489
FXUS63 KDLH 040538
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1238 AM CDT Fri Jul 4 2025

.KEY MESSAGES...

- Isolated strong to severe storms are possible late this
  evening into Friday morning, mainly for northwest Wisconsin
  and far north-central Minnesota. Localized damaging wind gusts
  and small to marginally severe hail are the main threats.

- Very warm and humid on July 4 (Friday). Heat Advisories have
  been issued.

- Strong to severe thunderstorms are possible during the
  afternoon/evening on July 4 (Friday) and Saturday
  afternoon/evening. Heavy rain could lead to some flash
  flooding concerns as well.

&&

.DISCUSSION...
Issued at 223 PM CDT Thu Jul 3 2025

Current Conditions - Tonight:

Prominent southerly flow through the day has lead to temperatures
climbing into the mid and upper 80s this afternoon. Aside from some
fair weather cumulus and some hazy skies in northern MN this
rest of the afternoon continues to be quiet. Looking upstream we
can see a cluster of precipitation over the Red River Valley
tracking east. This area of interest is spurned from a
shortwave rounding the apex of an upper level trough. 12Z suite
of deterministic guidance brings this shortwave through the
Brainerd Lakes region this evening and into NW WI overnight.
CAMs are showing some increased consistency with this so we have
introduced PoPs of 15% through the period. If convection does
manage to develop there is a moderate amount of instability
available with bulk shear of 40 kts. This convective parameter
space would allow for a marginal threat (1 out of 5) for large
hail and damaging winds to develop.

As the night goes on there will be two features to be on the lookout
for. A warm frontal boundary extending across WI and up through MN
and an elongated low pressure system over the Northern Plains. CAMs
are beginning to agree on showers and storms ramping up in the
early morning hours along the warm frontal boundary and
carrying this activity east. Meanwhile, back in the Northern
Plains, another sector of showers and storms are set to fire up
and move NE possibly clipping our northwest counties. A
nocturnal low level jet will be ramping up overnight with speeds
in excess of 40 mph further aiding the development and
sustainability of convection. While still conditional the
convective parameter space is conducive to a marginal risk (1
out of 5). Damaging winds is the primary concern with any storms
that would develop in these early morning hours.

Friday - This Weekend:

Several impactful weather concerns for the Friday/Saturday timeframe:

1) Heat and humidity for Friday, 2) Strong to severe thunderstorm
potential Friday and Saturday afternoons/evenings, and 3) Heavy
rainfall and flooding potential Friday evening into Saturday.

Independence Day (Friday) has seen a continued slight upward trend
in the temperature and dewpoint forecast as the apex of the upper-
level ridge slides overhead. Remnant storms in northern MN and
northwest WI will be sliding east of the area by late morning, which
may complicate the high temperature forecast a bit depending on the
duration of lingering cloud cover, though strong warm air and
moisture advection should still offset this a bit. Widespread
dewpoints in the upper 60s to low 70s and high temperatures away
from Lake Superior in the upper 80s to locally mid 90s are expected,
though high temperatures in the 70s to mid 80s from the Twin Ports
up the North Shore near Lake Superior are expected due to winds off
the Lake. This will lead to widespread heat indices in the low to
upper 90s away from Lake Superior, and maybe even some pockets of
100F heat indices. Heat Risk values will also be widespread Moderate
values (heat affects most individuals sensitive to heat) to some
pockets of Major values (heat affects anyone without effective
cooling or adequate hydration). A Heat Advisory has been issued for
all of the Northland aside from the North Shore for late Friday
morning through mid evening. Because of this oppressive heat and
humidity is occurring on Independence Day when outdoor events will
be more common, it will be particularly important to plan ahead and
ensure that you and those close to you have plenty of water and
places to go to keep cool.

Regarding precipitation/storm potential, scattered shower and
thunderstorm development and potential isolated strong to severe
storms return as early as later this afternoon into tonight. A low
pressure system approaching from the Northern Plains/Canadian
Prairies on Friday should put most of the Northland solidly in the
warm sector of the low pressure. A capping inversion should hold
across most of the area as the better synoptic forcing for ascent
remains moreso over the Dakotas. By late Friday afternoon/early
evening, the cold front/surface trough should be situated from
central South Dakota northeast towards International Falls as
falling heights aloft and low level convergence begins to initiate
storms along and just ahead of the front. Storms should then slowly
spread southeast during the remainder of the evening into overnight
hours mainly in central to northeastern MN on a more widespread
basis. Some of these storms should be strong to severe on a more
widely scattered basis with 0-6km bulk shear values of 30-35 kt and
1500-3000 J/kg of MUCAPE to initially work with, though instability
does drop off with time later in the evening and overnight and storm
mode becomes a more messy cluster rather quickly. The primary hazard
would be damaging wind gusts given plenty of downdraft CAPE, with
large hail as a secondary threat, particularly initially in the late
afternoon/early evening when storms have yet to congeal before the
hail threat quickly decreases. There is also a period of time late
afternoon into the late evening where storms could be surface based
and have just enough low-level helicity for a non-zero tornado
threat (2%, the lowest SPC Convective Outlook threshold for tornado
mention) across far northern Minnesota near the front. This tornado
threat remains very limited at best.

