NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 020440
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1140 PM CDT Wed Jul 1 2026

.KEY MESSAGES...

- An Extreme Heat Warning remains in effect for all of southern
  Wisconsin through Thursday evening.

- Thunderstorms are expected overnight, with highest chances
  north of a line from Lone Rock to Sheboygan. Damaging winds
  and heavy rainfall.

- There are periodic chances (40 to 60 percent) for
  thunderstorms Thursday into the holiday weekend. Some strong
  to severe storms with heavy rainfall may occur at times,
  though confidence remains low with the timing of each round of
  storms. This may impact outdoor holiday activities at times,
  so keep up with the forecast.

&&

.SHORT TERM...
Issued 1139 PM CDT Wed Jul 1 2026

Overnight through Friday:

Thunderstorms congealed into somewhat of a line over central and
southwest WI this evening. There are a few segments that are
tracking west to east that are organized, cold-pool-driven and
producing 40 to 60 mph winds. As these storms track into
portions of southern WI overnight, our environment support wet
microbursts with its mid level dry air, high instability, and
sufficient shear. Wind is our main concern. The northern two
tiers of counties (north of Madison and Milwaukee) are in a
Severe Thunderstorm Watch until 5 AM. The late end time on this
is to allow for storms to get across most of Lake Michigan.

As the night goes on and the cluster of storms takes on a more
east-west orientation, we are going to have an increasing
flooding risk. With PWATs pushing 2 inches, individual storms
can have 1 to 2 inch per hour rain rates, and repeated rounds
of these storms with high rainfall rates will quickly add up.

Thursday (today): A shortwave tracking through the Midwest is
exptected to arrive in southern WI during the afternoon which
should trigger thunderstorms. If the overnight showers/storms
diminish in a timely manner this morning, this will give us
enough time to clear out and destabilize. The more sun, the
higher the instability for stronger storms. Overall, there will
be decent synoptic forcing to support a cluster of storms,
including the right entrance region of the upper jet, the nose
of a low level jet, and the mid level shortwave trough. With
high cape and marginal shear, wind and hail are the main
threats.

Cronce

&&

.LONG TERM...
Issued 1139 PM CDT Wed Jul 1 2026

Friday through Saturday:

The surface high that was sitting over the southern
Appalachians will gradually weaken and shift toward the Atlantic
coast Friday through the weekend. This breaking down of the
upper ridge will transition us to zonal flow across the Upper
Midwest. Weak ripples (shortwave troughs) in the mid level flow
will help to trigger rounds of thunderstorms Friday through
Saturday night. This is a weather pattern where the timing of
these ripples is uncertain. In addition, the focus of each
consecutive round of storms would likely be along an outflow
boundary from the prior round of storms, so the location is also
uncertain (could end up being in northern IL rather than
southern WI).

For Friday, another shortwave is expected to track across
central or southern WI during the day. With southern WI on the
periphery of the high heat and humidity (instability gradient),
we have a risk for severe storms. The timing and location remain
uncertain.

The heat on Friday is also uncertain, as it will depend on
where that Thursday night outflow boundary rests and ultimately
how much sun we get. It is possible that only a portion (or
none) of southern WI would need a heat advisory.

We have been watching a fairly consistent signal for a robust
shortwave trough to track across WI on Saturday. This would
likely occur during the afternoon at the time of peak daytime
heating, but that is uncertain. The GFS is showing an MCS that
could roll across southern WI Saturday morning, so that could
put a damper on the severity of any storms that develop with the
afternoon shortwave. Again, we will need to wait until the prior
day to get a better handle on timing. I realize this is a
critical time for making decisions about outdoor events and
activities during this Independence Day holiday weekend and it
is frustrating to not have all the information ahead of time.
It is important to have a plan in case of thunderstorms,
including severe.

Sunday through Wednesday:

One more shortwave trough and associated weak surface low is
expected to cross northern WI and Upper Michigan on Sunday.
Higher chances for showers and storms will be closer to this low
to our north, but steep low-mid level lapse rates in this
cyclonic flow will give us scattered shower chances all the way
down to the IL border. This low may take until Monday to clear
the Upper Great Lakes.

A welcomed return of slightly cooler and drier air is slated to
arrive by Monday. The weather should be dry Monday and Tuesday,
but another shortwave trough could bring showers and storms
again by Wednesday. We will still be warm and humid, just not
very hot like it has been.

Cronce

&&

.AVIATION...
Issued 1139 PM CDT Wed Jul 1 2026

VFR conditions expected overall, but MVFR possible in
thunderstorms. Winds will remain out of the south-southwest
through the TAF period. Thunderstorm chances will increase from
northwest to southeast during the overnight hours, with ENW and
JVL having lower chances to see any thunder. See the short term
discussion above for more details. Another round of storms is
looking likely over southern WI Thursday (this) afternoon with
severe storms possible.

Cronce

&&

.MARINE...
Issued 1139 PM CDT Wed Jul 1 2026

High pressure will remain parked over the southern Appalachian
Mountains into the weekend. Meanwhile, a low pressure system
around 29.5 inches will track across Ontario and reach toward
James Bay by Thursday night. Breezy south to southwest winds
will persist through Thursday. Southwest winds will weaken
becoming light Thursday night through Friday. Heading into the
weekend, high pressure in the Appalachian range will gradually
shift east. As the high pressure pulls away, there is a
potential for low pressure to move into the Great Lakes Region
for the weekend.

Chances for thunderstorms (50-60%) remain across the northern half
of the Lake through tonight. Tonight into Thursday morning there is
a small chance (~20%) for rain and storms across the southern half.
The chances for storms (30-60%) will persist from Thursday
afternoon through Friday evening. Additional chances for
rain/storms remains across the entire lake Saturday and Sunday.
Strong to severe storms may occur at times, though confidence
remains low in timing of stronger storms.

Patchy marine fog will be possible at times, primarily over the
northern half of the lake as the warm and moist airmass moves
overhead.

Cronce

&&

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

$$

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