NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 251154
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
654 AM CDT Thu Jun 25 2026

.KEY MESSAGES...

- There is a chance for widely scattered showers and
  thunderstorms east of I-39 this afternoon, with highest
  chances (35-45%) in east central WI.

- Active shower/storm pattern develops for Saturday night
  through Wednesday next week.

- A strong warming trend is expected early next week,
  potentially nearing Heat Advisory criteria Monday through
  Wednesday.

&&

.UPDATE...
Issued 650 AM CDT Thu Jun 25 2026

Stagnant rain-humidified air over central portions of Lake
Michigan has lead to an area of marine dense fog north of a Port
Washington to Whitehall MI line for which an Advisory has been
issued. Models expect this fog to erode out by mid to late
morning. Patchy dense fog over land areas (low-lying marshy
areas and river valleys in central WI) will burn off much
faster (early this morning) under the sunshine.

Continuing to monitor the potential for widely scattered showers
(and possibly a few weak thunderstorms) to develop over portions
of eastern and east-central WI this afternoon, mainly between
Noon and 6 PM CDT. These should be very brief / widely scattered
/ weak if applicable, lightning should be the only concern.
Modeled SBCAPE fields only hit 300-750 joules in this area.

Sheppard

&&

.SHORT TERM...
Issued 1249 AM CDT Thu Jun 25 2026

Overnight through Sunday:

Storms diminished and most of southern WI is suddenly under
clear skies. With that and the light winds and the recent heavy
rain, we are now seeing patchy fog developing. Patchy dense fog
can be expected through 7 AM. It is uncertain how transient or
widespread this fog will be, but we will issue a dense fog
advisory as necessary.

The combination of a lake breeze convergence and a weak mid
level shortwave will combine over central/east central WI this
afternoon and give us a chance of diurnally-driven thunderstorms.
The model soundings show weak CAPE up to 500 j/kg (HREF shows
MU CAPE of 500 to 750 j/kg) and up to 30 kt bulk shear. This
supports scattered thunderstorm development with a very small
chance for a stronger cell or two, but this is not a severe-type
setup. Lightning is the main hazard.

With surface high pressure over the Upper great lakes and
onshore flow over southern WI on Friday, highs be cooler than
normal in the lower to mid 70s (except upper 70s west of
Madison).

A weak shortwave trough is expected to track across the Central
Plains on Saturday, but storms associated with this feature
should remain south of southern WI due to the easterly winds
over us holding that warm front south. However, we have small
chances of storms in the forecast due to the close proximity of
the forcing. The upper level ridge should push into southern WI
on Sunday, so our chance for storms is lower that day.

Cronce

&&

.LONG TERM...
Issued 1249 AM CDT Thu Jun 25 2026

Sunday Night through Tuesday:

A closed upper low will sit over the Pacific Northwest and
southwest Canada from Saturday through Tuesday. Another low will
follow for the rest of the week. This will create a surface low
in the Northern Plains and draw warm, moist air into the Upper
Midwest on southerly winds from the Gulf. This air mass is
expected to arrive behind a warm front Sunday night-Monday
morning and generally remain in place all week. It looks like
the warm front should lift through southern WI quietly (without
storms) due to the timing.

The main story is the heat and humidity that will impact
southern WI next week. It looks like the models are trending a
little later with the arrival time of this heat, but once it
moves in (by Monday morning), temps should be in the lower 90s
since 925mb temps are forecast to be around 25C with dry
adiabatic low level lapse rates. If these temps pan out due to
the dry low levels, then it seems unlikely that we will actually
achieve dewpoints in the mid 70s like what is currently in our
forecast. Models have a pretty high dewpoint bias, so I am
skeptical about the forecast heat index values we have in the
extended.

The other scenario is that our dewpoints end up in the
mid 70s, but then we would not have that dry adiabatic mixing
and end up with highs in the upper 80s. So realistically, heat
indices should be around 100 which is heat advisory criteria. I
am uncertain about reaching the extreme heat warning criteria of
105 for southern WI due to the above reasons.

In addition, all it would take to lower the temps/heat indices
during this warm spell would be clouds and remnant
showers/storms from storms that develop to our north or
northwest along the "ring of fire" at the top of the ridge where
the low level jet will be pointing. There are differences
between the models about how close this area will be to southern
WI, so this will be something to watch.

Cronce

&&

.AVIATION...
Issued 650 AM CDT Thu Jun 25 2026

Areas of fog and low stratus over east-central WI and the WI
river valley should burn up and clear out rapidly under the
strong sunshine early this morning. After that, looking at
diurnal cumulus clouds between 4,000 and 7,000 ft AGL across the
region, with chances for widely scattered showers and weak
thunderstorms over eastern and east-central WI terminals this
afternoon (PROB30 groups included in TAFs where applicable).
These should be relatively weak / minimally disruptive storms if
applicable, instability in the atmosphere appears quite limited.
A light northwesterly breeze expected across the region today,
with a lake breeze developing right along the shoreline of Lake
MI this afternoon and making some inland progress later this
afternoon. Generally 10 kt or less sustained wind speeds with
all of this.

Dry weather tonight with nearly calm winds. Some scattered
high-altitude clouds (generally over 20,000 ft) should help to
reduce fog potential tonight. The best shot at seeing any fog
would likely be in the WI River Valley as usual.

Sheppard

&&

.MARINE...
Issued 1249 AM CDT Thu Jun 25 2026

Weak low pressure over northeast Wisconsin will slide into
northern Lower Michigan by Thursday morning. Patchy fog is
possible overnight. High pressure over Ontario and the western
Great Lakes will dominate Friday through Saturday with light
north to northeast winds likely. Sunday, low pressure deepens
over the Central Plains, bringing breezy southeasterly winds to
the lake. Winds turn southerly and strengthen into Monday as low
pressure exits into the Canadian Prairies. On and off
thunderstorms become more likely during this time.

Cronce

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Dense Fog Advisory...LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-LMZ643-
     LMZ669-LMZ868-LMZ870 until 11 AM Thursday.

&&

$$

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