527
FXUS63 KDLH 121142
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
642 AM CDT Fri Sep 12 2025

.KEY MESSAGES...

- Dense fog will gradually dissipate late this morning. Dense
  Fog Advisories in effect near Lake Superior shoreline in
  Minnesota and near the Twin Ports.

- There is a 10-30% chance of thunderstorms north of US-2 this
  morning. A few storms may be strong this morning over north-
  central Minnesota. Storm chances increase to around 10-30%
  over the remainder of the Northland this afternoon and
  evening.

- Above normal, summer-like, temperatures this weekend with
  highs in the low 70s to low 80s.

- On and off chances for showers and thunderstorms return Sunday
  night and continue through much of next week.

&&

.DISCUSSION...
Issued at 426 AM CDT Fri Sep 12 2025

Fog and low stratus moved inland from Lake Superior over
portions of east-central and northeast Minnesota. GOES-East
night microphysics imagery revealed additional low stratus and
fog developed over portions of northwest Wisconsin inland from
Lake Superior due to radiational cooling and light winds. Fog
and low stratus are expected to continue expanding early this
morning. For the moment the area under a Dense Fog Advisory
seems appropriate as the low stratus was inhibiting radiational
cooling. We will continue to monitor trends and potentially
expand the advisory if visibilities worsen. Visibility and
stratus is expected to gradually dissipate by late this morning.

Showers and storms were located along the Canadian border west
into northeast North Dakota and southern Manitoba as of 08Z. The
storms were located on the nose of a 20 to 35 knot southerly
low-level jet centered along the Dakotas/Minnesota border. The
nose of the jet was in an area of tightly packed pressures in
the 296-308K isentropic surfaces. While instability was meager
near Baudette and International Falls (MUCAPE of up to 750 J/kg
per 08Z RAP mesoanalysis), the additional vertical ascent from
the isentropic lift continued to support and expand the area of
precipitation. Farther west, where stronger MUCAPE of 1000-2000
J/kg was found, a cluster of strong to severe storms was located
near Devils Lake, ND. The 06Z RAP shows MUCAPE expanding
eastward into northwest Minnesota ahead of the storms in the
next few hours. The low-level jet will begin to veer farther
eastward and slowly weaken with time through 14Z. At this point
the storms should begin to outpace the instability before they
reach western edges of Cass, Itasca, and Koochiching counties
thus weakening before entering our forecast area.

After 14Z the forecast details get a little murkier. CAMs are
having difficulty capturing the ongoing convection. The 07Z HRRR
and 06Z NAMNest seem to have a decent handle on the current
conditions while the 07Z RAP has a more believable evolution
through this morning. The low-level jet will continue to weaken
into the afternoon. The area of tighter pressure packing
mentioned above is forecast to sag southward with time and
should still be well aligned with the nose of the jet. So even
while the magnitude advection dwindles, there should be
sufficient lift to keep showers and a few embedded storms in the
picture over northern Minnesota into the afternoon, mainly
along and north of US-2.

Additional storms are forecast to develop over western
Minnesota this afternoon and move into central and east-central
Minnesota and northwest Wisconsin this afternoon. Meanwhile
loitering precipitation from the morning convection should be
propagating eastward across the Arrowhead. Elevated instability
will gradually increase over Minnesota during the afternoon as
evidenced by MUCAPE values of 1000-2000 J/kg. Hodographs over
central Minnesota around 21Z feature favorable curvature in the
0-3km layer and then sharply reverse that curve in the 3-9km
layer. Effective sheer around 20 to 30 knots is forecast,
although the hodograph shape suggest enhanced ascent in the low
levels and then less favorable pressure perturbations farther
aloft. The elevated nature of the storms suggests they won`t be
able to utilize all of the low-level enhancement and we expect
low-centroid storms with efficient rainfall production. Overall
think the risk of severe storms is low and not zero. A few
rambunctious storms may produce hail up to quarter size and
downdraft winds of 40 to 60 mph. WPC has included much of our
forecast area in a Marginal risk of excessive rainfall today.
Given the forcing and efficient rain production potential, we
think the risk of localize minor flash flooding warrants that
risk category.

High pressure ridging continues heading into the weekend.
Another night of dense fog is likely which will be aided by
today`s rainfall. Once the fog clears Saturday, expect warm
temperatures. Persistent low-level theat-e advection will
continue and temperatures should climb into the middle 70s to
middle 80s (with upper 60s along the North Shore), or about 10
to 15 degrees above normal (except again for areas very near
Lake Superior where temps will be near normal). Sunday will
trend even warmer with widespread 80s away from Lake Superior.
The Arrowhead and lower St. Louis River Valley will see
temperatures in the middle 60s to upper 70s. The areas away from
Lake Superior will be 10 to 20 degrees above normal. Saturday
and Sunday will both be dry. There is a small chance of
thunderstorms over central and north-central Minnesota late
Sunday night/early Monday morning.

A southerly nocturnal low-level jet will develop Sunday night
and Monday morning. This will provide support for another round
of storms over the Red River Valley. The storms may propagate
into central and north-central Minnesota before sunrise. The
latest model runs have generally kept the storms farther to our
west and out of our area. A low pressure system over the
northern Plains Monday will push a surface warm front northward
across our area. The chance of rain and storms will increase
Monday afternoon and evening. Additional rounds of thunderstorms
are forecast Tuesday night through the end of next week. Given
the very warm, summer-like, conditions across the area, it`s
reasonable to think some of the storms will be strong.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 639 AM CDT Fri Sep 12 2025

Fog and low stratus will improve by 16Z. Scattered rain showers
and a few thunderstorms will persist through the day and sag
southward with time. Additional storm development is forecast
later this afternoon and may impact BRD, DLH, and HYR. Fog
redevelops tonight after skies clear.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 426 AM CDT Fri Sep 12 2025

Dense Fog Advisory remains in effect this morning for the
waters of the North Shore and from Duluth to Sand Island, WI.
GOES-East satellite imagery suggests the fog cleared over the
waters farther east from Sand Island. Isolated to scattered
storms are forecast this afternoon. There is about a 10-20%
chance of storms over the water. A few may be strong with wind
gusts to 35 knots and penny size hail. Northeast winds will
strengthen again today over the southwest arm of Lake Superior.
Sustained winds of up to 16 knots with gusts up to 20 knots are
forecast. Conditions will be similar tonight and Saturday with
areas of fog developing and winds weakening overnight. Winds
strengthen again Saturday. The pattern repeats again for Sunday.
A chance of storms returns Monday.

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

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
MN...Dense Fog Advisory until 10 AM CDT this morning for MNZ020-021-
     037.
WI...Dense Fog Advisory until 10 AM CDT this morning for WIZ001.
MARINE...Dense Fog Advisory until 10 AM CDT this morning for LSZ140>146.

&&

$$

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