NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 060001 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
701 PM CDT Wed Aug 5 2026

.KEY MESSAGES...

- Isolated showers linger into this evening

- Areas of fog are possible tonight

- Heat & humidity return Saturday-Tuesday, along with periods of
  showers and storms

&&

.UPDATE...
Issued 701 PM CDT Wed Aug 5 2026

There is minimal instability left this evening, with only
isolated showers expected over the next few hours ahead of an
approaching shortwave. Surface high pressure will build in
overnight, with some decrease in clouds likely. It still looks
like fog will be possible later tonight into early Thursday
where there is clearing, given lingering low level moisture and
light winds.

DDV

&&

.SHORT TERM...
Issued 309 PM CDT Wed Aug 5 2026

Tonight through Thursday night:

A front that is stalled over southern WI and northern IL will
continue favor a chance of showers with a few thunderstorms
through the evening. The primary area of concern for
thunderstorms is over southeast WI (southeast of a line from
Janesville to Milwaukee) late this afternoon and potentially
into the early evening. We cannot rule out a stray shower
elsewhere this evening, but thunder is not likely.

The forcing for showers is 850mb warm air advection and
frontogenesis, and it is currently over eastern Iowa. We can
also see an uptick in the convection in northeast IA due to a
shortwave approaching. We are expecting that area of showers
and storms to track through northern IL late this afternoon and
into the early evening, but probably clip far southern and
southeast WI. There is a clear dewpoint gradient in far
southeast WI this afternoon, with a pocket of dewpoints in the
70s and other areas in the mid 60s or lower. This area has
higher instability, with CAPE around 1500 j/kg per the latest
SPC mesoanalysis page. So as the cluster of showers with
isolated storms tracks into northern IL, there is also an
increasing chance for storms in southeast WI. Even though there
is instability, there is very low shear, so the severe threat is
low (maybe small hail and some gusty winds lower than severe
thresholds).

Once the precip clears from west to east this evening, the low
level moisture will linger, indicated by dewpoints in the mid to
upper 60s. This moisture and the light winds will be conducive
for areas of fog to develop, maybe with 1 to 2 mile visibility.
Since low clouds may also linger, this is not a night where we
are expecting widespread dense fog (visibility of half mile or
less), but we will be watching trends, especially in river
valleys and other low-lying areas.

Diurnal cumulus clouds should develop in any areas where the
low stratus and high clouds clear Thursday morning. High
temperatures will range from around 80 toward central WI to the
mid/upper 70s in far southeast WI due to the lingering clouds.
Winds will remain light, but we can expect a lake breeze once
again. Thursday night lows will be around 60 Thursday night.
Patchy fog will be possible once again due to the lingering low
level moisture (as the front sits over northern IL).

Cronce

&&

.LONG TERM...
Issued 309 PM CDT Wed Aug 5 2026

Friday through Wednesday:

Warm and humid air will spread back into southern WI on
southerly winds Friday as a low pressure trough approaches from
the Northern Plains. Showers and thunderstorms are possible
along this front as it tracks through southern WI Friday night.
The timing of this front and also an inconsistency with
low/upper level forcing and some mid level dry air keep our
chances for storms low, especially our severe chances.

A northerly breeze is expected Saturday in the wake of this
front, with a weak lake breeze likely. Quiet weather with highs
in the lower 80s and dewpoints in the lower 60s will make for a
nice day.

Saturday night will begin a period of unsettled weather as we
get into mid level zonal flow due to broad high pressure over
the southwest U.S. and low pressure near Hudson Bay. Weak
ripples in the flow (mid level shortwave troughs) will cause
periods of thunderstorms, or potentially thunderstorm
complexes, to develop and track through southern WI. The first
main chance of storms that models are signaling should develop
on the nose of the low level jet over Iowa that could track
across southern WI and northern IL late Saturday night into
Sunday morning. Depending on the strength of that complex,
strong winds could be possible, but it is not quite in the
forecast range for predictability due to the weaker nature of
the upper wave.

The next shortwave that has consistency between the models is
expected to develop in the Dakotas Sunday night and track
across WI by midday Monday. We will need to watch our severe
chances with this one given the time of day.

Storm chances for southern WI beyond Monday will depend on how
Monday plays out, but models are favoring the effective front to
be south of WI by Tuesday. If the front can nudge back
northward, then our storm chances will return at times for the
latter half of next week.

Cronce

&&

.AVIATION...
Issued 701 PM CDT Wed Aug 5 2026

There is minimal instability left this evening, with only
isolated showers expected over the next few hours ahead of an
approaching shortwave. Ceilings will mainly be MVFR this
evening, but some improvement is gradually possible from the
northwest given latest satellite trends.

Surface high pressure will build in overnight, with some
continued decrease in clouds likely. It still looks like fog
will be possible later tonight into early Thursday where there
is clearing, given lingering low level moisture and light winds.

Not out of the question for a shower or two Thursday afternoon,
but most places will likely be dry tomorrow. Some lower ceilings
may linger in the southeast through at least the morning hours,
with a return to VFR conditions likely most places by the
afternoon.

DDV

&&

.MARINE...
Issued 309 PM CDT Wed Aug 5 2026

A stalled front is sitting over southern Lake Michigan this
morning. Light and variable winds can be expected through Thursday
as the front shifts south and weakens and high pressure moves
into the region. Intermittent showers with a few thunderstorms
are possible.

Patchy marine fog is possible due to warm and moist air over the
region. The areal coverage of the fog is not able to discern due
to the high clouds over the lake. Surface observations near the
lake are showing fog with visibility greater than one mile this
afternoon, and a ship ob over the center of the lake indicated
haze. So not thinking marine dense fog advisory at this time but
will continue to monitor trends through the night.

A prolonged period of south-southwest winds will then become
established across Lake Michigan late Thursday night through
Sunday, with the exception of northwest winds Saturday morning
with a brief cold frontal passage.

Cronce

&&

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

$$

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