NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 161808
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
108 PM CDT Sun Aug 16 2026

.KEY MESSAGES...

- Scattered thundershowers possible through ~4 PM, particularly
  in far southeast Wisconsin.

- Areas of fog tonight, particularly over the western half of
  the area.

- Showers and thunderstorms return to the forecast Tuesday evening.

- Dry and pleasant conditions Wednesday through Thursday. Rain
  chances return Friday.

&&

.SHORT TERM...
Issued 110 PM CDT Sun Aug 16 2026

This Afternoon through Monday Night:

Synopsis/Mesoanalysis: Surface observations show a cold front
working into southern Wisconsin early this afternoon. While multiple
wind shifts are apparent regionally, the "true" frontal boundary
extends from the Fond du Lac area southwest through Madison, and is
marked by abrupt dew point drops into the mid-60s in the wake of its
passage. With a still humid & modestly unstable air mass in place
ahead of the front, scattered thundershowers remain possible in
southeast Wisconsin prior to the front's mid-afternoon departure.
Apart from a few lightning flashes, hazards aren't expected in any
activity. Currently over the Dakotas, high pressure will build into
the Upper Mississippi Valley tonight, resulting in clearing skies
and weakening winds. Some fog could develop as these conditions
become established after midnight, with potential being highest
across the western half of the area. The high will cross the state
on Monday, bringing seasonable and pleasant conditions. The high
will shift east Monday night as a new area of low pressure builds
into the Northern Plains, allowing winds to turn southwesterly
regionally. The wind shift will gradually bring more humid air back
into southern Wisconsin, with an isolated thunderstorm possible
closer to daybreak Tuesday.

This Afternoon: Will be monitoring the progress of the cold front &
any thundershower development along it through 4 PM. Highest near-
term thundershower potential will reside within a band of agitated
cumulus clouds & radar returns moving east from the Madison area,
though additional development will be possible as the front impinges
upon a still muggy air mass in southeast Wisconsin. Shower depths
have remained largely below the -10C level over the last hour, which
has resulted in no lightning in any activity developing thus far.
Nevertheless, a few taller showers capable of a couple lightning
flashes can't be entirely ruled out given the instability still
available over southeast Wisconsin. Move indoors if any thunder
approaches your location.

Quigley

&&

.LONG TERM...
Issued 110 PM CDT Sun Aug 16 2026

Tuesday through Sunday:

Synopsis: Moisture will continue to work back into southern
Wisconsin Tuesday, leading to muggier conditions. A cold front will
swing through the western Great Lakes Tuesday evening into
Wednesday, triggering the next round of shower and thunderstorm
development. Tuesday evening & night continues to be most favored
for storms in southern Wisconsin. Broader ingredients will be in
place for a few stronger storms with heavy downpours, though trends
continue to be monitored for more precise placement & intensity
details. The cold front is forecast to be south of the Wisconsin-
Illinois border by Wednesday morning, with drier northerly flow &
passing high pressure leading to pleasant & precip-free conditions
Wednesday afternoon through Thursday. Winds will trend southwesterly
on Friday, bringing milder and modestly more humid air to the
region. The next cold front is forecast to move through the western
Great Lakes Friday evening, when some scattered showers and
thunderstorms will be possible. Pleasant conditions will return by
the Saturday-Sunday time frame behind the departed front.

Tuesday Evening: Continue to anticipate a window for scattered
showers and storms between ~3 PM & Midnight along the approaching
cold front. Broad setup details---particularly forcing from the
front, relatively favorable arrival timing of the frontal forcing,
and sufficient wind shear---point toward an environment generally
favorable for more organized storm development in southern
Wisconsin. The limiting factor, however, remains the quality of
moisture return (& thus instability) ahead of the encroaching
front/on the back side of departing high pressure. With a source
region centered well to the west over South Dakota/Nebraska,
returning moisture will be racing the cold front to southern
Wisconsin, with any combination of a faster frontal speed and/or
slower-departing high impeding its progress. This will be the main
trend being monitored over the next 24-36 hours. A stronger storm
with gusty winds would be possible wherever the deepest (65+ degF)
moisture returns can establish, with current guidance suggesting the
greatest potential from Madison & points southwest. Seasonably moist
conditions will support heavy downpours in any storms, though
flooding potential would be low in the absence of any training.

Quigley

&&

.AVIATION...
Issued 110 PM CDT Sun Aug 16 2026

A mix of MVFR and VFR flight categories prevails along/ahead of an
approaching cold front this afternoon. General trend has been for
greater MVFR coverage in the southeast half of the area, where pre-
frontal moisture remains a touch deeper. VFR is becoming more
prevalent across the northwest as drier air gradually works in with
and behind the front. Have adjusted near-term forecasts to upstream
observational conditions at each terminal in the 18Z update, with
the expectation of a full return to VFR categories by mid-afternoon.
West-northwest winds will be breezy as the front works through. Will
be monitoring for widely scattered SHRA and TSRA along the passing
front, particularly in southeast Wisconsin. Confidence in
development and placement of precip is too low to justify any
mentions in the 18Z forecast, but will be planning to add TEMPO
and/or brief prevailing groups if trends dictate. Precip potential
concludes by early evening, with skies clearing & winds lightening
tonight.

Quigley

&&

.MARINE...
Issued 110 PM CDT Sun Aug 16 2026

A cold front is approaching the open waters of Lake Michigan this
afternoon, resulting in breezy west-northwest winds. These
conditions will continue into this evening as the front clears east
of the waters. A scattered shower or thunderstorm is possible along
the departing boundary, particularly over the southern third of the
waters. Severe weather is not anticipated.

A new area of 1018 mb high pressure will build in from the northern
Great Plains late tonight into Monday, bringing light and variable
winds to the waters through the majority of Monday and Monday night.
A slow-moving cold front will approach from the northern Great
Plains Tuesday into Wednesday, bringing increasing southwest winds
and chances for thunderstorms. Tuesday evening and night appears
most favored for storm potential, with storm chances expected to
move well south of the waters on Wednesday. 1016 mb high pressure
will move through the western Great Lakes Wednesday through
Thursday, with light and variable winds prevailing across the
waters. The next thunderstorm chances arrive Friday afternoon and
evening, when the next cold front is expected to move across Lake
Michigan.

Small Craft Advisory conditions are not anticipated through this
week in nearshore zones. Scattered showers and thunderstorms are
possible along a passing cold front this afternoon. Additional
shower and thunderstorm chances are forecast Tuesday evening/night,
as well as on Friday afternoon & evening.

Quigley

&&

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

$$

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