255
FXUS63 KDLH 210529
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1229 AM CDT Thu Aug 21 2025

.KEY MESSAGES...

- Fog will expand across Lake Superior and into portions of
  northeast Minnesota and northwest Wisconsin tonight into
  Thursday morning.

- A slow-moving cold front crosses late Thursday through Friday
  with scattered rain showers and thunderstorms. A few storms
  may be strong to severe with large hail and damaging winds
  being the primary threats.

- Behind the front expect much cooler temperatures for the
  weekend into early next week with high temperatures generally
  in the 60s and lows in the 40s. Depending on cloud cover and
  winds, frost is a concern if temperatures can cool into the
  30s at night.

- Increasing west to northwest winds Saturday through Monday
  with gusts of 25-30kts will be hazardous to small craft.

&&

.DISCUSSION...
Issued at 144 PM CDT Wed Aug 20 2025

Fog and stratus are forecast to expand across western Lake
Superior this evening and tonight and spread inland over the
North and South Shores and into the Twin Ports. Dense Fog
Advisories may be needed, a 40 to 60 percent chance, for both
land and marine zones. With little airmass exchange with high
pressure and trapped low level moisture, fog formation is also
favored further inland in northwest Wisconsin, and into the Iron
Range and perhaps as far west as the Brainerd Lakes area tonight
into Thursday morning.

On Thursday, return flow on the western side of departing high
pressure will advect higher dewpoints and overall precipitable
water into the Northland through the day. Scattered rain showers
and thunderstorms are possible near the International Border
Thursday afternoon in a zone of warm air advection ahead of the
cold front. Precipitation coverage will increase Thursday
evening and night with the passage of the cold front and the
arrival of greater upper level forcing across northeast
Minnesota. With Most- Unstable CAPE values around 1000-1500
j/kg and a precipitable water axis around 1.50 to 1.75 inches,
sufficient buoyancy and moisture will be in place to support
convection that will largely be elevated. Marginal shear will be
a limiting factor for storm organization and severity,
especially with the lack of a substantial low level jet. During
the day on Friday, the cold front and moisture and buoyancy
axis shift into northwest Wisconsin. With daytime heating and a
bit greater shear with faster mid level winds, the severe threat
will be relatively higher for northwest Wisconsin on Friday
compared to northeast Minnesota on Thursday night. SPC has
maintained a Marginal Risk Thursday night and Friday, which
makes sense with a marginal hail and damaging wind threat given
the shear and buoyancy parameter space.

On Friday through Sunday, relatively deep low pressure for late
August will slowly propagate across southern Hudson Bay. Cool,
cyclonic flow around this low will yield a brief taste of Autumn
across the Northland this weekend into early next week with an
airmass characterized by 850mb mean temperatures around their
lowest 2.5th percentiles for late August. High temperatures
will be generally in the 60s Saturday through Tuesday, with
Sunday being the coolest day when temperatures may not climb out
of the 50s for some areas. Scattered rain showers and a few
embedded thunderstorms are expected Saturday and Sunday with
multiple waves embedded in the cyclonic flow with a pocket of
cool temperatures aloft. Frost will be a concern Sunday and
Monday nights, with Monday night into Tuesday morning having the
greater risk with decreasing winds as surface high pressure
builds across the area with the cool airmass in place. As
always, frost is heavily dependent on any cloud cover and how
quickly winds decrease with the stronger low and its pressure
gradient in the vicinity.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1227 AM CDT Thu Aug 21 2025

Patchy fog may develop again over the next several hours inducing
visibility restrictions at a few terminals. Any fog that does
develop will erode fairly quickly after sunrise. Radar shows a
thunderstorm complex in Southern Manitoba with a few stray showers
in the vicinity of INL. This complex should weaken later this
morning but some of its remnants may still impact INL. Later this
afternoon and evening a cold front is expected to move in from the
west. This could generate additional showers and storms, some of
which may be strong to severe. Timing is still very questionable
with high res guidance having a high variance in frontal
placement.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 144 PM CDT Wed Aug 20 2025

Light and variable winds through tonight with high pressure
settling in. Fog will expand tonight into Thursday morning and
become dense. A Dense Fog Advisory may be needed. Winds will
trend a bit breezier Thursday night into Friday with southwest
winds becoming northwest as a cold front passes through.
Scattered non-severe thunderstorms will be possible Thursday
night into Friday. Wind gusts are expected to hover around 15 kt
Thursday night into Friday outside of thunderstorms. Northwest
wind gusts to 25 kts are likely going into Saturday and Sunday
for most nearshore zones as more cooler air moves in from the
north behind a cold front.

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.

&&

$$

DISCUSSION...PA
AVIATION...Britt
MARINE...PA