035
FXUS63 KDLH 011130
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
630 AM CDT Mon Sep 1 2025

.KEY MESSAGES...

- Warm weather with scattered showers and storms through
  tonight. The strongest showers and storms will produce very
  localized heavy rainfall which could cause ponding of water in
  low-lying areas.

- Isolated to scattered thunderstorms are likely Tuesday. A few
  storms may be severe with large hail and damaging winds the
  main threats. Localized minor flooding is also possible due to
  slow storm motions and efficient rain production.

- Cooler temperatures and scattered rain showers expected
  Wednesday through the rest of the week.

- Frost Advisories may eventually be needed if winds calm down
  and skies clear Thursday morning with widespread lows in the
  30s.

&&

.UPDATE...
Issued at 628 AM CDT Mon Sep 1 2025

An area of showers and thunderstorms remained over portions of
Cook County and adjacent areas of western Lake Superior and
northwest Ontario as of 1130Z. Another area of showers appears
to have initiated off the higher terrain of the Iron Range near
Hibbing, Virginia, and east toward Isabella. Those showers were
slowly moving northward. Meanwhile a compact meso-low and
associated lobe of vorticity was noted over central Upper
Michigan via GOES-East water vapor imagery. That feature will
continue to propagate westward this morning. The additional
forcing for ascent as the meso-low approaches western Lake
Superior and the Arrowhead may be sufficient to drive an
increase in the showers and storms between now and about 15Z.
Made a few tweaks to the PoPs and QPF with this update through
15Z. Radar estimated rainfall amounts from the storms in Cook
County range from a trace up to around an inch. The greatest
accumulation so far was in a narrow area just north of Hovland
where 1.2 to 1.3 inches may have fallen.

&&

.DISCUSSION...
Issued at 424 AM CDT Mon Sep 1 2025

Early this morning...

Patchy dense fog is likely this morning. A layer of stratus
developed over portions of the Iron Range north into the
Arrowhead and north-central Minnesota over the past few hours.
Where stratus remains in place, fog potential will remain low.
Showers Sunday afternoon likely enhanced low-level moisture
available for fog. The surface pressure gradient is a little
tighter than the past few nights, so winds may not be completely
calm. ASOS and AWOS stations aren`t able to detect wind speeds
less than 3 knots, though nearby RAWS sites and CWOP stations
can. A Dense Fog Advisory may eventually be necessary if fog
becomes more widespread. Any fog which develops should dissipate
by 9 AM.

The other trend to monitor early this morning remains the
potential for isolated showers and perhaps a few brief storms.
The 01.07Z RAP continues to indicate weak isentropic lift
between the 298K to 304K surfaces. It was this weak ascent which
supported the stratus over northern Minnesota. Similar to
Saturday morning, there will likely be a few showers which
percolate over those areas early this morning. GOES-East water
vapor imagery revealed divergence aloft over the Arrowhead into
adjacent areas of northwest Ontario. The uptick in showers near
Grand Marais, MN to Upsala, ON and farther north seem to be
under the area of divergence. A few of the CAMs (NAMNest,
HiResW-ARW, HiResW-FV3, and the NSSL-WRF) suggest an increase in
coverage and intensity along the North Shore to the Twin Ports
through 12Z.

Today and tonight...

Interesting setup today across the region. A retrograde cutoff
low centered over southwest Lower Michigan as of 09Z was
situated above surface high pressure over the region. Weak low-
level theta-e advection over the region today will contribute to
500-1500 J/kg of MLCAPE by this afternoon. Weak forcing for
ascent and the possibility of latent outflow boundaries from
yesterday`s convection makes anticipating today`s showers and
storms challenging. Convergence appears best near/along the
North Shore into the Arrowhead. CAMs seem to favor scattered
showers and storms generally north of US-2 in Minnesota with
isolated convection farther south and over northwest Wisconsin.
Continue to broad brush low chance PoPs and sprinkles outside of
northern Minnesota. Effective shear of 10-20 knots will be the
main limiting factor once again today. Efficient precipitation
production is expected and there may be localized, very small,
areas of excessive rainfall under the cores of the stronger
showers and storms. Rain rates of 1 to 3 inches per hour over
very limited areas of the slow-moving storms appears likely once
again, although most areas will not see measurable
precipitation. Highs today will be warm once again with readings
in the 70s to low 80s.

