NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 180144 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
844 PM CDT Mon Aug 17 2026

.KEY MESSAGES...

- Showers and storms return Tuesday. Currently favored window
  for precip is 1-9 PM. An isolated severe storm with hail and
  gusty winds can't be ruled out.

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

- Nice weather expected this weekend.

&&

.UPDATE...
Issued 845 PM CDT Mon Aug 17 2026

Mid level clouds will spread into southern WI late tonight/early
Tuesday morning as areas of diminishing thunderstorms approach
from MN and IA. These diminishing storms are the ones currently
over MN and are developing along the nose of the low level jet
(LLJ). As the LLJ weakens in the morning, so will the storms.

It looks like some remnant light showers could trek across
southern WI along a slow-moving front from midday through mid
afternoon. Southern WI will be in a zone of 850mb warm
air/moisture advection during this time. While there could be a
few storms with this feature, the better chance for storms
should be along any remnant outflow boundary during the late
afternoon and early evening. This is the time period when
another shortwave will be tracking across southern WI (currently
this is the feature that is triggering storms in southeast
Montana).

Any storms will be widely scattered and brief but would have
gusty winds and heavy downpours. Several meso models are showing
an east-west outflow boundary where storms would develop. The
favored position for this is in northern IL. Wherever this sets
up, it would come with a risk for training storms and heavy
rain.

Cronce

&&

.SHORT TERM...
Issued 225 PM CDT Mon Aug 17 2026

This Afternoon through Tuesday Night:

Synopsis/Mesoanalysis: A ridge of surface high pressure is moving
into Wisconsin this afternoon, resulting in mainly west-northwest
winds across the region. Lone exception to the broader pattern is
near Lake Michigan, where a lake breeze is attempting to mix inland.
Expect the lake breeze to continue nudging west into the afternoon,
with an easterly wind shift and slightly cooler temperatures
materializing in its wake. Further west, surface observations show a
cold front extending from Grand Forks, North Dakota southwest into
the South Dakota Black Hills. The boundary will work toward the
Upper Mississippi Valley tonight, and is forecast to pull through
southern Wisconsin Tuesday afternoon & evening. Shower and
thunderstorm chances return along/ahead of the boundary, with peak
potential between ~1-9 PM Tuesday. While not expected to be
widespread, a few strong-severe thunderstorms with gusty winds and
damaging winds can't be ruled out. Heavy downpours will also
accompany thunderstorms, with widespread flooding potential
appearing low at this time. Conditions will dry out Tuesday night as
the cold front departs & drier air begins to work into the area.

Tonight-Tuesday Morning: With high pressure influences lingering,
can't rule out some fog in the Wisconsin Valley. Not anticipating
any dense fog, but will be monitoring visibilities. Will also be
watching radar trends from the Northern Plains into the Upper
Mississippi Valley. Expecting areas of thunderstorm development
across this region as warm/moist advection commences ahead of the
encroaching cold front. Relatively solid consensus amongst high-res
guidance points to this activity remaining west of the region
through the overnight hours, though individual solutions begin to
diverge regarding the eastward continuation of activity beyond
daybreak. This divergence leads to several possible scenarios
regarding shower/storm potential over the area on Tuesday morning,
with possibilities ranging from entirely dry conditions to areas of
showers/storms moving in from the west. With residual drier air
still in place on the back side of departing high pressure/the bulk
of moisture recovery having yet to occur locally, have trended the
forecast toward the quieter/less precip scenario in the afternoon
update, but will need to closely monitor for possible increases in
precip probs into tonight. Not expecting any severe weather hazards
in the event showers/storms make it into the region Tuesday morning
given little or weak instability.

Tuesday Afternoon-Evening: The currently favored window for showers
and storms opens as the cold front moves through. ~1-9 PM being the
preferred window for storms will be heavily contingent on sufficient
moisture & instability recovery in southern Wisconsin during the
morning hours, with any combination of storms to the west/over the
area or affiliated cloud debris acting to disrupt the
destabilization process. Given current thinking (namely that
conditions will stay drier during the morning & that some
destabilization will be able to occur), have thus brought
~60%/likely precip probabilities into the forecast during this time
frame, with the understanding that changes could occur in the event
that the morning plays out differently. Given that some
moisture/instability recovery would have occurred in this scenario,
overlapping wind shear would be sufficient for a few organized
storms capable of gusty winds & isolated large hail. Level 1/5
severe weather risk thus continues across most of southern Wisconsin
in the latest severe outlook from the Storm Prediction Center. Stay
weather-aware if planning to be outdoors Tuesday afternoon/evening.

Quigley

&&

.LONG TERM...
Issued 225 PM CDT Mon Aug 17 2026

Wednesday through Monday:

Synopsis: The cold front responsible for Tuesdays storm potential 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. High pressure will slide through the
western Great Lakes Sunday into Monday, maintaining pleasant
conditions through the conclusion of the long term period.

Friday Afternoon-Evening: Appears that the next window for showers &
thunderstorms will open along the next cold front. Similar to
Tuesdays setup, a combination of abundant synoptic forcing +
sufficient wind shear points toward general favorability for more
organized thunderstorms, with pre-frontal moisture return &
instability being the limiting factor on more precise storm
coverage, location, and intensity. Will be monitoring trends
regarding these factors over coming forecasts & providing additional
updates as details clarify.

Quigley

&&

.AVIATION...
Issued 845 PM CDT Mon Aug 17 2026

Mid level clouds will spread into southern WI early Tuesday
morning as areas of diminishing thunderstorms approach from MN
and IA. It looks like light showers could trek across southern
WI from midday through mid afternoon and this is reflected in
the TAFs. While there is a chance of storms in the TAF from
18-20Z (south central WI) or 19-21Z (SE WI), I am not confident
in them developing within that timeframe. The other window that
they could develop is between 22Z and 02Z. Any storms will be
widely scattered and brief but would have gusty winds and heavy
downpours.

Cronce

&&

.MARINE...
Issued 225 PM CDT Mon Aug 17 2026

1018 mb low pressure is approaching Lake Michigan this afternoon,
bringing light to variable winds to the open waters. The lighter
winds will continue into this evening as the high continues east. 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. An isolated stronger storm
with gusty winds cant be ruled out in this activity, though
widespread severe weather potential appears low at this time. Will
continue to monitor trends through tomorrow. 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 aren't expected through this week in
nearshore zones. Showers and thunderstorms are possible Tuesday
evening and Friday afternoon along a pair of cold fronts. Widespread
severe weather isn't expected in either window of activity, though
an isolated stronger storm with gusty winds can't be ruled out on
Tuesday evening. Will continue to monitor trends and provide
additional updates through tomorrow.

Quigley

&&

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

$$

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