860
FXUS63 KDLH 031739
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1239 PM CDT Sun Aug 3 2025

.KEY MESSAGES...

- Stagnant weather pattern remains in place with a strong high
  pressure over the region trapping smoke at the surface. Air
  Quality Alerts remain in effect across the Northland

- A slow pattern change begins this afternoon with precipitation
  chances of 20-40% entering from the west.

- A Rex blocking pattern sets up over the Northland leading to
  off and on rain and thunderstorm chances through the mid week,
  largely for the MN side.

&&

.UPDATE...
Issued at 1050 AM CDT Sun Aug 3 2025

Forecast remains largely on track. Updated PoPs through this
evening to raise values. Multi-day MCV over west-central
Minnesota late this morning is forecast to meander north-
northeast this afternoon. Forcing for ascent associated with
this feature will persist. Light rain and showers should expand
in coverage in response to daytime heating. RAP13 forecasts of
potential instability through this evening remain low with less
than 500 J/kg of MUCAPE forecast over central and northern
Minnesota. Lifted Indices from the NAM and GFS both trend
negative over the northern third of Minnesota this afternoon
suggesting a few lightning strikes are possible despite the
unremarkable CAPE values.

&&

.DISCUSSION...
Issued at 134 AM CDT Sun Aug 3 2025

Current Conditions/Today:

The anomalously strong surface high pressure that has been
present over the region for the last several days has begun to
weaken and will slowly shift to the southeast through the day.
Return flow on the backside of the air mass will bring southerly
winds into the region. Aerosol optical depth from yesterday
afternoon showed that the Canadian Wildfire smoke had penetrated
as far south as central MI. While winds turning out of the
south would normally flush the region of smoke, these antecedent
conditions may lead to extensions in the Air Quality Alerts.

Sunday Night - Tuesday Night:

With the return of southerly winds we will see an increase in
moisture advection and warming temperatures. Ridging aloft moves
off as well with some shortwaves moving in from the west. 00Z
guidance shows an upper level low currently over western ND
slowly encroaching on the Northland late Sunday. High pressure
aloft over Manitoba will act as a Rex Block leading to slow
movements with this system. Overall synoptic forcing looks to be
on the weak side with showers and storms getting the best boost
from diurnal processes. The expectation at this time will be
for scattered showers with an isolated storm or two through
Tuesday. This will primarily take place over MN as WI will still
have subsidence in play suppressing potential for rain. The
convective parameter space is lacking in overall bulk shear and
instability remains weak leading to no severe weather
anticipated at this time.

Midweek:

Late Tuesday the blocking pattern begins to break down as
surface low moves across the Canadian Prairies. An increased low
level jet will also help to pivot the baroclinic zone out of
the Red River Valley an into the Northland. A slight uptick in
instability may help to produce some stronger storms Wednesday
evening, but bulk shear is still on the marginal side clocking
in around 33 kts.

End of the Work Week:

As head into the latter parts of the work week the forecast
becomes a bit more uncertain. Looking at water vapor transport
we will see a surge from the Central Plains up into the
Northland, likely a combination of some Gulf moisture and
evapotranspiration. This added moisture will leave us with an
unstable environment. Most of the uncertainty is with the upper
pattern and what shortwaves will be rounding the dominant anti-
cyclone over the desert southwest. The GFS is the most robust
with it`s latest run for Thursday and it has some agreement from
the GEFS ensemble as the CSU ML severe probabilities begin to
light up for Thursday. For now we will have to wait and see if
this signal stays consistent and if any other ensembles begin to
lean this way as well.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1239 PM CDT Sun Aug 3 2025

Slow-moving upper-level low pressure system centered over SE ND
this afternoon will continue to meander slowly north-
northeastward this afternoon. An area of light rain over west-
central and central Minnesota is forecast to move northward and
expand eastward this afternoon with scattered showers expected
to develop east of the main area of persistent rain. A few
lightning strikes are possible this afternoon despite limited
potential instability. The greatest chance of a storm is near
INL. Forecast models are struggling with the location and
affects of the upper-level low, so confidence in the
precipitation portion of the forecast is low. Smoke will loiter
around the terminals this afternoon and evening. Visibility
forecasts due to smoke are medium confidence and will vary
between 6SM and 4SM. Cloud cover at HIB overnight should limit
the fog potential there, while partial clearing over HYR may
permit IFR fog to develop overnight.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 954 AM CDT Sun Aug 3 2025

High pressure will be begin to depart today as an upper-level
low pressure system moves into western Minnesota. Winds will
begin the day from the southwest around 5 knots. Winds along the
South Shore to the Twin Ports may back southeasterly this
afternoon and evening. There is a 20-40 percent chance of gusts
of 22-25 knots between Grand Portage and Isle Royale this
afternoon. Similar to yesterday, however, winds near the water
surface will remain below the threshold for a Small Craft
Advisory. Winds are forecast to back easterly and northeasterly
on Monday as the surface high drifts farther from the lake and
weak low pressure develops over the northern Plains. Wind and
waves may become hazardous for smaller vessels in the southwest
arm of Lake Superior during the afternoon and evening hours. The
trend for easterly and northeasterly winds will persist Tuesday
and Wednesday. At the moment wind speeds are expected to be 5
to 12 knots. Later forecasts may need to increase wind speeds
and gusts in the southwest arm if confidence increases.
Additionally, there may be areas of smoke across the lake at
times over the next several days.

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