NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 112358 AAA
AFDMKX

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

.KEY MESSAGES...

- Moderate Swim Risk until early to middle evening at Sheboygan
  County beaches. Small Craft Advisory expires early this
  evening north of Port Washington.

- A few light sprinkles or showers possible early Saturday
  morning across the west.

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

&&

.UPDATE...
Issued 658 PM CDT Fri Sep 11 2026

South southeast winds at the lakeshore in Sheboygan County will
continue to slowly weaken into the early to middle evening hours.
Waves of 3 to 4 feet early this evening will subside to around
2 feet by middle evening. Thus, the Moderate Swim Risk will
linger into the early to middle evening hours.

A cold front will move east toward the area tonight, shifting
east through the area on Saturday. There is a lot of dry air in
the low levels (mainly below 8000 feet AGL) that may limit any
weak showers or sprinkles from reaching the ground. There should
be some middle to high clouds that move through. May see some
diurnal cumulus clouds develop later in the morning into
Saturday afternoon, as winds shift from the south to the west
northwest behind the front. Some gusts of 15 to 20 MPH may occur
on Saturday ahead of and behind the front.

Lows tonight should be in the lower to middle 60s, with highs
Saturday in the upper 70s northwest to lower to middle 80s
southeast.

Wood

&&

.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 658 PM CDT Fri Sep 11 2026

Southeast winds should linger into the middle evening hours for
terminals near Lake Michigan and Waukesha, as the lake breeze
continues to push inland. This may reach Janesville and Madison
before ending early this evening. Winds should become south
later this evening and southwest later tonight into early
Saturday morning, with some gusts to 15 knots by middle morning
Saturday.

A cold front will move east toward the area tonight, shifting
east through the area on Saturday. There is a lot of dry air in
the low levels (mainly below 8000 feet AGL) that may limit any
weak showers or sprinkles from reaching the ground. There should
be scattered to broken middle to high clouds that move through.
May see some diurnal cumulus clouds around 3500 feet AGL develop
later in the morning into Saturday afternoon, as winds shift
from the south to the west northwest behind the front. Some
gusts of 15 to 20 knots may occur on Saturday ahead of and
behind the front.

Wood

&&

.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.

&&

$$

Visit us at weather.gov/milwaukee

Follow us on Facebook, X, and YouTube at:
www.facebook.com/NWSMilwaukee
www.x.com/NWSMilwaukee
www.youtube.com/NWSMilwaukee