NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 031046 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
546 AM CDT Thu Sep 3 2026

.KEY MESSAGES...

- Hot and humid condition continue with heat indices in the 90s
  and approaching 100 toward the WI/IL border.

- Periods of showers and storms will be possible today into
  Friday, with this evening/tonight's round capable of producing
  strong to severe thunderstorms with damaging winds and heavy
  rainfall being the main threats.

- Drier weather expected for the weekend into early next week,
  with warm and humid conditions persisting.

&&

.UPDATE...
Issued 546 AM CDT Thu Sep 3 2026

Isolated to scattered showers and storms are possible this
morning into the afternoon as a weak wave moves through a warm
and unstable airmass and a stalled frontal boundary remains in
the vicinity. Stronger forcing and more flow aloft are then
likely this evening into tonight, with more widespread
thunderstorm activity expected. It still looks like this latter
round may produce a few strong to severe storms, with locally
heavy rainfall also possible. There remains uncertainty with
where exactly the storms will set up later, with some models
just clipping the northeast forecast area, while others develop
the storms right over the southern Wisconsin.

Very warm and humid conditions are expected today, especially in
the southern forecast area on the more humid side of the stalled
front. Heat indices may approach or hit 100 again in these
areas, especially given enough afternoon sunshine.

DDV

&&

.SHORT TERM...
Issued 103 AM CDT Thu Sep 3 2026

Today through Friday:

The hot and humid airmass in place over the region will
continue today. Looking at temps creeping back into the mid-
upper 80s and dewpoints in the 70s resulting in heat indices
especially along and south of I-94 warming back into the 90s and
approaching 100F toward the WI/IL border this afternoon. Then
cooling into the 70s and upper 60s overnight, but still
remaining humid.

This airmass will continue to be conducive for periods of
shower and thunderstorm development. However, it will depend on
timing, forcing, and alignment of the forcing as well as
influences from any prior activity.

The first of these periods will be into the early morning
hours. Seeing a few weak showers across northeastern IA moving
into southwestern WI along weak ribbon of a 25 kt LLJ, but given
the strong capping inversion and not much additional forcing
this activity remains limited through the early morning.

Further back to the west across the lower Missouri River
Valley, the main core of the LLJ sits and is progged to
strengthen to around 40 kt through daybreak. Based on the 00z
CAMs this will be the focus for shower and storm development
through daybreak and is progged to latch onto the stalled
frontal boundary stretching across southern MN/northern IA and
track eastward along it into central WI through the mid to late
morning. Mainly expecting this to bring increased PoP chances
for the northern half of the CWA into the early afternoon. But
still could see some of these showers and storm bleed further
south depending on if they are able to push out outflow.
Overall, this round will progress through and exit by early
afternoon and not expecting strong or severe storms with this
round given lack of shear.

Despite the heat and humidity the afternoon into the early
evening is looking predominately dry as the stalled front is
expected to remain to the north and lack of any forcing to get
things going. However, if the mid-late morning round does kick
out any outflows or gravity waves, then wee cannot rule out
seeing some isolated to scattered development during this time.
While not expecting stronger storms, instability is expected to
recover with SBCAPE ranging from 1000-2000 J/kg by this time and
meager deep layer shear could be enough for a taller storm or
two and will be capable of producing gusty winds. Again the
potential remains lower at this time to see this scenario
materialize.

The main window of concern will be later this evening into the
overnight timeframe. This is when the moisture (PWATs
approaching 2 inches), instability (SBCAPE +1000 J/kg), and deep
layer shear (+40 kt) align with the stall frontal boundary,
500mb lobe of vorticity, 700mb frontogenesis, and +35 kt LLJ.
00z HREF shows the theta-E gradient setup from northwest to
southeast across our eastern half of the CWA. With this setup,
model continue to prog storms developing to the north this
evening and traveling along this gradient into our neck of the
woods. With dynamics and synoptic forcing aligning, it will
favor the potential for stronger to severe storm development.
May concern with any stronger storms will be damaging winds/wet
microbursts potential. Also if this activity goes linear as
model sounding suggest, then cannot rule out an embedded spin up
or two as well. While, things are trend toward this scenario
early in the day convection and any lingering influence could
disrupt this pattern. However, will need to see how things play
out through the morning and will be best to monitor trends
through the day, but remain vigilant as potential remains.

