NWS-Milwaukee/Sullivan Forecast Discussion
FXUS63 KMKX 121212
AFDMKX
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
712 AM CDT Wed Aug 12 2026
.KEY MESSAGES...
- Fog is expected through the morning with patchy dense fog
possible in low lying areas and along Lake Michigan.
- Chance for showers and thunderstorms toward the WI/IL border
and toward our central WI counties through this morning with
additional shower and thunderstorm chances on Thursday. Cannot
rule out a stronger storm or two with any of this activity.
- Drier for Friday with an active pattern returning for the
weekend with additional rounds of thunderstorms expected.
- Near normal to below normal temps are expected through the
weekend.
&&
.UPDATE...
Issued 706 AM CDT Wed Aug 12 2026
SPC MesoA continues to show a sharp CAPE gradient to our south
directed from central IA into IL along the Interstate 80
corridor. Its likely that any MCS this morning will follow this
gradient and we may end up completely dry. For now, have
continued slight PoPs along the WI/IL border to account for any
glancing blow from the outer edges of the MCS to our south.
Otherwise the HRRR and RRFS continue to suggest the potential
for scattered storms this afternoon/evening, but disagree on a
definite location. For now, tend to agree the RRFS's placement
over central Wisconsin late this afternoon into the evening,
given a more southward progression to the quasi-stationary
frontal boundary today in the low levels and a logical
progression southward from where storms fired this past night.
CMiller
&&
.SHORT TERM...
Issued 1111 PM CDT Tue Aug 11 2026
Today through Thursday night:
Southern WI continues to sit in between two boundaries, a
surface warm front strewn across Central WI to our north and the
effective warm front with the higher dewpoints/SBCAPE extending
down from northern IA southeastward through IL. This will bring
light and variable winds along with fog across much of southern
WI overnight.
As for shower and thunderstorm chances, the better potential
continues to favor the effective warm front to the south given
the greater instability gradient aligning with the nose of 35 kt
LLJ. Latest thinking is convection upstream across SD/NE into
IA will eventually congeal into another MCS and tap into another
mid-level shortwave trough and track east-southeastward along
the effective warm front through the morning. While the deeper
cores remain south of the WI/IL border, could still see some
showers along the northern peripherals of the MCS clip our
southern tier of counties mid- morning into the early afternoon,
but higher confidence remains to the south.
Additionally, cannot rule out seeing a few isolated to
scattered cells develop north of the effective front as we have
seen over the past couple of nights that may be capable of
producing hail. However, pinpointing if and where anything will
develop remains the question as there is no distinguishable
forcing mechanism at this time, just broad synoptic lift from
700-850 WAA and frontogenesis banding along with 1000-3000 J/KG
of MLCAPE and plenty of CIN. Once the mid-level wave passing
just to our south departs, expect PoP chances to diminishes
through the afternoon with the effective warm front nudging
further south into central IL this evening into Thursday
morning.
Will have another opportunity to see some shower and
thunderstorm chances with this pattern leading into Thursday
morning as another mid-level shortwave trough is expected to
round the base of the slowly moving broader trough through
daybreak. The main difference will be the placement of the
effective warm front well to the south with the great
instability, but will still have the original warm front sag
into our CWA as this wave swings through. This paired with any
lingering upstream convection will be enough to keep increased
PoP chances through mid-Thursday morning into the early
afternoon. Will have to see how things materializes as any
convection may be on a diminishing trend as it moves into
southern WI, but still cannot completely rule out the potential
for pockets of gustier winds if this activity is able to
maintain its strength as it pushes through by the early
afternoon. After this activity, upper-level ridge begins to
build across the Upper Midwest and influence from this activity
pattern shifts away from our area leading to drier conditions
Thursday night.
Wagner
&&
.LONG TERM...
Issued 1111 PM CDT Tue Aug 11 2026
Friday through Tuesday:
Friday continues to trend drier as the influence from the
stationary front that has plagued the region with shower/storm
chances over the past few days moves off as high pressure builds
down the Upper Great Lakes. Looking at near to below normal
temps to accompany a break in the PoPs for the end of the week.
However, a trough is progged to work its way across the
northern Plains into the weekend kicking the ridge axis east.
This pattern will allow for a surface low in the lee of the
Rockies to gradually lift northeastward across the Midwest
through the day Saturday. Expect the low-level WAA and warm
front to spread across southern WI ahead of this incoming system
bringing increased shower and thunderstorm chances earlier
Saturday. Given the latest track, this would then allow for the
leading edge of instability to nudge northward into our neck of
the woods through the afternoon into early evening to support
thunderstorms with any activity that develop ahead and along the
cold front. Currently not favoring strong or severe development
with this round as upper-level jet remains to our north and
lack deep layer shear. However, still plenty of uncertainty in
the low's track, timing, and how far north the higher
instability reaches, but it is not out of the realm of
possibility, just unlikely at this time.
Expect the cold front to slide through either later Saturday
night or on Sunday, which would keep PoP chances around longer.
Nevertheless, expect high pressure and a drier airmass to settle
in later Sunday into the start of next week. Wagner
&&
.AVIATION...
Issued 710 AM CDT Wed Aug 12 2026
Expect fog to linger into the mid morning hours before mixing
out. Low clouds will then persist this morning before gradually
rising and scattering. Storms this morning should stay south of
the WI/IL border. If anything a glancing blow may be dealt to
KJVL and KENW.
Winds will remain light and variable through the TAF period.
CMiller
&&
.MARINE...
Issued 1111 PM CDT Tue Aug 11 2026
Light and variable winds are expected to continue through
Thursday as a stalled frontal boundary remains south of the
Lake bringing periodic shower and thunderstorm chances for
southern portions of Lake Michigan along with patchy fog.
Influence from this front finally moves away from the region as
high pressure builds down across the Great Lakes region Thursday
night into Friday. Will see south to southeasterly winds
increase into the weekend as the high pressure slides east of
the area while low pressure develops over the Plains. Expect
this low pressure to track northeastward across the Upper Great
Lakes later Saturday into Sunday bringing shower and
thunderstorm chances to the Lake. Behind this departing low
pressure, winds shift to the northwest later Sunday into early
next week as another high pressure builds down across the
region.
Wagner
&&
.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Dense Fog Advisory...LMZ643-LMZ644-LMZ645 until noon Wednesday.
&&
$$
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