NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 231212
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
712 AM CDT Thu Apr 23 2026

.KEY MESSAGES...

- Periods of showers and storms (60-90 percent chance) expected
  late this evening through tonight. There is a Marginal Risk
  for severe storms mainly for damaging winds. Can't rule out
  isolated large hail or a brief spin up across southwestern
  Wisconsin.

- Dry weather with highs in the 60s this weekend; cooler by Lake
  Michigan due to light easterly winds.

- Showers and thunderstorms return late Sunday night through
  Monday night.

&&

.UPDATE...
Issued 710 AM CDT Thu Apr 23 2026

No major changes to the going forecast. The latest guidance from
CAMs indicates the ~7-11 PM window of scattered thunderstorm
activity towards southwestern WI remains on track, followed by
additional thunderstorms congealing into a line and sweeping
eastward across the entire region through tonight. The best
potential for severe weather remains from Madison westward.
Central and southwestern WI have the highest potential /
expected amounts for rainfall tonight due to the potential for 2
rounds of convection: the scattered activity this evening and
the line of thunderstorms later tonight. Areas further east may
only observe the fast-moving line of storms late tonight,
resulting in lower rain totals.

Sheppard

&&

.SHORT TERM...
Issued 1202 AM CDT Wed Apr 22 2026

Tonight through Friday:

An upper level trough is out over the Northern Plains and south
central Canada tonight. As this upper level cyclogenesis stays
near stationary, a shortwave trough will advect northeast out of
the Central Plains toward Wisconsin this evening. until the
shortwave begins to move toward the state party cloudy to mostly
clear skies with above normal temperatures are expected today.
Breezy south winds will develop this afternoon as temperatures
start to climb.

As the shortwave moves through, a cold front will move
southeast down the state. There is a 60-90% chance for a
scattered to isolated line of rain and storms to move through
late this evening into Friday morning. This line of storms ahead
of the cold front will initially be more persistent/continuous.
As this line moves east overtime it will be moving into a
slightly less favorable environment which will result in the
scattered nature. This weakening trend is represented well in
all the CAMS. This is in part due to the weak effective shear
which will struggle to remain around 20-30 knots by early Friday
morning. Western and southwestern Wisconsin will be in a far
better environment for strong to severe storms with damaging
winds being the primary threat. Can't rule out the briefing tor
or hail until the storms become more scattered and isolated. The
main hazard/concern will quickly transition to only damaging
winds by early Friday morning for eastern Wisconsin.

In addition to the severe thunderstorm potential this evening
into Friday morning. There will be a concern for flooding. Given
the antecedent conditions we already have of a very wet
environment, any rainfall that gets near an inch will
potentially cause problems. Many low lying areas and rivers
already out of their banks may see little impacts. However urban
and small stream concerns will be the primary threat with their
quicker responses to more incoming water. This system should be
fairly progressive, but can rule out an inch with locally higher
amounts toward two inches for southwestern Wisconsin. The last
thing worth mentioning with this system, is the severe potential
will increase if storms move through earlier than anticipated.
The later start time with the loss of some of the diurnal
instability and better shear is the main reason for the
scattered nature of the line. So the later the better if you are
looking to avoid strong storms.

Patterson

&&

.LONG TERM...
Issued 1202 AM CDT Wed Apr 22 2026

Friday night through Tuesday:

The upper level low across the northern plains and south central
Canada will continue to spin over that region through the weekend.
Behind the cold front from Friday, a sfc high pressure system
will move through Wisconsin Saturday and exit to the east Sunday
morning. With the upper level cyclogenesis out to our west and sfc
high pressure conditions will remain dry with light winds through
the weekend. Until the sfc high moves east of the state winds will
remain predominately northerly. Winds will then shift to
easterly then southeasterly Sunday as the high exits and the
upper level trough advances east toward the Great Lakes Region.

This trough (in northern Plains) and a shortwave out of the Rocky
Mountain west will advance toward the Great Lakes Region bringing
the next chance for rain and storms Monday. Confidence in rain
chances are high around 60-80%, but some uncertainty still remains
in exact timing of the rain. This is largely in part due to how
fast the shortwave and upper level trough advance east into
Wisconsin. You can see the time discrepancies easily in the
deterministic, but it also shows up in the ensembles and cluster
analysis. For the cluster analysis you can see that the upper
level trough out of the Plains has a persistent dipole pattern.
Supports and highlight the uncertainty in the position and
timing of the trough.

Not anticipating anything more than a few rumbles of thunder
for Monday. The features to keep an eye on will be the track of
the Low and if the warm front can make it far enough north to
make conditions unstable. Guidance generally tries to keep the
state north of the warm front which keeps the better conditions
for strong storms to our south. PWATS will also increase out
ahead of this system with values around 1 to 1.25 possible. With
how saturated the ground is already this spring it wont take a
whole lot of extra rain to potentially cause some concerns. The
current expectations are for widespread values around an inch.
So given the uncertainty in the timing and position of the
trough this will be a time to keep an eye on the weather.

Beyond Monday, low chances for rain look to linger (10-20%).
Don'tanticipate this to be another multi day rain event like
the week prior, but that slow moving upper level trough that
brought us rain on Monday will be slowly spinning across the
Great Lakes through mid week. Any additional shortwave troughs
or presence of an upper level jet could create just enough lift
to get sporadic light rain. Given that guidance is all over the
place on whether or not to be dry which is why chances are low.

Patterson

&&

.AVIATION...
Issued 710 AM CDT Thu Apr 23 2026

Dry weather and VFR this morning and afternoon, with
accelerating south winds. A southeasterly lake breeze is
expected to progress ~10-15 miles inland through this afternoon,
and the remnants of it may sweep further westward into this
evening.

From roughly 7-11 PM CDT, scattered thunderstorms
expected to stray into southwestern WI, some could become strong
with gusty winds and isolated large hail. Additional showers
and thunderstorms then congeal into a line and progress eastward
across the entire region through tonight (timing reflected in
TAFs). Best potential for strong / severe storms is in the
evening (Madison and points westward), with a weakening trend
expected as storms track east. Cloud ceilings might decline to
MVFR / Fuel-Alt MVFR levels in the event of continued
rainshowers late tonight, but should gradually lift post-dawn
Friday morning if applicable.

Sheppard

&&

.MARINE...
Issued 1202 AM CDT Wed Apr 22 2026

Winds will veer southeast tonight and accelerate Thursday
afternoon becoming breezy through Friday morning as 29.2 inch low
pressure develops over the northern Great Plains. This low
pressure system will slowly track east toward the central portion
of the Lake Friday night. Some 30 kt easterly winds may occur over
the northern tip of the lake Thursday night and Friday.

A Small Craft Advisory may be needed for nearshore zones north of
Port Washington due to building waves. The persistent southeast
winds early Friday morning through Friday afternoon should cause
waves to build to around 4-6 feet.

The low will pull a cold front across Lake Michigan Friday
afternoon and evening, resulting in a breezy north-northwest wind
shift. Showers and thunderstorms are expected late Thursday night
through Friday, both ahead of and along the front. Severe weather
is not anticipated at this time.

Northerly winds will continue through the weekend across Lake
Michigan. 29.4 inch low pressure is forecast to track
northeastward from the central Great Plains (Sunday night) near or
over Lake Michigan (Monday night), with gusty east to southeast
winds ahead of its arrival and gusty west or northwest winds
behind it (into Tuesday). Not seeing widespread gale potential
with this system, though trends will be monitored.

Patterson

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory...LMZ643...4 PM Thursday to 1 PM Friday.

&&

$$

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