NWS-Milwaukee/Sullivan Forecast Discussion
FXUS63 KMKX 120005
AFDMKX
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
705 PM CDT Tue Aug 11 2026
.KEY MESSAGES...
- Chance for showers and thunderstorms along the WI/IL border
tonight and into Wednesday with additional shower and
thunderstorm chances on Thursday, but severe weather is not
expected at this time.
- Fog is expected tonight, with patchy dense fog possible in low
lying areas and along Lake Michigan.
- Drier for Friday with an active pattern returning for the
weekend with multiple rounds of thunderstorms expected.
- Near normal to below normal temperatures expected through the
end of the week and through the weekend.
&&
.UPDATE...
Issued 655 PM CDT Tue Aug 11 2026
Southern WI sits 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
IA southeastward through IL. The effective warm front has been
the main focus for convection over the past few days and will
once again be the focus for more robust development overnight
into Wednesday morning. However, earlier convection has helped
it push south, but could still see some of this activity creep
north of the front toward the WI/IL border through the overnight
into Wednesday morning especially as a mid-level shortwave
trough passes through the area.
While it has not be as active, the warm front to the north will
bear watching as well this evening. As suggested by CAMs and
latest radar trends, could see a few showers and storms pop
along this feature and make their way into our central WI
counties this evening/tonight, but lack of trigger as well as
building CIN will be some limiting factors for this activity.
Otherwise, given the light winds and ample low-level moisture
hanging around the area, expect to see fog develop overnight
through the morning hours. Low-lying areas and along Lake
Michigan Lakeshore will see some of the lowest visibilities and
may see periods of dense fog at times as well.
Wagner
&&
.SHORT TERM...
Issued 141 PM CDT Tue Aug 11 2026
Tonight through Wednesday night:
Isolated to scattered thunderstorms possible this afternoon
through tonight across far southern Wisconsin as a weak
stationary front remains draped along the WI/IL border.
Generally zonal flow in the jet stream level will allow for
fast-moving shortwaves along the frontal boundary to produce
locally enhanced thunderstorm activity. Due to the diffuse
nature of the forcing, not expecting any widespread strong
thunderstorms. However, can't rule out an isolated stronger
storm right along the frontal boundary with MUCAPE around 2500
J/kg along and south of the I-94 corridor. Westerly bulk shear
around 45-50 kt will continue across the region through
Wednesday as well, giving sustenance to storms that do tap into
the higher MUCAPE and develop.
A stronger shortwave ejecting from the Canadian High Plains
phases with the stationary front across the central Plains
overnight Wednesday. This serves as a focal point for the
strongest-forced storms of the next few days, with PoPs
increasing into Thursday morning as the shortwave approaches.
Plenty of moisture (PWATs ~1.5 inches) combined with the
stronger shortwave indicates more confidence in widespread
thunderstorm coverage going into Thursday morning.
Outside of precipitation chances, expecting temperatures to
remain in the normal to below normal range (highs in the low
80s, lows in the low to mid 60s) throughout the short term
forecast window as the stationary front keeps the warmest
conditions just south of the border. Overnight, with lingering
high dewpoints near the frontal boundary and calming winds,
expect widespread fog development. Patchy dense fog is possible
in low-lying areas and near Lake Michigan.
MH
&&
.LONG TERM...
Issued 141 PM CDT Tue Aug 11 2026
Thursday through Tuesday:
Low pressure deepens over the central Plains on Thursday, with a
remnant baroclinic / frontal zone oriented NW to SE across the
midwest. Precip chances range from 20-70% across the CWA Thursday
(highest towards the southwest corner of Wisconsin), with at least 1
minor shortwave providing some potential triggering for convection.
Thunderstorms would likely be weak if applicable, given the lack of
return flow ahead of the low. The true warm sector appears to remain
well south into Illinois.
Predominantly dry weather expected into Friday as high pressure
builds into the Great Lakes region. As weak low pressure tracks
eastward across the midwest, showers and thunderstorms are looking
likely at times from Friday night through Saturday night, with
lingering 20-30% chances into Sunday as the associated cold front
swings through. Passing high pressure may then lead to predominantly
dry weather into Monday.
Temperatures should remain mild through the entire forecast period,
lingering around seasonal norms or even slightly cooler.
Sheppard
&&
.AVIATION...
Issued 659 PM CDT Tue Aug 11 2026
VFR conditions persist through the remainder of the evening, but
expecting widespread fog to develop across southern WI overnight
into Wednesday morning. Expect MVFR to LIFR conditions with any
fog development as winds remain light to calm paired with
elevated surface moisture. Low-lying areas as well as for
terminals closer to and along Lake Michigan lakeshore could see
periods of dense fog at times through daybreak. Visibility are
expected to improve between 12-14z as temps warm and dewpoint
depression increase. But light and variable winds are expected
through much of the day Wednesday as well. As for shower and
thunderstorm potential, there is not as much of a chance
tonight as previous nights with the focus for this development
sitting south across IL and a weaker area to the north across
central WI. Nevertheless, will need to keep an eye as a few
scattered showers and storms could pop up along these boundaries
later this evening through Wednesday morning, just do not have
confidence that it will impact any southern WI terminals at this
point.
Wagner
&&
.MARINE...
Issued 141 PM CDT Tue Aug 11 2026
Predominantly light and variable winds are expected to continue
today through Thursday, with periodic chances for showers and
thunderstorms for the southern third of the lake (near a stalled
frontal boundary). Patchy fog is also possible along and south
of the frontal boundary.
High pressure around 30.3 inches builds into the Great Lakes region
Thursday night, resulting in a 10 to 20 kt northeast breeze across
Lake Michigan and pushing the frontal boundary south of the lake.
These winds will continue into Friday, with dry weather expected.
Winds veer southeast and accelerate into Saturday as high pressure
shifts over the lower Great Lakes and low pressure lifts northeast
from the central Plains. This system will bring chances for showers
and thunderstorms at times Saturday morning through Sunday morning.
Decelerating northwest winds expected into early next week behind
the associated cold front.
Sheppard
&&
.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...None.
&&
$$
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