502
FXUS63 KMKX 172031
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
331 PM CDT Sun Aug 17 2025

.KEY MESSAGES...

- Beach Hazards Statement in effect for waves of 3-6 feet through
  at least Monday morning

- Multiple rounds of showers and thunderstorms are likely late
  tonight through Monday night. Locally heavy rainfall is
  possible.

- The rain over the next couple of days could lead to river
  rises again, with the potential for a few locations to return
  to at least minor flood stage.

- Drying out and becoming less humid by Wednesday.

&&

.SHORT TERM...
Issued 330 PM CDT Sun Aug 17 2025

Tonight through Monday Night:

Today was a reset day for the atmosphere in southern WI. We had
a temporary drying with gusty northeast winds off Lake Michigan
that spread inland, dropping dewpoints into the lower-mid 60s.
Temperatures topped out in the 70s for most sites except around
80 toward Platteville, thanks to the extensive cloud cover.

We are waiting for the low level jet to ramp up this evening,
and it will likely be pointing into southwest MN where a surface
low will be located. The 850mb temp and also the CAPE gradient
will stretch southeast through northeast IA and southwest WI in
the early evening and remain fairly stationary overnight. The
low level jet is expected to expand eastward into southeast MN
and possible southwest and west central WI late tonight into
Monday morning. If a portion of that LLJ makes it over southern
WI, then scattered, elevated showers and thunderstorms will be
possible. I held off until after midnight to add chance pops to
the forecast to account for this.

The main thing that should happen tonight is for a thunderstorm
complex to develop over south central MN. Where the complex goes
is less certain. It may ride ESE along the CAPE/850mb temp
gradient overnight, which would put the complex somewhere near
northern IL or south central WI by mid Monday morning. The
other possibility is that the complex would lift into northern
WI with the push of the LLJ and stronger warm air advection. A
compromise between the two solutions would slide it into
southern WI or weaken it by the time it gets here. The bottom
line is that the probability of getting storms in southern WI
is still less than 50 percent.

For the afternoon, a mid level shortwave trough will be crossing
WI. This will help amplify some low level warm air advection
into southern WI. Lift will be aided by upper divergence with
the right entrance region of an upper jet as well. Therefore,
there is slightly higher confidence (60 to 75 percent chance) of
thunderstorms in eastern and portions of south central WI
during Monday afternoon and early evening. This will also be the
time period of peak instability (over 1000 j/kg CAPE) and modest
bulk shear (approx 25 kt). With the moist adiabatic profile,
wet microbursts would be the concern again.

As for the flash flooding potential, southern WI remains in a
slight risk for excessive rain by WPC and this is appropriate.
However, if we do not see the morning convection, then the risk
of flash flooding will be lower since the afternoon convection
looks more progressive.

A Beach Hazards Statement for a High Swim Risk remains in effect
until 1 PM Monday but this may need to be extended through 7 PM.
The gusty northeast winds today will shift to the southeast
Monday morning. High waves will be slow to diminish Monday
afternoon.

Cronce

&&

.LONG TERM...
Issued 330 PM CDT Sun Aug 17 2025

Tuesday through Sunday:

A few storms may linger in the east Tuesday, but most guidance
points to everything exiting by then.

High pressure will settle over the Upper Great Lakes area by
Tuesday evening, which will end our chance for storms. One
caution to that idea is that a weak trough may stall over the
eastern Great Lakes and clip Lake Michigan (and far southeast
WI) with surprise showers and/or storms on Wednesday. Thursday
and Friday look quiet for southern WI.

A robust upper low may set up over Quebec and usher cooler air
in the Upper Great Lakes. A few sprinkles with stratocu may
occur Saturday afternoon and Sunday afternoon.

Cronce

&&

.AVIATION...
Issued 330 PM CDT Sun Aug 17 2025

MVFR ceilings are hanging on over much of southern WI, with some
clearing along Lake Michigan due to the drier air. With the northeast
winds reinforcing a low level inversion and no change
anticipated, the low clouds may hang on through much of the
night.

Thunderstorms are possible over south central WI Monday morning,
but more likely over southeast WI during the afternoon. Expect
gusty southeast winds to develop along Lake Michigan Monday
morning and increasing southerly winds elsewhere through the
afternoon.

Cronce

&&

.MARINE...
Issued 330 PM CDT Sun Aug 17 2025

Low pressure will continue toward the Atlantic tonight with
high pressure developing across Ontario. The low will continue
to have an associated front draped across parts of the Great
Lakes region which will remain the focus for thunderstorm
development through Tuesday morning. Developing low pressure
over South Dakota will move into southern Minnesota overnight.
This will be the renewed focus for storm development late
tonight throughout Monday.

Winds will shift north to northeast today and southeast Monday
morning. A period of south are possible Monday morning. Once the
next system pushes out we will see a return to more northerly
flow across the lake from Tuesday through Friday.

The onshore winds will create high waves and a Small Craft
Advisory is in effect.

Cronce

&&

.HYDROLOGY...
Issued 330 PM CDT Sun Aug 17 2025

Ponding of water in areas immediately near each river segment
will remain possible with any additional rainfall.

There is potential for localized heavy rainfall again tonight
through Monday, and area rivers (particularly in the Milwaukee
metro area and surrounding counties) will be monitored for
potential rises.

Cronce

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Beach Hazards Statement...WIZ052-WIZ060-WIZ066-WIZ071-WIZ072
     until 1 PM Monday.

LM...Small Craft Advisory...LMZ643-LMZ644-LMZ645-LMZ646 until 1 PM
     Monday.

&&

$$

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