NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 161108 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
608 AM CDT Tue Jun 16 2026

.KEY MESSAGES...

- Showers (45-65 percent chance) and scattered thunderstorms
  this afternoon. Small hail expected with the thunderstorms.

- Widespread showers (80-90 percent chance) and scattered
  thunderstorms Wednesday and Wednesday night. Heavy rain and a
  conditional threat for severe thunderstorms is forecast.

- Winds and waves may approach Small Craft Advisory criteria
  Wednesday afternoon into Thursday.

- Next noteworthy chance for thunderstorms is Sunday.

&&

.UPDATE...
Issued 608 AM CDT Tue Jun 16 2026

The initial line of showers associated with warm advection
ahead of the approaching trough will continue eastward across
the eastern forecast area early this morning. After at least
partial clearing behind these showers, clouds will move back in
by late morning as the trough pushes in from the northwest.
Additionally, scattered showers will accompany the trough, with
some thunder possible by early afternoon with the trough axis
overhead. Still think some small hail will be possible with any
afternoon storms. Bumped temps down a bit in the northwest given
the small window of opportunity for sunny skies ahead of the
trough. Otherwise, the forecast looks on track for the upcoming
day.

DDV

&&

.SHORT TERM...
Issued 100 AM CDT Tue Jun 16 2026

Today through Wednesday night:

Through the predawn hours today, a compact shortwave is expected
to track southeast from MN into northwest WI, inducing a narrow
LLJ over eastern IA and southern WI. The associated WAA may
develop some widely scattered rainshowers (or even weak
thunderstorms) in the region between roughly 3 AM and 9 AM this
morning. A lull in the shower activity would then be likely
late this morning as this activity pushes east over Lake
Michigan.

The shortwave trough closes off into a compact upper low over
central portions of WI throughout the day today, slowly tracking
east. The relatively cool air aloft, preexisting modest mid-level
lapse rates, and sharpening low-level lapse rates (through the
course of daytime heating) should allow this feature to produce a
second round of showers and thunderstorms this afternoon
(Noon-7PM), this time with greater coverage. The relatively low
freezing levels (beneath 8,000 ft at times) should allow any
thunderstorm cells to produce small hail. Dry weather returns
this evening.

As another 500mb trough tracks southeastward across the Dakotas
tonight, diffluent flow overspreads Iowa and an MCS evolves. 00z
model guidance depicts this MCS tracking eastward into southern
WI and much of IL, arriving between 5-9 AM Wednesday morning.
With HREF Mean MUCAPE under 1,000 joules in our region and
substantially higher into IA/IL, it would appear that the
majority of the stronger / severe storms will dive south of our
region, leaving sub-severe storms (still plenty capable of
lightning and possibly brief heavy rainfall) to overspread our
region Wednesday morning.

Deep surface low pressure behind the MCS will then attempt to
draw the effective warm front (and instability plume) northward
into far southern WI Wednesday afternoon. The 00z HREF's best
guess is that the warm front will setup just south of the WI/IL
border and shield us from surface based convection (and thus
reduce severe wx potential), but as stated during the prior
forecast iteration, a small shift in the MCS or low pressure
system track could still bring the warm front as far north as
southern WI, yielding an all-hazards severe threat south of the
I-94 corridor. Stay tuned to this forecast, as details can and
will change.

Sheppard

&&

.LONG TERM...
Issued 100 AM CDT Tue Jun 16 2026

Thursday through Monday:

Predominantly dry weather expected in the cool sector of the
departing low pressure on Thursday. Some lingering 500mb vorticity
on the north edge of the jet, some cool air aloft, and steepening
low-level lapse rates through the course of diurnal heating (below
the subsidence inversion) allows models to yield some low chances
of cellular rain showers Thursday (~10-15% chance). A similar
story for Friday, not enough jet dynamics to support much else.
Ensemble plots for High Temps suggest a daytime high around 70 /
low 70s for Thursday, with only a very slight overall warming
trend this weekend into early next week (ensemble mean high
temps centered in the mid 70s, with growing dispersion).

For Saturday, the longwave trough axis centered over our region
begins to exit east (hence the slight warming trend). Warm/moist
return flow over the Great Plains sets up a NW to SE oriented
baroclinic zone from southern MN into eastern IA / northwest IL
(and perhaps southern WI), which leaves the potential for a
ridge-riding shortwave to kick-off an MCS Friday night and track
it along that gradient towards our region Saturday morning. The
models (for now) suggest that the gradient and MCS (as seen in QPF
output) will setup southwest of us, though we have some 20-30%
precip chances across our CWA just in case.

Our next noteworthy chance for thunderstorms arrives Sunday, with
plenty of uncertainty as to how things will shake out. Multiple
ECMWF Ensemble Members track an organized low pressure system
northeast from the Central Plains towards southern WI (a setup
which would leave organized thunderstorm chances on the table),
whereas several GEFS members track the low through Illinois,
leaving us with no southerly return flow. A large subset of
members from each modeling system stalls the low over the Central
Plains, leaving the baroclinic zone northeast of it and any
corresponding satellite low pressure to attempt a northward push
of moisture / QPF into our region. All this to say the
predictability is very low, but there are chances for showers
and thunderstorms Sunday.

Sheppard

&&

.AVIATION...
Issued 608 AM CDT Tue Jun 16 2026

Scattered showers across the east early this morning will be
followed by a brief break in clouds and precip ahead of an
approaching trough. Showers will move back in from the northwest
mid to late morning along with mostly cloudy skies. Ceilings may
briefly drop to MVFR as the trough arrives, mainly northwest of
Madison. Scattered showers will then progress across the
forecast area late morning into the afternoon, with some thunder
and small hail also possible by afternoon.

Dry weather this evening into at least early tonight will give
way to increasing chances for showers late tonight into
Wednesday as the next trough approaches. More widespread precip
and lower clouds are expected with the system tomorrow.

DDV

&&

.MARINE...
Issued 100 AM CDT Tue Jun 16 2026

Southwesterly winds shift southerly early this morning as a low
pressure system deepens over northern Lake Michigan (29.5
inches). Winds become relatively light and variable underneath
it (northern half of the lake) later this afternoon, with winds
veering west over the southern half. Showers and thunderstorms
will be possible across the lake through the daytime hours
today, a couple of stronger cells this afternoon could produce
small hail.

A weak surface ridge crosses the lake tonight, with winds
subsiding and backing southwest. A much more organized low
pressure system (29.2 inches) will then track eastward from
around South Dakota, crossing Lake Michigan Wednesday evening.
Ahead of it's arrival, we expect gusty southeast winds Wednesday
morning and afternoon (particularly over the southern half of
the lake) with increasing chances for thunderstorms, some of
which could be strong (particularly over far southern portions
of the lake). Breezy west to northwest winds are expected
Wednesday night into Thursday as the low exits east. This same
breeze then continues into Friday (albeit weaker) as weak high
pressure builds into the region from the west.

Sheppard

&&

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

$$

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