NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 302310
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
610 PM CDT Sun Aug 30 2026

.KEY MESSAGES...

- Building heat and humidity through midweek. Heat index values
  near 100 degrees possible across far southern Wisconsin
  Tuesday and Wednesday.

- Rain & scattered storms continue through tonight. Severe
  weather isn't expected in any activity.

- Storm chances (~15%) return Monday afternoon along a weak cold
  front. A few of these storms may become severe, if they
  develop.

- Uncertainty remains in timing and intensity of storms Monday
  night through the end of the week as an active pattern remains
  over the Great Lakes region.

&&

.UPDATE...
Issued 615 PM CDT Sun Aug 30 2026

Afternoon showers and storms have largely pushed out over Lake
Michigan, with a new area of shower & sporadic thunder
development currently ongoing to the west of Madison. Said
activity has blossomed within a band of warm advection rooted in
the 925-700 mb layer. The deep warm advection has allowed
activity to persist eastward despite markedly lower MUCAPE in a
worked over environment in southern Wisconsin. Whether this
trend will continue remains uncertain, particularly if the
precip becomes separated from the warm advection sustaining it.
Have nevertheless upped near-term precip probabilities areawide,
with the highest (~60%+) values in place along/west of I-39
where confidence in rainfall is highest. Filled ~25-40% values
in further east given the remaining questions regarding precip
longevity. Should activity continue to hold together, will plan
to up precip probs by mid-evening. Apart from a few flashes of
lightning, not anticipating any hazards in this additional
precip activity.

Quigley

&&

.SHORT TERM...
Issued 341 PM CDT Sun Aug 30 2026

Tonight through Monday night:

Scattered thunderstorms early this afternoon have generally
merged into a single area of widespread rainfall, which will
gradually propagate eastward into Lake Michigan by sunset.
Overnight, stiff southwesterly winds will develop between 850
and 500 mb, allowing for MUCAPE ~500 J/kg to build across the
region and scattered storms to develop after midnight into the
morning hours. These storms will gradually slide southeastward
into midday Monday as low pressure finally propagates
southeastward into southern Minnesota. A weak cold front with
this system will serve as the focal point for the next round of
potential storms on Monday afternoon, but the intensity of this
round is dependent on how late in the day the morning round
lingers (i.e., how much the capping inversion can whittle away
after morning precipitation ends). If storms do develop in the
afternoon hours, they would be capable of producing small hail
and gusty winds with inverted V soundings and MUCAPE building
back into the 1500 J/kg realm. 0-6 km shear 35-40 kt will allow
for updrafts to sustain themselves if the cap can be broken. A
Marginal risk (1/5) is in effect for southwestern to central
Wisconsin for these concerns.

Overnight Monday into Tuesday, uncertainty develops with timing
and placement of storms, as ridging shifts southward and the
parent low lifts northward. Isolated to scattered storms are
still possible, but not likely at this time (15-20% chances).

MH

&&

.LONG TERM...
Issued 341 PM CDT Sun Aug 30 2026

Tuesday through Sunday:

Heat and humidity builds across southern Wisconsin Tuesday, with
heat index values in the mid to upper 90s expected. Highest
temperatures are expected near the WI/IL border, and a few spots
may break 100 degree heat index values with temperatures in the
upper 80s. However, overrunning precipitation from the previous
night, should it develop, could temper these high temperatures
and prevent Heat Advisory criteria from being met. Southwesterly
winds will allow for heat to make it all the way to Lake
Michigan, although afternoon lake breeze influence may offer
some relief. Overnight Tuesday, LLJ dynamics return to the area,
with widespread precipitation possible in the WAA region across
central Wisconsin to northern Iowa. If this precipitation is
able to form a cold pool, severe weather would become possible
as an MCS moves eastward through the mean flow. Kept NBM PoPs of
20-40%.

Isolated storms may linger into Wednesday, but with building
ridging not anticipating significant impacts. The more impactful
story at this point will be the heat index values in the upper
90s to potentially 100 degrees near the IL border where air
temperatures reach 90 degrees. Cloud cover remaining across
central WI will keep heat concerns lower, with indices near 90
degrees and temperatures in the mid-80s. Wednesday night, LLJ
focuses on central Iowa, which indicates a decaying MCS may
move eastward through southern Wisconsin into Thursday morning.
Going through the rest of the workweek, continued periods of
on-and-off thunderstorms are expected as southern Wisconsin
remains along the northern edge of ridging across the Southeast
and Mississippi Valley regions. Exact details will be refined as
events approach.

Pattern looks to dry out into next weekend as a drier airmass
from northeastern Canada works its way southward into the Great
Lakes region.

MH

&&

.AVIATION...
Issued 615 PM CDT Sun Aug 30 2026

Predominantly VFR flight categories have re-established early
this evening in the wake of afternoon showers and thunderstorms.
Monitoring an additional area of showers & embedded thunder
development to the west of Madison, which is expected to persist
toward the I-39 Corridor through the near-term. Have accounted
for these expectations with prevailing -RA groups at MSN and JVL
in recent updates & the coming 00Z forecast. Whether precip is
able to maintain into southeast Wisconsin later in the evening
remains uncertain, with forecast confidence too low to justify
prevailing or TEMPO groups in the coming 00Z forecast. Have thus
carried PROB30 -RA groups at all eastern terminals for several
hours during the mid-evening, and will plan to amend as radar
trends dictate. Upstream observations suggest that VFR flight
categories will persist through the majority of any additional
precip, though brief periods of MVFR VIS reductions can't be
completely ruled out. Have accounted for this potential with
TEMPO groups at MSN and JVL, and have refrained from any such
mentions further east given lower confidence in the persistence
of rain.

Quigley

&&

.MARINE...
Issued 341 PM CDT Sun Aug 30 2026

Breezy southerly winds will gradually diminish tonight as high
pressure of 30.1 inches moves south into the Appalachians and low
pressure of 29.7 inches lifts into the Canadian Prairies and
deepens to 29.5 inches. A Small Craft Advisory remains in effect
for nearshore regions of southern Wisconsin through this evening
for continued gusty southwest winds and elevated waves. Southwesterly
winds are expected to continue through Tuesday as low pressure
continues to dominate the pattern and slowly moves east through
Canada. Expecting scattered thunderstorms on- and-off through
the end of the week as a weak front lingers across the region.
The front will finally sink southward Wednesday into Thursday,
with light northerly winds eventually taking hold.

MH

&&

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

$$

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