833
FXUS63 KMKX 220321
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1021 PM CDT Mon Jul 21 2025

.KEY MESSAGES...

- High swim risks due to building waves and dangerous currents
  for Ozaukee and Sheboygan county beaches Tuesday morning into
  early tuesday evening. Moderate swim risk for Milwaukee and
  Racine county beaches as well.

- Scattered showers and storms will be possible at times Tuesday
  evening/night into early Wednesday morning, but uncertainty
  remains high.

- Dangerous heat building into the state Wednesday and
  Thursday. Heat indices of 100 to 107 degrees are expected. An
  Extreme Heat Watch is in effect starting Wednesday.

- Increased shower and thunderstorm chances (>50%) for Thursday
  with periodic chances through the end of the week into the
  weekend.

&&

.UPDATE...
Issued 1015 PM CDT Mon Jul 21 2025

The forecast for overnight and Tuesday remains on track. Wave
heights still expected to climb to around 3 to 5 ft for
Sheboygan and Ozaukee county beaches on Tuesday due to a steady
15-20 KT southeasterly wind fetch over Lake Michigan, leading to
a High Swim Risk. Moderate swim risk then expected further
south. Dry weather still looking likely overnight and through
the daytime hours of Tuesday.

One (potentially significant) pivot that we are beginning to see
in short term model guidance is the development of convection
over central and northeastern Iowa mid to late Tuesday
afternoon, which then manages to sustain itself overnight as an
MCC or MCV and track eastward across our CWA after midnight
Tuesday night through around 10 AM Wednesday morning. Though
this solution is not perfectly agreed upon amongst model
guidance, a consensus between the 00z HRRR and 00z NamNEST (two
models which are usually greatly opposed) is of great interest.
If this scenario were to play out, thunderstorm chances could
increase substantially for the Tuesday night period, and heat
index values on Wednesday could drop a bit (due to lingering
cloud cover). The ongoing forecast iteration will focus on the
validity of this scenario, presented in these most recent CAMs.

Sheppard

&&

.SHORT TERM...
Issued 321 PM CDT Mon Jul 21 2025

Tonight through Tuesday night:

High pressure centered over the Upper Great Lakes region
continues to bring prevailing easterly flow across southern WI
this afternoon and evening. This is helping keep a drier and
more stable environment across the area. However the CAPE
gradient is creeping a bit further northward into the evening as
the high pressure slides eastward. Thus the ongoing convective
activity associated with the remnant MCV upstream in southeast
MN may continue to follow this instability gradient
southeastward through the evening. While latest tracking of the
ongoing convection suggests it should stay southwest of the CWA
given the dry airmass in place, still can not rule out the
upstream activity expanding a bit more eastward as it progresses
and clip areas west to southwest of Madison with some showers
or maybe even a rumble of thunder or two through the evening as
the mid-level shortwave trough works its way through the
region.

Otherwise an upper-level ridge establishes itself over the
Upper Midwest overnight into Tuesday. Will see southerly winds
advect in warmer temps. Looking at high temps climbing into mid
to upper 80s in the afternoon with heat indices in low to mid
90s for inland areas of southern WI. May see more of a south-
southeasterly flow off the Lake so areas along the lake may stay
a bit cooler in the upper 70s to lower 80s. Persisting
southerly flow will also contribute to building waves along
southern WI beaches with waves up to around 4 ft for Ozaukee and
Sheboygan County beaches late Tuesday morning into Tuesday
evening. Overnight will be mild as well with low only dipping
into the 70s.

Continue to see a variety of solutions for Tuesday evening into
Wednesday morning regarding another mid-level shortwave trough
traversing the region and bringing a round of showers and
storms. Given the variability, difficult to pinpoint, but at
this time, it does look like the shortwave trough undercuts the
upper-level ridge through Tuesday afternoon and into the
overnight. This will line up with increasing moist tongue where
PWATs gradually climb to above 1.5 inch into Wednesday morning.
However, it does look like there is better forcing further
north into northern WI given a strong LLJ and low-level WAA
ahead of a surface front. Thus will maintain limited (<30%) PoP
chances, but will be a potential to see some scattered activity
later Tuesday evening/overnight.

