BRD area around
08Z. Where skies remain clear and winds are light, fog appears
likely. The main concern is the potential development of stratus
and the affect of the cluster of storms on wind speeds over the
region. With the exception of BRD, I left fog mentions in place
for now.

Showers and storms are expected to develop today ahead of a
cold front. I tried to narrow down the time of the greatest
impacts and moved thunderstorms into PROB30 groups. Forecast
models don`t have a great handle on the amount of
destabilization ahead of the front and the CAMs feature very
diverse solutions. Therefore overall confidence in timing precip
and storm chances trended lower with this forecast.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 315 PM CDT Mon Sep 1 2025

High pressure will remain in place over the region this evening.
This will keep winds generally less than 10 knots from the
southwest. Isolated showers and storms are likely today and
tonight. Occasional cloud-to-water lightning will be the main
threat from the storms, along with locally gusty wind.

A strong cold front is forecast to move across western Lake
Superior Tuesday afternoon. Showers and thunderstorms are
expected with the front. Winds will veer northwesterly and
increase in speed behind the front. Conditions will become
hazardous for small craft. Cool air will continue to pour into
the area Tuesday night, lasting through the end of the week.
Seasonably warm water temps will contribute to persistent
stronger winds and conditions hazardous for smaller vessels.
Windy conditions continue on Wednesday morning and afternoon,
causing hazardous conditions to continue for small craft.


For the open water discussion, refer to the NWS Marquette Area
Forecast Discussion at weather.gov/mqt.

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
MN...None.
WI...None.
MARINE...None.

&&

$$

UPDATE...Huyck
DISCUSSION...LR
AVIATION...Huyck
MARINE...LR