162
FXUS63 KDLH 041857
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
157 PM CDT Fri Jul 4 2025

.KEY MESSAGES...

- Severe storms are expected this afternoon into early Saturday
  morning - mainly for Northeast Minnesota. Damaging wind
  gusts, severe hail, and torrential rainfall with the potential
  for flash flooding are the main threats.

- Very warm and humid today for July 4th. Extreme Heat Warnings
  and Heat Advisories are in effect.

- Strong to severe thunderstorms are possible again Saturday
  across Northwest Wisconsin.

- Quieter weather to begin next week.

&&

.DISCUSSION...
Issued at 156 PM CDT Fri Jul 4 2025

We`re tracking several impactful weather concerns for this
holiday weekend.

Our most immediate concern is the oppressive heat and humidity
gripping the region today. Temperatures and humidity forecasts
continue to climb, with widespread highs now expected to reach
the low to mid 90s. When combined with dewpoints in the upper
70s to mid 70s, conditions will be truly uncomfortable. The most
intense heat will be felt across north-central Minnesota and
parts of the South Shore, where southerly winds experiencing
some downsloping from inland higher terrain will only amplify
the warming. Fortunately, areas along the North Shore should
experience a slight reprieve, thanks to cooling winds off Lake
Superior. While lingering cloud cover from morning storms,
particularly over far northern Minnesota, might offer a brief
tempering effect, the robust warm and moisture advection across
the region today will largely offset this. Were forecasting Heat
Index values in the mid 90s to low 100s, with the hottest
readings in the same areas experiencing the highest ambient
temperatures. This translates to Heat Risk values ranging from
Moderate to Major, meaning the heat could affect most
individuals sensitive to heat, or even anyone without effective
cooling or adequate hydration. Additionally, Wet Bulb Globe
Temperatures are expected to climb into the low to mid 80s. This
oppressive combination will likely impact most of the
Northland, with the exception of some portions of the North
Shore. As a result, Extreme Heat Warnings are in effect. With
Independence Day outdoor events likely, its critical that you
and those around you have plenty of water and access to cooling
options throughout the day and into this evening. Keep an eye on
grandpa if he demands another round of croquet. Since heat is
not as fun to talk about, bravo for making it this far in the
paragraph.

Onto the severe threat, we have to dissipate all of this heat
and humidity somehow, so lets drive a cold front through the
region to do that. Unfortunately, that comes with strong storm
potential - heat and humidity are the perfect snack for a hungry
storm. We anticipate strong to severe thunderstorms this
afternoon and evening and possibly into the early morning hours
on Saturday. We get a brief break Saturday morning before
another round of storms are expected further east across NW WI
Saturday afternoon and evening. Scattered showers and
thunderstorms, including strong to severe cells, will begin to
develop along a surface trough ahead of an approaching cold
front and on the edge of a northward advancing warm front. A
supercell has already formed along this front just west if
I-Falls. While this is a harbinger of what to come, the primary
synoptic forcing for ascent remains further west and should
arrive later this evening. Storms developing across far northern
Minnesota and to our west should then gradually spread
southeast during the remainder of the evening into overnight
hours. This will bring more widespread activity mainly into
north-central and northeastern Minnesota, eventually reaching
northwest Wisconsin early Saturday. At least a few of these
storms are expected to be strong to severe, fueled by 0-6km bulk
shear values around 30 knots and 3000-4500 J/kg of MUCAPE.
Storm modes are expected to quickly grow upscale into clusters
or broken lines. Given ample downdraft CAPE, the primary hazards
will be damaging wind gusts and large hail. There remains a
low, but non-zero (2%), tornado threat across far northern
Minnesota near the front during the late afternoon into late
evening hours, where storms could be surface-based and have
modest amounts of low-level helicity. This tornado threat, while
present, remains low.

