761
FXUS63 KMKX 161517
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1017 AM CDT Wed Jul 16 2025

.KEY MESSAGES...

- Increasing tornado risk for this afternoon along with damaging
  winds and heavy rainfall, mainly between 2-7pm.

- Very warm and humid conditions today with maximum heat indices
  in the lower 90s for the first half of the day.

- Heavy rainfall with 1-2 inches will be possible this
  afternoon/evening, especially for areas north of I-94 where
  localized pockets of >2 inches will be possible and result in
  minor flood concerns for low-lying and urban areas.

- Looking cooler and drier Thursday into Friday May see
  elevated swim risk conditions Thursday, especially for areas
  south of Port Washington to the WI/IL lakeshore border.

- Unsettled weather returns for the weekend with 30-50% shower
  and storm chances Saturday and Sunday night.

&&

.UPDATE...
Issued 1017 AM CDT Wed Jul 16 2025

Main focus is on the severe potential today and how things
evolve this afternoon.

Currently, the remnants of a mesoscale convective vortex (MCV)
is analyzed in north central Iowa with a rapidly decaying band
of rain showers getting into southwest Wisconsin. Surface dew
points are solidly into the low to mid 70s across the corn belt
in IA/IL upstream from southern WI, which should help to keep
these dew points up ahead of the system with the strong
southerly low level flow in place. The early morning runs of the
RAP/HRRR show some mixing occurring and suggest that dew points
will drop into the mid-upper 60s as we warm and start mixing,
but I think that may be a bit much and that the models may be
under- doing instability a bit. 16.14z RAP analysis from the SPC
meso page already shows we`re at 2500 J/kg+ of SBCAPE in
eastern WI. Expectations are that the remnant mid to high level
cloud cover will dissipate through the morning ahead of the
system while lower level cloud cover develops ahead of the MCV.
This should allow for decent heating across southern WI through
the morning and early afternoon while dew points stay elevated.

Going into the early afternoon, the focus for the severe storms
will be along and ahead of the MCV and the cold front extending
south from it. Scattered convection is expected to develop well
out ahead of this feature in the early afternoon, but the main
concern for severe storms will be right along that feature.
Timing of this feature coming through will be ideal for severe
development with the center of the MCV looking to be near Sauk
county around 2-3pm with the boundary running south from it. An
unstable air mass will be in place ahead of this feature with
16.13z RAP forecasts showing about 2000-3000 J/kg of SBCAPE
pushing into southern WI with the highest values right along the
WI/IL line. There does appear to be a west to east boundary
extending east from the MCV as well which aligns along a
925-850mb surge of moisture and stronger winds. 16.13z RAP
forecast soundings show much of the instability is in the lower
portion of the profile with fairly warm temperatures way aloft
around 400mb up. This will likely limit any ice development and
more likely promote more of a wet microburst type of
environment given the influx of low level moisture. 0-3km CAPE
looks enhanced along and right ahead of the MCV and appears the
highest across south central WI between 20-23z.

Wind shear-wise, low level winds will veer and increase in
speed, particularly in the lowest 3km of the profile. This leads
to some well balanced and curved low level portion of the
hodograph in the zone just ahead of the MCV. Any extra south-
southeasterly component to the surface winds will just enhance
that veering. Mid level winds are okay at 30-40kts and do appear
to slightly increase as the mid level trough approaches. The
0-6km & 0-3km shear vector is out of the west-southwest, which
goes perpendicular to the boundary. Thinking initial storm mode
will be discrete and possibly supercellular before going
linear. 0-3km shear looks to be at 30kts or lower, so QLCS
tornado development may be tough and the line may just go
outflow dominant quickly. Therefore, the main tornado risk
appears to be with any storms that can remain discrete.

Considered a Flood Watch for Sauk County through Green Lake
County given the high moisture content and rainfall amounts, but
the storms look to be fairly progressive and not lingering, so
will be holding off on issuing a Flood Watch for those counties.

Halbach

&&

.SHORT TERM...
Issued 339 AM CDT Wed Jul 16 2025

Today and Tonight:

Will warm up fairly quickly through the morning with 80s by
mid- morning and muggy dewpoints creeping into the 70s. These
conditions will set the stage for our thunderstorm and heavy
rainfall potential this afternoon as a mid-level shortwave
trough and supporting upper- level dynamics work their way
across southern WI. The latest 00z suite of models continue to
favor a broken line of thunderstorms along with moderate to
heavy rainfall to develop over southwestern WI early this
afternoon and progress east-norteastward as an MCV is progged to
lift through the early evening. By sunset the bulk of upper-
level forcing shifts east as a surface cold front pushes through
southern WI. Looking at northerly winds with a cooler and drier
airmass to settle in overnight into Thursday behind the cold
front.

Severe Thunderstorm Potential:

While models have waffled over the past few days, we can now
see the whites of the MCV eyes which will be one of the main
focuses for this afternoon stronger to severe thunderstorm
potential. Currently the MCV sits over the NE/SD/IA border with
a decaying area of convection along it. Expecting the downward
trend in the convection to continue as much of the CAM guidance
along with short-range models prog this feature to lift across
IA through the morning then pushing into southwestern WI early
this afternoon. System is progressive and looks to push out over
Lake Michigan later this evening. Accompanying the MCV will be
a surface cold front behind it. So ample surface level forcing
to pair with the mid-level shortwave trough along with a narrow
band of 700mb frontogenesis, 850mb WAA, and nose of a 25-30kt
LLJ to support the convective development this afternoon.

