NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 011051 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
551 AM CDT Tue Sep 1 2026

.KEY MESSAGES...

- Patchy fog is possible early this morning and could be dense
  in spots.

- Unseasonably warm and muggy conditions continue through the
  end of the work week. Upper 90s to near 100 degree heat
  indices will be possible daily in areas experiencing ample
  sunshine.

- Occasional storm chances continue into the beginning of the
  weekend, with plenty of dry periods in between. Some storms
  could be on the stronger side.

&&

.UPDATE...
Issued 550 AM CDT Tue Sep 1 2026

Patchy fog early this morning should remain about the same or
improve over the next couple hours as high clouds continue to
push in from the west. The fog will completely dissipate by
mid-morning after daytime heating kicks in.

Not out of the question for an isolated shower or storm this
morning given a little upstream activity. Otherwise, forecast
highs pushing or reaching 90 are still expected given the
persistent warm airmass. Heat indices in the mid to upper 90s
are likely with dewpoints into at least the low 70s.

DDV

&&

.SHORT TERM...
Issued 1210 AM CDT Mon Aug 31 2026

Current Overnight through Wednesday:

Synopsis/Mesoanalysis: Large areas of clearing prevail at the
current hour after a mainly storm-free evening across southern
Wisconsin. Main exception is near & just south of the Wisconsin-
Illinois border, where a ~20 knot low level jet is producing just
enough isentropic ascent for some cumulus clouds & very light
showers. This low level jet is expected to persist through the
remainder of the overnight hours, with a few sprinkles possible in
state line counties through daybreak. Elsewhere, areas of clearing
will combine with weakening surface winds to support areas of fog
development through daybreak. Some locally dense fog is possible.
Another warm & humid day is in store for Tuesday as a cold front
currently extending from Eau Claire to Mason City, IA washes out
near or just north of the area. A stray afternoon storm is possible
in the vicinity of the decaying boundary, though the majority of the
region will stay dry. A second, better-defined cold front will push
into the Upper Mississippi Valley Tuesday night into Wednesday,
bringing higher chances for scattered storms to at least portions of
southern Wisconsin.

Rest of Overnight: Primary weather impact will be the areas of fog
developing areawide. High-res model guidance has been most adamant
on dense fog potential over the northwest half of the CWA, though
local thinking is that pockets of dense fog will be possible
areawide given broadly favorable conditions in place regionally.
Will thus be monitoring for possible Dense Fog Advisories through
the predawn hours. Slow down, use low beam headlights, and allow for
extra following distance if encountering dense fog on area roads
through daybreak.

Tuesday Afternoon: The remains of a decaying cold front will attempt
to work into northeast Iowa and southwest Wisconsin. How far south
the boundary makes it before stalling and/or washing out remains
uncertain, with the biggest takeaway being that it will bring little
to no relief from the heat & humidity to those in its wake. Thus
anticipating another period of low-mid 90s heat indices areawide,
with heat indices in the upper 90s to near 100 possible in areas
experiencing more sunshine. Not expecting the need for any Heat
Advisories at this time, but will be monitoring trends. Can't
entirely rule out an isolated storm firing near the decaying front
in northeast Iowa/southwest Wisconsin, though weak convergence along
the boundary & very warm 700 mb temperatures/affiliated capping make
this potential low. Nevertheless, westerly steering flow would pull
any isolated storms into locations near and south of I-94 & US-18 if
they occurred, so have introduced some 15% precip probabilities
over southern counties between ~1-7 PM to account for the low
potential. Isolated storms would be capable of producing small
hail and gusty winds if they made it into the area.

Tuesday Night through Wednesday: Will be monitoring for additional
storm chances as a second cold front moves toward the region.
Boundary will roughly extend from southeast Minnesota into north-
central Wisconsin through the overnight hours Tuesday, with an
attendant low level jet response helping to focus areas of shower
and storm activity. Thus anticipate that storm potential will remain
confined to the northwest half of the CWA Tuesday evening & night.
Moving into Wednesday, could see the front and/or any outflow
boundaries affiliated with Tuesday night storms sag toward the
southern half of the state, seemingly providing a focus for at least
isolated storm development areawide. NBM is currently pessimistic
regarding daytime Wednesday precip chances, but have elected to add
some ~15-30% precip probs through the daytime hours given the
potential for surface boundaries to be around. Will need to monitor
for a few strong-severe storms capable of hail or gusty winds in any
storm development occurring Tuesday night into Wednesday.

