NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 121154
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
654 AM CDT Sat Sep 12 2026

.KEY MESSAGES...

- A few showers are slowly progressing eastward this morning. An
  isolated bolt of lightning is possible but not likely.

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

- Gales are possible later Monday into Tuesday across the Lake
  Michigan open waters. A Small Craft Advisory may eventually be
  needed Monday into Tuesday for the nearshore waters.

&&

.UPDATE...
Issued 655 AM CDT Sat Sep 12 2026

A few showers have persisted across southwestern Wisconsin this
morning, with an isolated bolt of lightning remaining possible,
but unlikely. Shower will continue to weaken as they move
eastward, with only brief rainfall expected. Southwesterly winds
this morning will shift to northwesterly this afternoon into
this evening as a cold front moves through. Even with this cold
front, the late timeframe of the frontal passage will allow for
highs around 80 degrees in much of southern Wisconsin. NAM Nest
still indicates some potential for isolated storms to develop in
southeastern Wisconsin during the frontal passage, but
confidence remains low as capping remains in place and other
CAMs have not joined in this solution.

MH

&&

.SHORT TERM...
Issued 1248 AM CDT Sat Sep 12 2026

Today through Sunday:

A cold front will move east toward the area overnight, shifting
east through the area on Saturday. There is a line of showers
and some storms developing ahead of the front from northwest to
west central Wisconsin, pushing slowly eastward. This activity
may develop further to the southwest over the next few hours, as
most of the instability is along and just ahead of the front.

Forecast soundings are showing a lot of dry air lingering in
the low levels (mainly below 8000 feet AGL) over the forecast
area overnight into Saturday. This may limit any showers or
sprinkles from reaching the ground, and should also limit the
advance of any convection. For now, will leave scattered
sprinkles in far west and northwest parts of the area overnight
into early morning, as the frontogenesis with the front weakens
as it shifts east and there is little to no other support for
upward vertical motion.

There is mean layer CAPE over 1200 to 1800 J/kg that develops
later today, highest in far southeast Wisconsin, with daytime
heating. However, forecast soundings are generally capped and
have a fair amount of warm air in the 5000 to 9000 foot AGL
layer help keep the capping in place. Thus, will leave the
forecast dry for now for the rest of today.

There should be some middle to high clouds that move through,
with some diurnal cumulus clouds that develops later in the
morning into this afternoon. Winds shift from the south to the
west northwest behind the front as it moves through. Some gusts
of 15 to 20 MPH may occur ahead of and behind the front. Warm
highs in the upper 70s northwest to lower to middle 80s
southeast are expected today.

High pressure should move east southeast into the area later
tonight into Sunday, with northwest winds bringing cold air
advection and somewhat cooler temperatures and dew points into
the area. Lows should drop into the lower to middle 50s over
most of the area tonight, with highs Sunday in the middle 60s to
around 70 degrees. Some passing differential CVA may help bring
isolated to scattered showers to the area Sunday as well,
though forecast soundings are showing only a few hours worth of
good saturation for this to occur. For now, kept 20 to 30
percent chances for showers at times on Sunday.

Wood

&&

.LONG TERM...
Issued 1248 AM CDT Sat Sep 12 2026

Sunday night through Friday:

High pressure will move east of the region Sunday night into
Monday, with increasing southeast winds on the backside of the
high keeping dry air in the lower portions of the air column.
This may help shunt back any advancing showers and storms to
later Monday or more likely Monday evening. Thus, chances for
precipitation are now lower (below 30 percent) in the eastern
parts of the area, and may need to be lowered more in the west
(currently 40 to 70 percent) in later forecasts, if this dry
look in the model trends continues. Chilly lows in the 40s
Sunday night should rebound into the upper 60s to around 70
degrees on Monday.

Models and ensembles suggest that the main area of showers and
thunderstorms should move into western parts of the area Monday
evening and elsewhere later Monday night. The low level jet feed
of moisture and upward vertical motion, along the surface warm
front, should help bring rounds of showers and some storms to
the area into at least Tuesday morning. Forecast soundings are
showing moist adiabatic profiles with tall skinny mean layer
CAPE that is modest at best and high precipitable water values
approaching or over 2.00 inches. Given this setup, some training
of convection may be possible, and locally heavy rainfall may
occur.

The deep layer (30 to 40 knots) bulk shear values are fairly
robust, though the poor lapse rates and tall skinny CAPE may
favor more heavy rainfall than strong to severe storms. Could
still see stronger storms with some gusty winds occur in this
setup. Will continue to message the heavy rainfall and perhaps
some stronger storms later Monday into Monday night/Tuesday.

There is more uncertainty if another round of showers and
storms with some heavy rainfall would occur later Tuesday into
Wednesday. The deterministic models are trending further south
of the area with this next round of precipitation, as high
pressure to the north shunts this activity southward. Ensembles
still have a fairly wet period during this time, though they may
not have caught onto this trend yet. For now, will leave higher
chances (40 to 70 percent) for showers and storms for Tuesday
into Wednesday, but adjustments downward may be needed if this
drier trend continues.

The high may linger through a good portion of the rest of next
week, so this drier trend may linger as well. Ensembles suggest
temperatures may remain near or a little below seasonal normal
values.

Wood

&&

.AVIATION...
Issued 655 AM CDT Sat Sep 12 2026

VFR conditions expected throughout today and tonight, with
ceilings around 5000 ft as weak showers work eastward this
morning. Scattered cumulus around 5000 ft remain, with high
level clouds expected to move in this afternoon along the cold
front. Isolated storms are possible along the cold front in far
southeastern Wisconsin this afternoon, but confidence is very
low (~10%). Ahead of the front, expect southwesterly winds
gusting around 20 kt. Behind the front, expect northwesterly
winds with gusts up to 15 kt. Cumulus ends around sunset, with
skies becoming mostly clear overnight. Northwest winds diminish
to become light and variable. Winds remain northwesterly and
begin to increase again into Sunday morning.

MH

&&

.MARINE...
Issued 1248 AM CDT Sat Sep 12 2026

Southerly winds will continue to increase overnight, as a cold
front approaches the region from the west. Winds will shift out
of the west northwest today, as the cold front moves across the
lake. Expecting wind gusts to remain primarily in the 25 to 30
knot range over the open waters, though a few gusts approaching
gale force may occur in far northern portions of the lake.
Isolated showers and thunderstorms are possible ahead of the
approaching cold front, mainly over northern portions of the
lake. Winds will approach Small Craft Advisory levels this
afternoon north of Port Washington.

High pressure around 30.2 inches will build in from the
northern Great Plains Sunday night into Monday, bringing
decreasing winds Saturday night through Sunday, and winds
gradually shifting to the east and southeast and increasing
Sunday night into Monday. The high will move east of the waters
Monday afternoon and evening.

Winds will increase further and veer south southwest Monday
night into Tuesday, as low pressure around 29.4 inches develops
over Manitoba. Gales continue to appear likely during this time
frame, with headlines becoming necessary in later forecasts if
trends continue to hold. A Small Craft Advisory will eventually
be needed for the nearshore waters as well Monday into Tuesday,
for increasing winds and building waves. Some gales may occur
here as well during this period.

Periods of showers and thunderstorms will accompany the
developing low from as early as Monday evening into Tuesday.
Winds will trend northerly and weaken behind a cold front
Tuesday night into Wednesday.

Wood

&&

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

$$

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