123
FXUS63 KMKX 180306 AAB
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
1006 PM CDT Sun Aug 17 2025

.KEY MESSAGES...

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

- Multiple rounds of showers and thunderstorms through early
  Tuesday morning. Lightning and heavy rainfall are the main
  concerns tonight into Monday morning. Localized damaging winds
  are an additional concern Monday afternoon through Monday
  night.

- River rises will greatly depend on where the heaviest rain
  occurs tonight through Tuesday morning, with rises to minor
  flood stage if rain falls in our most saturated regions.

- Drying out and becoming less humid by Wednesday.

&&

.UPDATE...
Issued 1005 PM CDT Sun Aug 17 2025

Incoming 00z guidance offering only minor changes to the going
forecast, much of the updates are based on radar trends and
expectations with various low level boundaries tonight.

While trust in any specific model has been a fools errand
lately, there are a few important details to glean that should
dictate how rain/storm chances evolve from the rest of tonight
through early Tuesday morning. The biggest overarching theme is
that the key players will be thunderstorm complex (MCS)
development (over MN/SD/IA), their resultant movement, and any
MCVs that result from these MCSs. Knowing the recent track
record of the mesoscale models, hanging ones hat on individual
run is not recommended. That said, the incoming guidance each
has general ideas of how things may evolve.

For the rest of tonight, our shower/storm development will be
tied to low level wind shifts, notably in the 925 to 850mb
layer. Scattered development in this warm advection/isentropic
upglide regime is plausible given the moist airmass in place.
Development will be decidedly elevated, with no real movement in
the lower level airmass as east to southeast winds remain in
place overnight. Lightning and locally heavy rainfall will
accompany storms, but they will be transient...in and out.

Heading into the daylight hours of Monday morning, the first
scenario to watch for is any MCS that gets a head of steam
eastward out of SD. While there will be some elevated
instability to maintain showers/storms, if this scenario plays
it would move over southern WI prior to noon. Another potential
scenario is for the MCS to ride the instability axis to our
southwest and clip southwestern WI. Both scenarios prevent much
in the way of airmass recovery until the afternoon hours.

The next scenario to watch for is MCV development. This will be
a mesoscale forecast problem as placement/movement will be
dictated by overnight convection. Assuming some degree of
airmass recovery, during the afternoon, an MCV passage would
locally alter/increase our severe risk (mainly locally damaging
wind, but a non-zero chance for a tornado). Finally there is the
synoptic boundary itself. If the MCV is located elsewhere, the
front will be the last opportunity for shower/storm development
during the evening and into the early overnight hours Monday
night.

Bottom line there are multiple features we will have to track in
the mesoscale forecast Monday and Monday evening, with multiple
ways to see storm development. The good news is that the trend
to have the front exit the area Tuesday continues and
quieter/drier weather settles into the region for the mid/late
week.

Gagan

&&

.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 1005 PM CDT Sun Aug 17 2025

The primary forecast challenge continues to be timing multiple
rounds of showers and storms. Will continue to use PROB30 groups
to highlight general timeframes where convection is possible,
with amendments to hone in on development and timing. Overall,
ceiling/visibility will be VFR, with occasional bouts of MVFR
stratus overnight. Any storms will be capable of producing
shorter periods of IFR visibility. Scattered storms are expected
through Monday morning, with redevelopment from west to east
during the afternoon and evening, ending overnight Monday night.

Will need to keep an eye on how fast we clear out Monday night
as this may lead to patchy fog. Right now that risk appears to
be west and north of Madison, but bears watching.

Gagan

&&

.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