253
FXUS63 KDLH 221138
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
638 AM CDT Fri Aug 22 2025

.KEY MESSAGES...

- Patchy fog is expected early this morning, with some areas of
  dense fog reducing visibility to 1/4 mile in north-central
  Minnesota.

- Strong to severe thunderstorms will be possible this afternoon
  and early evening, mainly over northwest Wisconsin. Damaging
  winds and large hail are potential hazards.

- Cooler, fall-like temperatures are expected this weekend into
  early next week. Frost may be possible, especially on Tuesday
  morning, for inland locations away from Lake Superior.

&&

.DISCUSSION...
Issued at 420 AM CDT Fri Aug 22 2025

As of early Friday morning, a weak cold front is draped across the
CWA around the Iron Range. This cold front is associated with
vertically-stacked low pressure located near Hudson Bay, which will
slowly propagate east today through tonight. Patchy fog has
developed early this morning around and behind the cold front, with
some areas in north-central MN seeing areas of dense fog reducing
visibility to 1/4 mile. This fog is expected to dissipate shortly
after sunrise as diurnal heating begins.

A secondary, and stronger, cold front is expected to enter into the
CWA this afternoon and evening as the axis of the 500mb trough
associated with the vertically-stacked low moves into the
Borderlands. This cold front this afternoon and evening is likely to
develop showers and thunderstorms, with the greatest potential being
over northwest WI. A few strong to severe thunderstorms will be
possible as well, as southwest flow advects moist dewpoints in the
upper 60s to low 70s into the CWA ahead of the cold front. This will
increase MLCAPE into the 1000-1600 J/kg range this afternoon over
northwest WI and adjacent areas in eastern MN. Wind shear will be
slightly less favorable today, with 0-6km bulk shear in the 25-30
knot range with messy hodographs.

Timing for convective initiation today will most likely start
after 18z based on recent runs of the CAMs, with a line of
discrete cells initially forming before transitioning more into
a linear storm mode. Potential hazards include damaging winds up
to 60 mph, as DCAPE values approach 1000 J/kg, and large hail
up to 1". Given the lack of appreciable low-level curvature
appearing in hodographs, tornadoes are not expected today. As
the cold front continues to progress eastward, thunderstorms
will exit the area this evening.

Conditions following the cold frontal passage today into tonight
will be much cooler and fall-like as we head into the weekend. Low
temps tonight are expected to be around 10 degrees cooler in the
upper 40s to low 50s. Temps this weekend will be unseasonably cool,
with highs in the upper 50s to mid 60s. Cyclonic flow aloft on
Saturday will likely lead to scattered light rain showers across the
area.

With the more fall-like conditions persisting into early next week,
this introduces the potential for frost. There is currently around a
20% chance that low temps on Monday night into Tuesday morning drop
below 40 degrees per the deterministic NBM. However, it is worth
noting that this deterministic solution from the NBM is above the
75th percentile of the probabilistic data and is showing a warm
bias. Therefore, the expectation is that low temps on Tuesday
morning will likely be in the 30s for locations away from Lake
Superior. A Frost Advisory may be needed if trends hold.

Besides the potential for frost early next week, the pattern beyond
today will be fairly benign as a large ridge develops upstream of
the CWA.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 638 AM CDT Fri Aug 22 2025

Morning fog is expected to dissipate over the next couple hours as
daytime heating begins. Cigs are expected to improve to VFR across
the region this morning for most terminals. The exception will be
lingering MVFR cigs around KHYR ahead of the cold front. Strong to
severe thunderstorms will be possible in northwest Wisconsin this
afternoon, exiting by this evening. Westerly winds will be breezy at
times through the period. Fog is unlikely again tonight, as drier
air moves into the area following a cold frontal passage.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 420 AM CDT Fri Aug 22 2025

Southwest winds are expected today ahead of a cold front, which will
move through western Lake Superior this afternoon and evening. West
to northwest winds are expected to increase following this cold
front, with gusts up to 25 knots. Small Craft Advisories remain in
effect for all of western Lake Superior starting late this evening
and continuing through Saturday evening. A second surge of cooler
air on Sunday may keep the pressure gradient elevated, which may
necessitate an extension of the Small Craft Advisory through the day
Sunday and even through Sunday night. Waves this weekend will be
highest in the outer Apostle Islands, with heights up to 4 feet.

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...Small Craft Advisory from 10 PM this evening to 10 PM CDT
     Saturday for LSZ121-140>148-150.

&&

$$

DISCUSSION...Unruh
AVIATION...Unruh
MARINE...Unruh