In addition to the storm potential, this juicy airmass will
also support efficient rainfall rates with any stronger/taller
storms. QPF totals could range any where from under an inch to
even seeing pockets of 3 inch rainfall (90th percentile). While
the antecedent conditions support the ground being able to take
this rainfall, higher hourly rainfall rates along with any rain
training over the same area could lead to ponding and minor
flooding.

Forecast into Friday becomes more conditional and uncertain
after this round as some models suggest things linger all the
way through Friday morning while other have things wrapping up.
Nonetheless, scattered shower and storm chances linger into
Friday as the frontal boundary persists across the region. Also
expect the hot and muggy conditions to linger as well.

Wagner

&&

.LONG TERM...
Issued 103 AM CDT Thu Sep 3 2026

Friday night through Wednesday:

An upper-level ridge is progged to gradually build across the
Upper Midwest Saturday with the ridge axis gradually expected to
slide east through the start of next week. However, the front
that has been the focus for pesky, scattered shower and
thunderstorm activity through the end of the week looks to
linger for another day strewn across our southern half of the
CWA into Saturday. Pair the surface boundary and hot, muggy
airmass with a little bit of a ripple of mid- level vorticity,
some 700mb frontogenesis banding, and a 30-40 kt LLJ may be just
enough forcing to support additional shower and thunderstorm
chances for Saturday. The main factor affecting this activity
into Saturday will be the forcing aligning and the placement of
the surface boundary as it depends on prior days activity which
could end up pushing things further south into IL or may sit
somewhere across southern WI. Nevertheless, a potential will be
there.

Otherwise, the rest of the weekend is trending drying as the
ridge slides further east and high pressure builds over the
Great Lakes region. Most models prog this high setting up to our
northeast which will increase easterly flow off of Lake
Michigan. Thus, expecting some milder temps in the 70s to lower
80s as well as lower dewpoints in the 60s for the end of the
weekend into the start of next week. This pattern is set to
persist through at least Tuesday as another high builds down
across central Canada into the Great Lakes and reinforce this
pattern along with easterly flow off of Lake Michigan. Then long
range models trends are favoring a warm up ahead of a trough
passage through the middle of next week along with the potential
for additional shower and thunderstorm chances.

Wagner

&&

.AVIATION...
Issued 546 AM CDT Thu Sep 3 2026

Isolated to scattered showers and storms are possible this
morning into the afternoon, with more widespread thunderstorm
activity expected this evening into tonight. This latter round
may produce a few strong to severe storms, with locally heavy
rainfall also possible. There remains uncertainty with where
exactly the storms will set up later, with some models just
clipping the northeast forecast area, while others develop the
storms right over the southern Wisconsin.

Patchy fog will linger in the east early this morning, with
mainly VFR conditions then expected the rest of today into
tonight outside of lower ceilings and visibilites in
thunderstorms.

Light and variable winds early this morning will become westerly
by late morning, then transition to easterly by this evening.
Winds will likely turn easterly early in the day near the lake.
Light east to southeast winds are then expected tonight.

DDV

&&

.MARINE...
Issued 103 AM CDT Thu Sep 3 2026

A stationary frontal boundary will remain across the Great
Lakes region through Friday. As this frontal boundary waffles
north to south across the lake from day to day, generally east
to northeast winds are expected north of the front, with east to
southeast winds south of the front. On and off thunderstorms
will be possible along and north of this frontal boundary
through at least Friday night. Then high pressure over Hudson
Bay on Saturday, while low pressure moves into the northern
Great Plains. Similar to earlier week storms, widespread severe
weather is not anticipated, though isolated stronger storms with
hail and gusty winds are possible this evening/tonight.

Wagner

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...None.
&&

$$

Visit us at weather.gov/milwaukee

Follow us on Facebook, X, and YouTube at:
www.facebook.com/NWSMilwaukee
www.x.com/NWSMilwaukee
www.youtube.com/NWSMilwaukee