106
FXUS63 KDLH 041150
AFDDLH

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

.KEY MESSAGES...

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

- Very warm and humid today, July 4th. Extreme Heat Warnings and Heat
  Advisories have been issued.

- Strong to severe thunderstorms are possible during the
  afternoon/evening on July 4 (today) and Saturday
  afternoon/evening. Heavy rain may lead to flash flooding,
  particularly in north-central and northeast Minnesota this
  evening into Saturday.

&&

.DISCUSSION...
Issued at 449 AM CDT Fri Jul 4 2025

Current Conditions - This Morning:

Two areas of focus for strong to potentially severe storm
concerns through early/mid-morning today: 1) northwest
Wisconsin and 2) far north-central Minnesota.

For northwest WI, scattered thunderstorms have been developing
along an 850-mb convergence boundary north of the surface warm
front, where a pool of 1500-2200 J/kg of MUCAPE and effective
bulk shear around 30 knots has kept storms mostly upright, but
provided just enough organization to keep a strong to marginally
severe (Level 1 out of 5) hail and wind gust threat going
through around 7-8 AM this morning. Hail of nickel to quarter
size and wind gusts of 50-60 mph would be the main threats, and
threats should be relatively short-lived (30 minutes or so) with
any individual storms. Can`t rule out some localized heavy rain
potential either given slow storm motions. Shower/storm
intensity should weaken with eastward extent into mid-morning.

For far northern MN, an area of scattered to widespread showers
and thunderstorms has developed northeast of the surface low
pressure near the intersection of the warm front and a surface
trough boundary. Downdraft CAPE appears a bit more abundant up
that way along with the edge of a 2000-3000 J/kg MUCAPE
gradient. There have been upstream reports of wind gusts up to
around 50-60 mph, but the expectation is for these storms to
eventually outrun the better downdraft CAPE as the early morning
progresses, which should limit the eastern extent of the 50-60
mph wind gust potential as storms move farther east into
northern St. Louis County. Should see some efficient rainfall
rates in these storms as well given PWAT values around 2" (high
end of climatology for July), with a quick 0.5-1" of
accumulation not out of the question.

Today - Saturday:

Several Impactful weather concerns persist for today into
Saturday.

1) Oppressive heat and humidity today, 2) Strong to severe
thunderstorm potential this afternoon and evening and Saturday
afternoon and evening, and 3) Heavy rainfall and flooding
potential late this afternoon into Saturday.

Temperatures and humidity forecasts for today have increased
once again, with widespread highs now forecast to reach into the
low to mid 90s along with dewpoints in the upper 60s to mid 70s.
The hottest temperatures should be in north-central MN, as well
as in parts of the South Shore due to some downsloping of
southerly winds from the inland higher terrain. Areas along the
North Shore should see a slight reprieve from the hottest
temperatures due to winds off of Lake Superior. Lingering cloud
cover from morning storms, particularly over far northern MN,
could hamper temperatures slightly, but the robust warm
advection and moisture advection over the area today should
offset this dampening effect. With Heat index values in the mid
90s to low 100s (hottest in the same areas where the highest
temperatures will be), Heat Risk values of Moderate (heat
affects most individuals sensitive to heat) to Major (heat
affects anyone without effective cooling or adequate hydration),
and Wet Bulb Globe Temperatures in the low to mid 80s, this
oppressive heat will likely impact most of the Northland aside
from portions of the North Shore. As such, most of the Heat
Advisories across the Northland were upgraded to Extreme Heat
Warnings. Because of this oppressive heat and humidity occurring
on Independence Day when outdoor events will be more common, it
will be particularly important to ensure that you and those
close to you have plenty of water and places to go to keep cool
today and into this evening.

For the strong to severe storm potential: scattered shower and
thunderstorm development-- including strong to severe storm
potential--will occur along the surface trough ahead of the cold
front mid to late this afternoon and evening from South Dakota
into northwest and far northern MN. A capping inversion in place
across most of the remainder of the Northland should hold as
the better synoptic forcing for ascent remains farther west.
Storms across far northern MN and to our west should then slowly
spread southeast during the remainder of the evening into
overnight hours mainly in north-central to northeastern MN on a
more widespread basis and eventually into northwest Wisconsin
early Saturday. At least a few of these storms should be strong
to severe with 0-6km bulk shear values around 30 kt and
2000-3500 J/kg of MUCAPE to initially work with, with
instability slowly decreasing off towards the later evening and
overnight. Storm modes grow upscale into clusters/broken lines
rather quickly, so the primary hazard would be damaging wind
gusts given ample downdraft CAPE, with large hail as a secondary
threat given the messier storm mode. In the late afternoon into
the late evening where storms could be surface based and have
modest amounts of low-level helicity, there remains 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 continues to be low at best.