Wagner

&&

.LONG TERM...
Issued 321 PM CDT Mon Jul 21 2025

Wednesday through Monday:

Ridging will continue to sit over the eastern CONUS mid week
and into the weekend. A shortwave trough will move through and
deepen in the lee of the Rockies creating sfc low pressure. This
area of sfc low pressure will move northeastward into Nebraska
then southern Minnesota and eventually northern Wisconsin by
Thursday. Strong WAA will move in across southern Wisconsin as
winds turn southwesterly. The breezy southwest winds should be
more than enough to overcome any lake breeze activity which will
push the hot temperatures right up to the Lake shore. There
remains a small chance (10-15%) for a isolated shower or storm
Wednesday with the best chances across central Wisconsin
counties. Guidance has a MCS rolling through northern and
central Wisconsin heading southeastward overtime. Confidence is
low on if this will hold together long enough to clip these our
northern CWA, but its never the less non-zero. The long and
short of it is this MCS type system on CAMs and other guidance
will be moving into a less dynamically favorable environment.
Jet dynamics aloft will be better to the north due to the
ridging and LLJ will be veering out of southern Wisconsin. Good
heat, good moisture, but no lift. Outside of central Wisconsin
the rest of the area should stay predominately sunny with highs
in the low to mid 90s. Heat indices will quickly climb
throughout the day with values of 100 to 107 expected. An
Extreme Heat Watch was issued for Wednesday through Wednesday
night due to the high heat and the lack of overnight recovery
opportunities. Overnight lows are expected to be in the low to
mid 70s with another hot day expected Thursday.

Later in the day Thursday into Thursday night there will be
some relief. Mainly in the form of increasing clouds early on to
increasing chances for rain. This all starts with the
aforementioned sfc low pressure, frontal boundary and the
shortwave moving in. The shortwave and frontal boundary will sag
southward overtime resulting in some 60% POPs for Thursday
evening. Exact timing and location for rain/storms is still a
bit uncertain and this is largely due to the fact that this
again looks like a MCS type structure. Its path and timing will
largely depend on what happens into the hours leading up to it
and even the day prior. Which is in part why the chances are
lower around (50-60% the last couple runs). This then plays a
role in the heat, if clouds stay clear of the area or are slow
to move in temperatures will climb. This too means rainfall will
slow which means people in southern Wisconsin will have to wait
longer for the evaporational cooling and relief. So at its
worst, Thursday could be another day of heat indices around 100
to 105 degrees. That being said, if things move in earlier then
conditions will be cooler.

Low chances for rain and thunderstorms continue into Sunday as
additional shortwave troughs move through the flow. The near
stationary sfc front/sfc trough will remain to the south and
within close proximity to Wisconsin. There should be some relief
from the heat into the weekend but not much. High temperatures
are expected to remain in the mid to upper 80s.

Patterson

&&

.AVIATION...
Issued 1020 PM CDT Mon Jul 21 2025

Dry weather looking most likely from now through Tuesday
evening. VFR and scattered high clouds expected for the majority
of the overnight, with 1,800 to 3,000 ft MVFR cloud ceilings
currently observed over eastern IA / southern MN expected to
drift eastward into south central and southwestern WI late
overnight into Tuesday morning, likely lifting / scattering a
bit before progressing any further eastward. Said clouds will
devolve into diurnal cumulus throughout Tuesday, at scattered to
occasionally broken coverage around 5,000 ft (hence VFR is
likely for most areas Tuesday afternoon). South to southeast
winds build at daybreak Tuesday, with occasional 15-17 KT gusts.

A south breeze is expected to continue overnight Tuesday night,
with some potential for thunderstorms after midnight Tuesday
night through Wednesday morning. Exact chances / timing remains
uncertain.

Sheppard

&&

.MARINE...
Issued 321 PM CDT Mon Jul 21 2025

High pressure across the Upper Great Lakes looks to slide
eastward overnight with building southerly flow. this will
result in waves up to around 4 feet impact central and northern
WI beaches on Tuesday, thus a small craft advisory has been
issued late Tuesday morning through early Tuesday evening. Low
pressure deepens across the Upper Midwest Tuesday bringing
periodic shower/storm chances across the Lake Tuesday
evening/night. Then as the low pressure gradually slides
eastward, expect it and its associated cold front to push
through by the end of the week bringing additional shower/storm
chances along with a west to northerly wind shift.

Wagner

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Beach Hazards Statement...WIZ052-WIZ060...9 AM Tuesday to 7 PM
     Tuesday.

LM...Small Craft Advisory...LMZ643-LMZ644...9 AM Tuesday to 7 PM
     Tuesday.

&&

$$

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