Most critically, these storms have huge torrential rainfall and
significant flash flooding potential. The main threat period
for this is from late this afternoon into Saturday. Our primary
concern stems from exceptionally high Precipitable Water (PWAT)
values, which are forecast to surge to around 2 to 2.25 inches.
These values are near the maximum for July climatology,
indicating an incredibly moisture-laden airmass. This abundant
moisture, combined with a deep surface to freezing level depth
of 13,000 to 15,000 feet, creates an environment highly
conducive to efficient, heavy rainfall rates. Further
exacerbating the flood threat, deep, unidirectional southwest
winds aloft will be nearly parallel to the surface cold front
and surface trough. This alignment significantly increases the
risk of training thunderstorms, where individual storm cells
repeatedly track over the same areas, leading to prolonged
periods of intense rainfall. We anticipate multiple waves of
thunderstorms, beginning with the afternoon/evening activity and
continuing as the cold front slowly slides through the
Northland overnight into Saturday morning. Forecast rainfall
amounts have increased for north-central Minnesota, much of
northeast Minnesota, and the Arrowhead, with widespread totals
of 1 to 3 inches expected, and localized amounts potentially
even much higher. This significant threat is further
corroborated by 48-hour HREF probability-matched mean and
maximum rainfall bullseyes suggesting potential totals of 3 to 5
inches in the hardest-hit areas. While the heavy rainfall
potential drops off with southeast extent into the Twin Ports
and northwest Wisconsin, where forecast amounts of 0.5 to 1.5
inches are expected, the localized threat in north-central and
northeast Minnesota is substantial. Our WPC Excessive Rainfall
Outlook area, where a slight risk (15% chance of flash flooding)
remains, generally aligns with where a Flash Flood Watch has
been issued for late this afternoon into daytime Saturday.
Residents in these areas should be prepared for rapidly rising
water levels, inundated roadways, and the potential for flash
flooding. Some of the overnight convection last night has also
preconditioned some areas minimizing their holding capacity. An
example is a quick 1.5 of rain fell in Two Harbors from a fairly
quick moving cell this morning - this just shows you the high-
end potential of these storms. Roads were also washed out in
Washburn County last night from these dumpers.

The cold front will continue to push slowly southeast through
the Northland on Saturday, bringing noticeably less hot
temperatures with highs in the upper 70s to around 80 degrees
Fahrenheit. 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
northwest Wisconsin. Here, a plume of 1000-1500 J/kg of MUCAPE
and modest shear could produce a low-end damaging wind and small
hail threat. All storms are expected to exit to our east
Saturday night.

Cooler and drier conditions are expected for Sunday behind the
cold front, with comfortable high temperatures in the 70s and
dewpoints in the 50s to around 60 degrees Fahrenheit. Were only
anticipating isolated (10-20%) afternoon/evening shower chances.
Looking ahead to early next week, zonal mid to upper-level flow
will transition to northwesterly by mid-week. Periodic
shortwaves moving through this flow pattern aloft should bring
additional shower and thunderstorm chances at times, with
seasonal high temperatures. At this point, there doesnt appear
to be any strong signal for widespread strong to severe storm
potential early next week.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1240 PM CDT Fri Jul 4 2025

VFR for now, but an incoming system will cause widespread
thunderstorms from west to east starting this afternoon and
slowly spreading eastward overnight. +TSRA expected within the
band, so when it is over a TAF site, pretty likely that vsbys
will be < 1SM in +RA with instant ponding of water on runways.
After the storms cross, cigs will drop to sub-IFR with a slow
breakout through Saturday afternoon returning to VFR by Saturday
evening.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 156 PM CDT Fri Jul 4 2025

Potential for severe thunderstorms this evening and overnight.
Aside from that synoptic winds should be less than small craft
advisory criteria.

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 until 8 PM CDT this evening for MNZ010-
     011-018-019-025-026-033>038.
     Flood Watch through Saturday afternoon for MNZ010-011-018.
     Heat Advisory until 8 PM CDT this evening for MNZ012-020.
     Flood Watch from 7 PM CDT this evening through Saturday
     afternoon for MNZ012-019>021-025-026-033>037.
WI...Extreme Heat Warning until 8 PM CDT this evening for
     WIZ001>003-006>008.
     Heat Advisory until 8 PM CDT this evening for WIZ004-009.
MARINE...None.

&&

$$

DISCUSSION...Wolfe
AVIATION...Wolfe
MARINE...Wolfe