A deep layer of southwest winds aloft being parallel to the surface
cold front would point to a heavy rain and at the very least a
localized flash flooding potential Friday evening into Saturday.
PWATs increase to around 2" and the surface to freezing level depth
being around 13-15,000 feet will create a threat for training storms
to produce efficient, heavy rainfall rates with multiple waves of
thunderstorms from the afternoon/evening storms and then continued
thunderstorms as the cold front actually slides through the
Northland overnight into Saturday morning. It still doesn`t look
like flooding would be an issue for most locations, but some
portions of the Brainerd Lakes into the Iron Range and Arrowhead
would be favored the most for 1-2" of rainfall, with potential
localized amounts of 2"+ (25-35% chance in the Iron Range) for
Friday through Saturday. Rainfall probabilities drop off with
southeastward extent into the Twin Ports and northwest WI.
Probabilities of >1" of rainfall in the Twin Ports are around 40-50%
and taper off to 20-40% in northwest WI through Saturday. WPC has
upgraded our excessive rainfall outlook from a marginal risk
(5% chance of flash flooding) to a slight risk (15% of flash
flooding).

As the cold front continues trekking southeast through the Northland
on Saturday, with noticeably less hot temperatures with highs in the
upper 70s to low 80s. There remains a short window of time Saturday
afternoon and evening where a few strong to severe storms will be
possible once again, primarily in northwest WI along and ahead of
the cold front depending on how cloud cover and lingering
precipitation from overnight storms impacts instability.

Largely cooler and drier for Sunday behind the cold front with highs
in the 70s and more comfortable dewpoints in the 50s to around 60.

Early Next Week:

Zonal mid to upper-level flow for early next week turning
northwesterly for mid-week. It looks like there will be periodic
shortwaves moving through this flow pattern aloft, which should
bring additional shower and thunderstorm chances at times with
seasonal high temperatures. There doesn`t appear to be any strong
signal at this time for strong to severe storm potential early next
week.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1238 AM CDT Fri Jul 4 2025

As a warm front lifts northeast through the area during the
current overnight into early morning, roughly 09-13Z some MVFR
conditions could be possible at KDLH and KHYR due to isolated to
scattered thunderstorm development along the front, though
confidence in direct impacts to the terminals remains a bit in
question due to uncertainty into how far north thunderstorms
develop. An additional cluster of showers and storms over
southern Manitoba and northeast North Dakota will track east
later during the current overnight through the early morning
hours, mainly impacting KINL and possibly KHIB as it moves east.
MVFR conditions and gusty and erratic winds up to around 30-40
knots can`t be ruled out with the storms, particularly for KINL.
We then see a break in precipitation potential for much of today
with VFR conditions before additional thunderstorms develop
along a surface trough/cold front later this afternoon and
evening mainly near KINL and areas west before storms gradually
shift east into central and northeast Minnesota this evening
into tonight. MVFR to IFR conditions will be possible with this
second round of storms in heavy rain, along with some strong to
severe storm potential with gusty thunderstorm winds. Some low
level wind shear is also possible this evening into tonight at
most terminals along and ahead of the cold front.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 223 PM CDT Thu Jul 3 2025

Northeast winds across the lake will continue through the overnight
period with the strongest winds being found at the head of the lake.
Overnight there will also be some storms that may develop along a
warm frontal boundary and pass over the Lake during the early
morning hours. Activity will taper off before once again
ramping up in the overnight period where more widespread storms
and showers will be possible. Winds will also switch from out of
the east to the southwest Friday night.

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

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
MN...Heat Advisory from 11 AM this morning to 8 PM CDT this evening
     for MNZ010>012-018-019-025-026-033>038.
WI...Heat Advisory from 11 AM this morning to 8 PM CDT this evening
     for WIZ001>004-006>009.
MARINE...None.

&&

$$

DISCUSSION...Britt
AVIATION...Rothstein
MARINE...Britt