For the heavy rain and flash flooding potential: Deep
unidirectional southwest winds aloft will be parallel to the
surface cold front and surface trough. PWATs increase to around
2-2.25" (near maximum of July climatology) and the surface to
freezing level depth around 13-15,000 feet deep will create a
threat for training storms to produce efficient, heavy rainfall
rates. 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 will produce heavy rain and the potential for
flash flooding late this afternoon into Saturday. Forecast
rainfall amounts for north-central MN into much of northeast MN
and the Arrowhead have increased, with 1-3" expected and
localized amounts even higher. This is corroborated by 48-hour
HREF probability-matched mean and maximum rainfall bulleyes of
3-5". Heavy rainfall potential drops off with southeast extent into
the Twin Ports and northwest WI, where forecast rainfall amounts
of 0.5-1.5 inches are forecast for later today through Saturday.
Our WPC excessive rainfall outlook area where a slight risk
(15% of flash flooding) remains across portions of north-central
to northeast MN, generally aligned with where a Flash Flood
Watch has been issued for later today into daytime Saturday.

The cold front slowly pushes southeast through the Northland on
Saturday, with noticeably less hot temperatures with highs in
the upper 70s to around 80F. There will be a short window of
time Saturday afternoon and evening where a few strong to severe
storms will be possible once again along and ahead of the cold
front in far northeast/eastern MN and northwest WI where a plume
of 1000-1500 J/kg of MUCAPE and modest shear could produce a
low-end damaging wind and small hail threat. Storms exit to our
east Saturday night.

Cooler and drier for Sunday behind the cold front with highs in
the 70s, more comfortable dewpoints in the 50s to around 60, and
only some isolated (10-20%) afternoon/evening shower chances.

Previous Forecast for 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 /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 649 AM CDT Fri Jul 4 2025

Scattered showers and storms continue to track northeast over
western Lake Superior and east across the International
Border/far northern Minnesota early this morning. There have
been some widely scattered showers popping up farther south into
central Minnesota and KHIB vicinity, but don`t anticipate
additional thunderstorm development there. Expect most of the
convection this morning to move east by mid morning, 15-16Z,
with VFR conditions outside of any storms. Additional
thunderstorms develop along a surface trough ahead of a cold
front later this afternoon and evening mainly near KINL first,
and then storms from areas west move east into KHIB and KBRD
later this evening and into KDLH tonight before finally getting
to KHYR towards the very end of the TAF period. MVFR to IFR
conditions will be possible with these later storms in heavy
rain, along with some strong to severe storm potential with
gusty thunderstorm winds and possibly some small hail. Some low
level wind shear should also return this evening into tonight
at KHIB/KDLH/KHYR along and ahead of the cold front, with
ceilings quickly dipping to IFR behind the storms tonight, as
well.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 439 AM CDT Fri Jul 4 2025

Northeast winds across the lake will continue through early this
morning, with the strongest winds at the head of the lake.
A warm frontal boundary passing over the Lake early this morning
could produce a few thunderstorms with localized wind gusts to
30-40 kt. Activity will taper off today before once again
ramping up in the evening to overnight tonight where more
widespread storms and showers will be possible. Winds will also
switch from out of the east to the southwest Friday night and
northwest Saturday PM, with gusts remaining at or under 20 kt.

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

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
MN...Extreme Heat Warning from 11 AM this morning to 8 PM CDT this
     evening for MNZ010-011-018-019-025-026-033>038.
     Flood Watch from 4 PM CDT this afternoon through Saturday
     afternoon for MNZ010-011-018.
     Heat Advisory from 11 AM this morning to 8 PM CDT this evening
     for MNZ012-020.
     Flood Watch from this evening through Saturday afternoon for
     MNZ012-019-025-026-033>036.
WI...Extreme Heat Warning from 11 AM this morning to 8 PM CDT this
     evening for WIZ001>003-006>008.
     Heat Advisory from 11 AM this morning to 8 PM CDT this evening
     for WIZ004-009.
MARINE...None.

&&

$$

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