NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 110503
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1203 AM CDT Tue Aug 11 2026

.KEY MESSAGES...

- Line of strong to severe thunderstorms will be possible
  across southern WI mid-morning through the early afternoon,
  which will be capable of producing damaging winds and
  localized flooding, especially toward the WI/IL border.

- Additional periodic chances for showers and thunderstorms are
  possible through the midweek.

- End of the week is trending drier with near to below normal
  temps, but a more active pattern is progged to return over the
  weekend.

&&

.SHORT TERM...
Issued 1200 AM CDT Tue Aug 11 2026

Today through Wednesday:

Main focus for the short-term will be an overnight MCS pushing
across southern WI/northern IL mid-morning through the early
afternoon. Already seeing what is progged to be the beginning
of the MCS take shape across the Dakotas. This activity is
expected to continue to develop and expand overnight as it
aligns with a mid- level shortwave trough/vort max. Expect this
complex to track along the west-northwest to east-southeast
orientated theta-E gradient that is currently stretched across
East River of SD through southern MN and into our neck of the
woods.

The biggest question is will this gradient wobble at all
overnight into the early morning as it will be the main driver
of this MCS. The 00z CAMs are hinting at the potential for some
convection to develop through the early morning and may help
shunt the gradient further south toward if not south of the
WI/IL border. If this ends up being the case, then the main part
of the MCS, which would have the stronger cores and capability
of producing severe winds, may skirt to our south with only the
northern part of the line clipping the southern portions of the
CWA. On the other hand, if the boundary remains across a portion
of our area, then would expect the stronger portion of the line
to be more impactful to our CWA.

So will need to monitor trends over the next several hours, but
regardless the potential for strong to severe storm associated
with this MCS will be present thanks to ample SBCAPE (+2000
J/kg) and modest deep layer shear (+40kt) aligning with the mid-
level vort max and low-level frontogenesis/WAA across the
region. As CAMs suggest, there will be potential for bowing
segments with in the line and will be capable of producing
damaging wind gusts of 60-80 mph, but also could not rule out
localized higher gust in the apex of the bows along with an
embedded spin up given the 0-3km bulk shear values of 40-50kt in
a westerly direction. Additionally given the moist and humid
airmass with PWATs exceeding 1.5 inches and even approaching 2
inches, any storms will be efficient rain producers and easily
pick up a quick inch or two resulting in localized flash
flooding. Fortunately this system does look progressive enough
to limit the overall coverage of the flooding concerns to the
strongest cores.

Much of this morning shower and thunderstorm activity is
expected to quickly depart between 18z-20z and will be
predominately dry through the remainder of the day. However,
this stalled front won't be going to far and will linger around
the northern IL region once again into Wednesday. With a
similar pattern and airmass in place, models are showing signs
of another round of mid-morning to early afternoon convection
for Wednesday. Uncertainty remains for this round as it will
depend on where the boundary ends up after prior day's activity
along with if it aligns with additional support from another
mid- level shortwave as the GFS suggests, but other mid-range
models lack. So will continue to monitor.

Wagner

&&

.LONG TERM...
Issued 1200 AM CDT Tue Aug 11 2026

Wednesday night through Monday:

The stationary frontal boundary bringing the active pattern for
the start of the week is expected to gradually sag southward
for the second half of the week. While cannot completely rule
out some lingering shower/storm chances for far southern
portions of our CWA on Thursday, the better upper-level forcing
will gradually slide east as the upper-level low progresses into
Quebec. By Friday, global models have the upper-level ridge
axis build across the Upper Midwest allowing for surface high
pressure to build across the Great Lakes. Thus looking at a
brief break in PoPs for the end of the week along with near to
slightly below normal temps.

However, this quiet stretch will not last as a trough develops
over the central CONUS and slides eastward through the weekend.
GFS and ECMWF along with their ensemble members show a
developing surface low accompanying this upper-level wave.
Expect this low to develop over the Plains for the start of the
weekend and eventually trek eastward later Saturday into early
Sunday. Still plenty of uncertainty on timing and exact track of
the weekend activity, but still a strong and consistent of
enough signal for increased shower and thunderstorm chances for
southern WI during this time.

Wagner

&&

.AVIATION...
Issued 1200 AM CDT Tue Aug 11 2026

A mix of VFR and pockets of MVFR conditions are expected
overnight into the early morning as patchy fog may develop given
the light/calm winds and elevated low-level moisture. This will
likely bring pockets of MVFR or lower visibility and ceilings
through daybreak. Then looking at a line of strong to severe
thunderstorms to roll through mid-morning through the early
afternoon hours. This activity will not only bring heavy
rainfall, lower flight conditions, and lightning, but also
pockets of strong wind gusts, especially for terminal along and
south of I-94. Still expecting this activity to move in as early
as 10-12z west of I-39 corridor and linger through 18-20z for
areas closer to Lake Michigan. Conditions are then expected to
improve behind this round through the afternoon with VFR
conditions prevailing through the evening.

Wagner

&&

.MARINE...
Issued 1200 AM CDT Tue Aug 11 2026

Continue to see light and variable winds across Lake Michigan
as a stationary front remains in place south of the Lake. This
pattern will continue through midweek with periodic shower and
thunderstorm chances for southern portions of the Lake as small
areas of low pressure follow along the stalled front. The front
finally begins to sag southward through the end of the week
allowing high pressure to build down across the Upper Great
Lakes through Friday. Then as the high pressure pushes east
expect low pressure to develop over the Plains and track across
the Great Lakes through the weekend bringing increasing
southerly winds.

Wagner

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Dense Fog Advisory...LMZ643-LMZ644 until 10 AM Tuesday.

&&

$$

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