Quigley

&&

.LONG TERM...
Issued 1210 AM CDT Mon Aug 31 2026

Wednesday night through Monday:

Synopsis: The frontal boundary encroaching during the end of the
short term will linger regionally through the second half of the
work week, ebbing and flowing between stationary to at-times warm
frontal in its behavior. Above normal temperatures & muggy
conditions will thus continue into at least Friday, with afternoon
heat indices in the low to mid 90s remaining commonplace. Similar to
the short term period, heat indices in the upper 90s to near 100
will be possible in locations experiencing prolonged periods of
afternoon sunshine. The lingering surface front & entrenched muggy
air mass will keep conditions active Wednesday night into at least
the first half of the weekend, with periods of off & on
thunderstorms expected to continue. Will need to continue to watch
for a few severe storms, particularly from Wednesday night through
Friday evening.

Wednesday Evening through Saturday: Muggy and active weather
conditions continue as a surface front lingers over the western
Great Lakes. Anticipating similar heat index trends through each
afternoon period, with the more localized nature of any upper 90s to
near 100 degree readings likely precluding the need for any heat
headlines. Will nevertheless be monitoring trends closely, as any
small upward trends would call for reconsideration. Will also be
monitoring for daily storm development. Expecting similar storm
development behavior as the short term through Friday, with a
seasonably strong low level jet supporting bouts of nocturnal storms
& daytime development being contingent on the presence & favorable
placement of surface boundaries. A combination of sufficient deep
layer shear and very high instability will make any storms ones to
watch for severe weather hazards during the Wednesday evening -
Friday time frame. Anticipating more of a transition to disorganized
daytime convection moving into Saturday as both the low level jet &
deep layer shear weaken considerably.

Quigley

&&

.AVIATION...
Issued 550 AM CDT Tue Sep 1 2026

Patchy fog early this morning should remain about the same or
improve over the next couple hours as high clouds continue to
push in from the west. The fog will completely dissipate by mid-
morning after daytime heating kicks in. Not out of the
question for an isolated shower or storm this morning given a
little upstream activity. Otherwise, expect partly cloudy skies
today with VFR conditions likely through the day after the fog
dissipates. Will maintain a small chance for showers and
storms this evening into tonight given the warm, humid, and
unstable airmass.

Light to moderate southwest winds today will become light and
variable tonight into early Wednesday.

DDV

&&

.MARINE...
Issued 1210 AM CDT Mon Aug 31 2026

999 mb low pressure is located near the Ontario-Manitoba border late
this evening, and is forecast to continue eastward toward the
southern Hudson Bay by early Wednesday morning. The low will make
its eastward progression as it fills to near 1008 mb, resulting in
light winds during overnight periods and southerly gusts between 10-
15 knots during the daytime hours. The light overnight winds,
combined with a lingering humid air mass, will support areas of fog
development across Lake Michigan both tonight and Tuesday night.
Whether fog will become dense remains uncertain, with trends being
monitored for Marine Dense Fog Advisories during each overnight
period. Off and on thunderstorms remain forecast through Wednesday
morning as a cold front lingers just to the north of the open
waters. A few storms could be on the strong side with gusty winds
and hail.

Winds will shift east-northeasterly through the second half of the
week as 1020 mb high pressure builds over the Hudson Bay and broad,
1004 mb low pressure moves into the northern Great Plains. An
unsettled pattern featuring multiple additional thunderstorm chances
will continue through at least Friday night. Some storms could be
on the stronger side.

Areas of fog are possible in nearshore zones later tonight as a
muggy air mass lingers across the western Great Lakes. Some dense
fog is possible, with a Dense Fog Advisory now in effect into
Tuesday afternoon. Off and on thunderstorm chances continue through
the end of the week. A few storms could be on the stronger side.

Quigley

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Dense Fog Advisory...LMZ643-LMZ644-LMZ645-LMZ646 until 4 PM
     Tuesday.

     Dense Fog Advisory...LMZ261-LMZ362 until 1 PM Tuesday.

&&

$$

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