While there is always a degree of uncertainty when it comes to
MCV, there has been a consistent signal between the models for a
north to south orientated line of thunderstorms to develop as
the MCV moves across southern WI. Main timing window for this
activity is between 17z-00z.

With ample surface and upper-level forcing aligns in the warm
sector of this system, the question shift to severe potential.
Overall, instability builds ahead of the MCV with HREF min
SBCAPE exceeding 1000 J/kg and mean SBCAPE values approaching
2000 J/kg. However the higher instability values favor southern
half of the CWA. Meanwhile the deep layer shear (0-6km) is
fairly meager (20-30kt) with the higher values (35 kt) favoring
the northern half of the CWA. So while the severe potential
exist across all of southern WI, there is a bit of an offset
between these higher values of these two parameters. Where the
higher values overlap will favor the better severe potential,
which based on the 00-06z CAMs is along and on either side of
the I-94 corridor.

Main concern with any stronger to severe thunderstorms embedded
within the line will be the damaging wind threat as DCAPE
values are progged to exceed 1000 J/kg and steep low-level lapse
rates (>7C/km). As stated above overall shear looks minimal and
same can be said for the 0-1km shear with most models progging
values less than 20 kt. While the overall tornado potential
remains low, cannot complete rule out the potential for a brief
spin up or two given the MCV forcing producing a locally
enhanced pocket of 0-1km shear near it. Severe potential will
quickly wind down after 00z as the MCV moves out over the lake
and the cold front pushes through the area.

Heavy Rainfall Potential:

On the other side (northern portions) of MCV, there is a
potential to see heavy rainfall mainly across our central WI
counties (Marquette over to Sheboygan Co.). This is where the
higher PWATs exceeding 1.75 and even 2 inches align with the
warm frontal feature and the MCV. This is where a more west to
east orientated band of convection could develop and move over
the same area producing 1-2 inch rainfall with localized pockets
potential exceeding 3 inches. However, at this time overall
confidence to see widespread flash flooding and and flooding
remains on the lower side as the latest 00- 06z model trend this
west to east line to track a bit further north into the Fox
River Valley. Also the progressive nature of this activity
along with this area not seeing any significant rainfall
recently favors any Flash Flood concerns to be localized.
Nevertheless will be something to monitor through the morning to
see if trends shift things a bit further south and slows down.

Wagner

&&

.LONG TERM...
Issued 339 AM CDT Wed Jul 16 2025

Thursday through Tuesday:

A few showers are possible Thursday morning, although the
forecast is trending drier. The cold front will finally make it
into southern WI by midday and clear the WI/IL border by late
afternoon. High pressure, lower dewpoints and cooler
temperatures will be a welcome relief for Thursday night and
Friday.

A little bit of the heat and humidity will begin to return
Saturday, along with shower and thunderstorm chances. A weak
shortwave is expected to track along a stalled frontal boundary
that should be draped across northern IL Saturday morning. That
shortwave will be convectively-induced, so there is a lot of
uncertainty in its timing and track. Meanwhile, a synoptic
shortwave should be crossing northern WI. Between the two
ripples in the upper flow, there will be thunderstorm chances
for southern WI Saturday afternoon and evening, but there is
uncertainty about strength and coverage.

A similar setup Sunday may bring additional storms, but there
is more uncertainty in this occurring. One more upper trough is
expected to track across the Upper Midwest Monday-Tuesday. After
that, models diverge significantly, with some bringing an upper
ridge with heat and humidity to southern WI, and others
bringing unsettled weather with repeated shortwaves.

Cronce

&&

.AVIATION...
Issued 1017 AM CDT Wed Jul 16 2025

Main focus is on lower flight conditions that will come in with
the storms today. Ceilings and visibility should drop below MVFR
and possibly IFR as the storms roll through. Timing of the
storms appears to mainly be between 2-7pm today with a line
moving from west to east across southern Wisconsin. Winds will
increase out of the north tonight behind a cold front and
approaching high pressure.

Halbach

&&

.MARINE...
Issued 339 AM CDT Wed Jul 16 2025

Southerly winds will increase this morning ahead of an
approaching low pressure and accompanying front. Expect the low
pressure over IA to move across southern WI this afternoon and
cross the middle portion of Lake Michigan through the evening.
Accompanying this system will be increased thunderstorm chances
which may produce strong, gusty winds across Lake Michigan
through the late afternoon and evening. Will first see northerly
winds gradually build down across the northern half of the lake
through the afternoon as the front shifts southeast ahead the
low pressure, which will move across the Lake later this
evening/tonight. Expect breezy northerly winds to migrate into
the southern half of the lake overnight and persist into
Thursday as high pressure builds into the Upper Midwest.
Lighter, shifting winds are expected for Friday as the high
pressure moves over the Upper Great Lakes. Increasing southerly
flow then returns for the start of the weekend.

Wagner

&&

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

$$

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