NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 010121 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
821 PM CDT Tue Jun 30 2026

.KEY MESSAGES...

- An Extreme Heat Warning remains in effect for all of southern
  Wisconsin through early Wednesday evening. Additional heat
  headlines may be needed for the second half of the week, but
  some uncertainty remains due to clouds and rain chances.

- Thunderstorm chances return tonight through the end of the
  week, as the hot and humid pattern continues. There are
  chances for storms tonight, mainly along and north of a line
  from Lone Rock to Fond du Lac.

- Increasing chances for storms are forecast Wednesday into the
  holiday weekend on a more areawide basis. Strong to severe
  storms may occur at times, though confidence remains low on
  the timing of each round of storms.

&&

.UPDATE...
Issued 821 PM CDT Tue Jun 30 2026

The Extreme Heat Warning will remain in effect until 7 PM CDT
Wednesday evening. An extension or a Heat Advisory issuance
into later in the week may eventually be needed, depending on
how many clouds and showers/storms occur. Will likely wait on
how clouds and possible shower/storm trends play out overnight
into Wednesday before making further decisions on the heat
headlines for the rest of the week.

A few storms are possible this evening northwest of Madison,
closer to the axis of the low level jet and warm air/moisture
advection. There is a better chance for showers and storms
developing later this evening into the overnight hours, perhaps
lingering into early Wednesday morning before pushing
northeastward. The southwesterly low level jet will be the key
feature to watch, as it develops more of a nose and shifts
northeastward toward the area.

CAMs are all over the place with some having unrealistic
depictions of storm propagation. Given the setup with the
southwesterly flow through a deep layer focused from Iowa into
southwest and central Wisconsin, would expect any showers and
storms that develop with the low level jet nose to push
northeast and ride the ridge through these areas.

Thus, far western, northwestern and far northern portions of
the area may see chances (20 to 40 percent, highest northwest)
for showers and storms overnight into early Wednesday morning.
There is a good amount of elevated CAPE (2000 to 3000 J/kg),
with weaker deep layer bulk shear around 20 knots increasing to
30 to 35 knots. Thus, any stronger storm could produce hail,
gusty winds and locally heavy rainfall, given the very moist
airmass in place and storms possibly moving over the same areas.

Wood

&&

.SHORT TERM...
Issued 255 PM CDT Tue Jun 30 2026

Tonight through Wednesday night:

Hot and humid conditions continue into tonight with heat index
values remaining in the 100 to 105 range. Tonight, heat will
remain a concern, as overnight lows will only drop into the mid
to upper 70s.

The ridge held fast through today keeping storm activity north
of the area, but tonight, models depict some storm activity over
central increasing through the overnight hours as the
environment uncaps and the LLJ kicks off convection. Storm
motion vectors would carry any storms over central WI to the
northeast sparing most of the area, but areas north of a line
from Lone Rock to Fond du Lac may see a glancing blow from
thunderstorm activity. Given the steep mid level lapse rates,
large hail may occur with any storms, and there may be some wet
microburst potential give the high PWATs and low shear. This
activity would move through just before and just after dawn on
Wednesday.

After morning thunderstorm activity, more hot and humid
conditions are expected with highs in the low to mid 90s, with
heat indices above 100.

CMiller

&&

.LONG TERM...
Issued 256 CDT Tue Jun 30 2026

Thursday through Tuesday:

The upper level ridge begins to flatten Thursday allowing more
thunderstorm activity into the area. There looks to be some
potential for a morning round, followed by a late afternoon and
evening round. The latter round may feature more of the severe
threat, given the potential for instability to build through
Thursday.

Beyond, the ridge sinks southward, allowing a more favorable
band of flow aloft to pass over the area into the weekend. Daily
thunderstorm chances look possible, but each days chances will
be highly dependent upon where the previous day's rounds of
storms force an outflow boundary to flow and act as a storm
trigger. As such a high amount of uncertainty will linger into
the 4th of July weekend regarding storm timing/position.

Hot and humid conditions will linger through Friday. with highs
near or into the 90s. Temps "cool" this weekend with highs in
the 80s, but dewpoints will remain elevated into next week,
prolonging the mugginess.

CMiller

&&

.AVIATION...
Issued 821 PM CDT Tue Jun 30 2026

Gusty southwest winds early this evening will weaken by later
this evening and overnight. Gusty southwest winds should return
Wednesday by midday into the afternoon and early evening.
Removed mention of low level wind shear in TAFs for now, as
surface winds should remain high enough to limit this potential.

There may be broken ceilings around 5000 feet AGL later this
evening into early Wednesday morning for areas west and north of
Madison to Fond du Lac, if some showers and storms develop. Most
terminals to the southeast of here should remain dry and may not
see much in the way of clouds during this time. Locally reduced
ceilings and visibilities may occur in any showers and storms.

Wood

&&

.MARINE...
Issued 821 PM CDT Tue Jun 30 2026

A Small Craft Advisory continues until 10 PM CDT this evening,
for gusty southwest winds and building waves. Modest to breezy
southerly winds will prevail into Thursday, then lighter into
Friday as high pressure remains to the southeast of the Great
Lakes. Troughs of low pressure will continue over Canada into
the northern Great Plains.

Thunderstorms will continue to move east across central
portions of the lake early this evening. There are mainly small
chances for additional thunderstorms later this evening and
overnight. Chances for thunderstorms are forecast across the
northern half of the lake through Wednesday night. There are
chances for thunderstorms across the southern two thirds of the
lake Thursday into Friday evening, and across the southern half
of the lake later Friday night into Sunday, as a cold front
shifts winds to northerly.

Some strong to severe storms may occur at times, though
confidence remains low with the timing of each round of storms.
Patchy marine fog will be possible at times, primarily over the
northern half of the lake, as a warm moist air mass moves over
the lake.

CMiller/Wood

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory...LMZ643-LMZ644-LMZ645-LMZ646 until 10 PM
     Tuesday.

&&

$$

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