Tonight will see a prefrontal shortwave trough move eastward
across northern Minnesota. Height falls and isentropic lift over
central and north-central Minnesota will support isolated to
scattered showers and a few storms overnight. Cyclonic flow over
the Arrowhead into northwest Ontario will contribute to a few
showers and storms persisting overnight in that area as well.

Tuesday and Tuesday night...

A strong cold front will sag southward Tuesday. The airmass
ahead of the front will feature continued theta-e advection
during the day. By late morning MLCAPE values will be pushing
500-1000 J/kg ahead of the front. Effective shear will be
limited early in the day and pulse storms are anticipated early
over the Boundary Waters southwest toward Bigfork. Instability
will continue to build ahead of the front and by late afternoon
MLCAPE values will be 500-1500 J/kg. Effective shear will
gradually increase over central Minnesota into northwest
Wisconsin and by late afternoon should be in the 15-25 knot
range. Greater effective shear will be noted farther west into
southeast North Dakota and northeast South Dakota. The better
effective shear will spread eastward with time. The main
question is whether the atmosphere burns through the diurnal
instability before the arrival of better shear. Still with
lengthening hodographs there will be a potential for storm-scale
organization. Forecast soundings indicate deep moisture and
efficient precipitation production is likely. There will also be
a potential for hail up to ping-pong ball size. Precipitation
loading may contribute to microbursts and localized damaging
winds. Showers will likely loiter in the wake of the front
Tuesday night.

Wednesday and beyond...

A taste of autumn returns Wednesday as cold air advection
continues in the wake of the front. Temperatures will be much
cooler with highs in the upper 40s in the Arrowhead to the upper
50s. Depending on how quickly the front passes through the
region, temperatures may be falling through the day Wednesday.
Expect rain showers off and on along with gusty winds. Lows
Wednesday night will be in the middle 30s in the Arrowhead to
around 40 in central Minnesota. A tight pressure gradient should
also winds to persist overnight limiting frost potential. There
may be a few snowflakes in the air Wednesday night as temps
continue to fall.

Thursday is shaping up mostly cloudy with scattered showers.
Winds may weaken enough Thursday night to create patchy frost.
Any showers that persist overnight will also feature a mix of
snowflakes. Conditions will be similar Friday and Saturday.

The upper-level low will begin to drift to the east on Sunday
which will allow temps to trend upward with highs in the low to
upper 60s.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 628 AM CDT Mon Sep 1 2025

Patchy fog will dissipate by about 14Z. Isolated to scattered
showers and storms remain likely over northern Minnesota today
and tonight. Added VCSH for HIB, INL, and DLH through the
afternoon. Chances are lower over northwest Wisconsin and
central Minnesota, so left precip mentions out of BRD and HYR.
Fog may redevelop tonight, although the potential for stratus
and light winds will be greater than this morning. Included
lower visibility at the sites most likely to see MVFR or lower
visibility Tuesday morning. Cold front moves through the region
Tuesday and Tuesday night and will bring showers and storms
after 02.12Z. Winds will veer northwesterly and become gusty
behind the front.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 424 AM CDT Mon Sep 1 2025

High pressure will remain in place over the region today. 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.

A cold front is forecast to move across western Lake Superior
Tuesday. 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 through the end of the
week. Seasonably warm water temps will contribute to persistent
stronger winds and conditions hazardous for smaller vessels.

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...Huyck
AVIATION...Huyck
MARINE...Huyck