NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 111832
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
132 PM CDT Fri Sep 11 2026

.KEY MESSAGES...

- Moderate swim risk this afternoon at Sheboygan County beaches.

- A few light sprinkles or showers possible early Saturday
  morning across the west. No hazards expected.

- Active start to next week, with multiple periods of showers & storms
  expected Monday evening through at least Tuesday. Some storms
  could produce locally heavy rainfall and gusty winds.

&&

.SHORT TERM...
Issued 135 PM CDT Fri Sep 11 2026

Rest of this Afternoon through Sunday night:

Synopsis/Mesoanalysis: High pressure is centered over southern
Ontario early this afternoon, allowing southerly winds to become re-
established across southern Wisconsin. Aided by onshore synoptic
flow, a weak lake breeze has established itself near the Lake
Michigan shoreline, providing just enough lift for fair weather
cumulus. Expect fair weather cumulus to broaden in coverage as
surface heating and modest moisture returns continue through late
afternoon. Well west of the region, surface obs show an area of
deepening low pressure near Aberdeen, South Dakota. The surface low
will continue to track toward the Minnesota-Ontario border through
tonight, gradually pulling a cold front into the Upper Mississippi
Valley in the process. The front will trigger thunderstorm
development over north-central Minnesota this evening, with activity
attempting to work toward the area during the predawn hours.
Anticipate that the bulk of showers & storms will weaken before
reaching southern Wisconsin, though an isolated shower or sprinkle
can't be ruled out to the west of I-39. The front will progress
across the area Saturday afternoon, with a dry frontal passage
anticipated at this time. Winds will trend northwesterly behind the
departed front Saturday evening, bringing a cooler & drier air mass
for Sunday. Will be watching for a few pop-up showers during the day
Sunday, though confidence in development is low at this time.

Rest of this Afternoon: Building waves to three feet will lead a
moderate swimming risk at Sheboygan County beaches between ~1-7 PM.
Exercise extreme caution if heading lakeside, and avoid dangerous
areas like breakwaters and piers if planning to get into the water.

Tonight through Saturday Afternoon: Will be monitoring trends for
isolated showers along the approaching cold front. Thinking that the
best potential will be late tonight to the west of I-39 as pre-
existing precip weakens on approach to the region. Activity will in
all likelihood struggle to make it further east given weakening
convergence in the vicinity of the front. Expect the aforementioned
lack of frontal convergence to remain a factor through Saturday as
the front crosses the area, which has motivated a dry forecast
through the daytime hours. Will continue to watch for possible
adjustments to precip probabilities through tonight.

Sunday: Expecting pleasant, early fall-like temps & humidity. Have
maintained slight chance (~15-30%) precip probabilities during the
daytime hours given an upper disturbance moving in from the west.
Whether lift from the disturbance will be able to overcome dry air
settling into the lower levels remains uncertain, with trends being
monitored for possible precip prob reductions in coming forecasts.

Quigley

&&

.LONG TERM...
Issued 135 PM CDT Fri Sep 11 2026

Monday through Friday:

Synopsis: High pressure will shift toward Ontario & the Saint
Lawrence Valley Monday afternoon & evening, allowing southerly winds
& warm/moist advection to commence areawide. An upper trough will
concurrently advance toward the Lake Superior vicinity, with
attendant surface cyclogenesis near Lake Winnipeg further
reinforcing the southerly return flow & warm advection. The
developing surface low will pull a cold front into the western Great
Lakes Monday night into Tuesday, with the boundary stalling near or
south of the Wisconsin-Illinois border through the mid-week time
frame. Between the amplifying warm/moist advection & encroaching
surface front, additional periods of showers and storms are thus
expected from Monday night into at least Tuesday. Whether or not
precip chances will linger into Wednesday will depend on the
stalling location of the passing surface front, with a number of
different solutions apparent in current forecast guidance. Some
storms---particularly those occurring Monday night & Tuesday---could
be stronger with locally heavy rainfall. The next area of high
pressure will arrive by Thursday, bringing quieter and seasonable
conditions for the end of next week.

