441
FXUS63 KMKX 122004
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
304 PM CDT Fri Sep 12 2025

.KEY MESSAGES...

- Dense fog is lingering over the nearshore and open lake areas
  north of Milwaukee and will gradually dissipate from the
  south through the evening.

- Chances (30 to 50 percent) for showers and thunderstorms
  tonight through Saturday morning. Heavy rain, small hail and
  gusty winds are possible.

- High temperatures climbing above normal through the weekend,
  with humidity increasing as well.

&&

.SHORT TERM...
Issued 304 PM CDT Fri Sep 12 2025

Tonight through Saturday night:

We may see dense fog develop toward Sheboygan once again late
this evening as this area will still be under a moist marine
influence. Fog will be less of a concern elsewhere tonight.

There are several clusters of thunderstorms ongoing over many
areas of Minnesota this afternoon, and also a weaker area of
convection over northern Iowa. They are within an area of low
level warm air advection, the nose of the low level jet, a
shortwave trough (and possible MCV), and the entrance region of
an upper jet. The clusters of storms should generally track
eastward across central and southeast MN (and eastern IA) this
afternoon, right along the CAPE gradient.

For this evening, the convection should weaken as it gets into
western WI and especially south central WI because it will be
drifting out of the favorable instability and shear region.
However, the GFS weakens the LLJ but still gradually leans it
over into south central WI just prior to midnight and then
strenghthens and veers the LLJ through southern WI Saturday
morning. It therefore brings the area of showers and
thunderstorms through southern WI slowly overnight through
Saturday morning. This scenario genearlly makes sense and our
forecast precip (PoPs) follow this idea.

The meso models have a general sense of this scenario, with
mixed degrees of weakening and strengthening through the period.
Most models agree that the convection will exit southeast WI by
1 PM Saturday. Warm air advection will be the dominant forcing,
and there should be elevated CAPE of up to 500 j/kg late
tonight into Saturday morning, so a few thunderstorms with hail
and some gusty winds are possible. Surface- based CAPE will
increase with the daytime heating over south central WI, but
will likely be impeded by the cooler marine- influenced air over
southeast and east central WI. However, the wind shear is
expected to be highest over east central WI during the mid
morning due to the LLJ and a passing shortwave origininating
from nrn MN. SPC has all of southern WI in a marginal risk for
severe storms and this seems warranted.

Additionally, the precipitable water values will be in the 1.5
to 1.75 inch range, so very efficient rainfall is expected.
Showers will be slow-moving, so any stronger cells will have the
potential to drop an inch of rain within a half hour. While
flooding is not an immediate concern, if storms can regenerate
over the same area due to the LLJ sitting over south central WI,
then heavy rain and flooding could become a threat.


Warm and more humid air will push into southern WI behind the
precip Saturday afternoon on steady southerly winds.
Temperatures will depend on how quickly our clouds clear, so our
highs are in the lower to mid 80s over southwest WI, and in the
mid 70s near the lakeshore. Lows Sat nt should be around 60.

Cronce

&&

.LONG TERM...
Issued 304 PM CDT Fri Sep 12 2025

Sunday through Friday:

The warm and humid ridge will push into southern WI by Sunday,
although a southeast wind component will keep east central and
lakeshore areas of southeast WI cooler once again. Inland areas
should reach mid 80s central (including Madison) and upper 80s
west.

The upper level ridge will be stuck over the Great Lakes, with
an upper trough over the Northern Plains, through at least the
middle of next week. Southern WI will remain in southerly flow
but with a southeast lake breeze each day. Monday and Tuesday
will be the warmest for inland areas, with highs in the mid to
upper 80s. Lakeshore areas will be in the upper 70s with a
chance for lower 80s depending on the timing of that lake
breeze.

Rounds of showers and thunderstorms associated with the
upper trough will remain over the northern Plains during this
time. We may see clouds from this system west of Madison at
times, but no precip is anticipated. The trough is expected to
finally slide across the Upper Great Lakes Thursday night
through Friday, although the GFS tries to bring this through a
little earlier.

Cronce

&&

.AVIATION...
Issued 304 PM CDT Fri Sep 12 2025

Dense fog and low ceilings are possible once again from late
evening through the overnight toward Sheboygan and potentially
along other lakeshore areas. Expecting it to remain north of
Milwaukee, but we will keep an eye on it.

Showers and thunderstorms that are currently over south central
MN and north central IA will trek eastward to reach south
central WI late this evening, but a weakening/diminishing trend
is expected. However, showers and thunderstorms will be possible
at times across all of southern WI during the overnight hours,
with chances increasing Saturday morning. Any strong storm will
have the potential for heavy rain, hail, and brief gusty winds.

Cronce

&&

.MARINE...
Issued 304 PM CDT Fri Sep 12 2025

The majority of the fog between Sheboygan, Port Washington, and
mid lake as dissipated, per the latest satellite imagery. Dense
fog with visibility below 1 NM is expected to expand and persist
over much of the north half of Lake Michigan tonight through mid
Saturday morning.

Low pressure around 29.6 inches over the northern Great Plains
will remain in place through early next week. Lake Michigan will
have south to southeast flow tonight into Saturday. An area of
showers will cross WI and Lake Michigan tonight through Saturday
afternoon. Winds will gradually become northeast Saturday night
into Sunday, as a frontal boundary shifts south and high pressure
around 30.3 inches develops in Quebec. Winds will increase out of
the south early next week.

Cronce

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Dense Fog Advisory...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ868 until 10 AM Saturday.

     Dense Fog Advisory...LMZ643-LMZ644-LMZ669-LMZ671-LMZ870-LMZ872
     until 10 PM Friday.

&&

$$

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