Monday Evening & Night: Shower and storm chances increase areawide
given an abundance of arriving large scale forcing. Given the
synoptics in play, confidence is high in the occurrence of
widespread showers and storms, with the 50-80%+ precip probabilities
from current NBM guidance appearing more than reasonable. What
remains less certain is the hazards potential---particularly locally
heavy rainfall & damaging wind gusts---that will accompany the
expected storms. Materialization of hazards will reside in the
placement & arrival timing of the unseasonably moist & modestly
unstable air mass being ushered in by southerly return flow.
Abundant deep layer shear on the order of 40+ kts will overlap with
this air mass, supporting at least some potential for organized
storms capable of gusty winds. How far this air mass gets & how
quickly it does so will depend on the relative strengths of
departing high pressure & the surface low forming near Lake
Winnipeg. Any combination of stronger high pressure and/or weaker
low pressure would result in a slower-arriving favorable air mass
confined to more western parts of the area. Opposite combinations of
high & low strengths would conversely allow favorable thermodynamics
to arrive over more of southern Wisconsin in shorter order. Air mass
recovery & its relation to evolving surface features will thus be
the primary trend to monitor into this weekend. Current forecast
thinking favors that of a more western solution, with the
understanding that additional shifts are possible as additional
forecast guidance arrives through the weekend. Will continue to
provide updates in coming forecasts.

Tuesday: Depending on where the primary cold front ends up in the
wake of Monday night precip, could see more shower & storm
development with additional locally heavy rainfall potential. Have
trended likely (~60+%) precip probabilities toward the currently-
favored position of the cold frontal boundary, which would place
areas near/south of I-94 & US-18 in line for the best chances of
additional storm development. Anticipate additional shifts in
preferred corridors for storm redevelopment, with trends being
monitored over coming updates.

Quigley

&&

.AVIATION...
Issued 135 PM CDT Fri Sep 11 2026

Predominantly VFR flight categories prevail through the period at
all terminals. A southerly wind shift will continue to establish
itself through the remainder of this afternoon as high pressure
shifts east of the area. The southerly winds will continue into
tonight as low pressure shifts from the Dakotas into northern
Minnesota. A cold front will move into the Upper Mississippi Valley
tonight, approaching western areas by sunrise. An isolated shower
can't be ruled out along the approaching front, though confidence is
too low for any mentions at this time. Will be monitoring radar
trends into tonight for any potential amendments. Aforementioned
cold front will move across southern Wisconsin during the day
Saturday, bringing a northwest wind shift to all aerodromes by mid-
afternoon. Not currently expecting any precip as the boundary moves
through.

Quigley

&&

.MARINE...
Issued 135 PM CDT Fri Sep 11 2026

1017 mb high pressure is shifting into southern Ontario this
afternoon, allowing winds to shift generally southerly across the
open waters of Lake Michigan. Southerly winds will continue to
increase into tonight as 996 mb low pressure moves from the northern
Great Plains toward the US-Canadian border. Winds will shift out of
the west-northwest during the day Saturday as a cold front moves
across the lake. Expecting wind gusts to remain primarily in the 25-
30 knot range from this evening through Saturday, though occasional
gusts approaching gale thresholds can't be completely ruled out.
Currently anticipating any such gusts to remain brief and isolated
enough to preclude the need for Gale Warnings, but will continue to
monitor trends. Isolated showers and thunderstorms are possible
ahead of the approaching cold front, with severe weather hazards not
expected.

1024 mb high pressure will build in from the northern Great Plains
Sunday night into Monday, bringing decreasing winds Saturday night
through Sunday & light/variable winds Sunday night into Monday. The
high will move east of the waters Monday afternoon & evening,
resulting in a south-southeast wind shift. Winds will increase
further & veer south-southwesterly Monday night into Tuesday as 996
mb low pressure develops over Manitoba. Gales continue to appear
likely during this time frame, with headlines becoming necessary in
later forecasts if trends continue to hold. Periods of showers and
thunderstorms will accompany the developing low from as early as
Monday evening through at least Tuesday afternoon. Widespread severe
weather hazards appear low over Lake Michigan at this time, though
an isolated stronger storm with gusty winds can't be entirely ruled
out. Winds will trend northerly behind a cold front Tuesday night
into Wednesday, steadily tapering away from gale thresholds in the
process.

Winds and waves will come up this afternoon as high pressure moves
east and low pressure develops over the Northern Plains. A Small
Craft Advisory is now in effect between 1-7 PM CDT from Port
Washington north to Sheboygan, where the highest winds and waves are
anticipated. Conditions will taper as winds shift offshore this
evening. A brief (~3 hours) period of additional Small Craft
Advisory gusts is possible Saturday afternoon along a passing cold
front, though conditions are expected to remain brief & isolated
enough to preclude the need for additional headlines. Additional
Small Craft Advisory conditions & possible gales are anticipated
Monday afternoon into Tuesday, with headlines becoming necessary as
this portion of the period draws closer. Shower and storm chances
will accompany the gusty winds.

Quigley

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory...LMZ643 until 7 PM Friday.

&&

$$

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