NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 020542
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1242 AM CDT Wed Sep 2 2026

.KEY MESSAGES...

- A few strong thunderstorms with frequent lightning and gusty
  winds possible early this morning, mainly north of WI Hwy 60.

- 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.

&&

.SHORT TERM...
Issued 1240 AM CDT Wed Sep 2 2026

Today and Tonight:

Ongoing convection continues to organize along the MN/IA border,
with a north-south MUCAPE gradient spanning from there all the
way east through southern WI. Our understanding is that this
convection will track east along this instability gradient,
likely moving into portions of central and east-central WI from
3-7 AM this morning, mainly along and north of WI State Trunk
Highway 60 (though some less organized cells could spill further
south). Isolated strong storm cells have already formed across
the northern CWA out ahead of it along the aforementioned
gradient.

The LLJ will undergo nocturnal strengthening, angling
from SW to NE across IA early this morning and feeding into the
approaching MCS as it tracks east towards the Dells. Further
east from there, the LLJ loses its edge, but the MUCAPE remains
in place (and even spreads further north in eastern WI). Most
CAMs allow the MCS to evolve into an MCV (develop a comma head)
as it tracks further east, and though it could begin to decay it
ought to have plenty of system-scale momentum.

We would not be surprised to see a few strong or even severe
storms with this system (level 2 out of 5 severe risk), with the
main threat being damaging wind gusts. Primary threat area is
along and north of Hwy 60 in central and east-central WI, with a
particular emphasis on those areas north and west of Madison. MCVs
have a habit of modifying the environment around them, so stay
tuned in case any of this changes!

The morning storm complex will likely leave an effective outflow
boundary stretching east-west across the CWA, which could serve as
a focal point for some disorganized afternoon showers and
thunderstorms, perhaps reminiscent of what we saw this past
afternoon. The CAPE will be strong, but no features will be
present for substantial storm organization. This will continue to
be the status quo into the evening, with better chances for storm
initiation and coverage late tonight into Thursday AM (continued
in the long-term discussion).

Sheppard

&&

.LONG TERM...
Issued 1240 AM CDT Wed Sep 2 2026

Thursday through Tuesday:

Synopsis: Warm, humid, and unsettled weather is expected to remain
in place through much of the extended forecast, with a slight
signal on some ECMWF/GEFS ensemble plots for a cooling trend
(partial breakdown of the upper ridge) late this weekend into
early next week. The crest of the upper ridge should remain over
or just north of the state, with occasional ripples in the
pattern yielding chances for showers and thunderstorms.

Thursday AM: Though the nose of the LLJ is rather broad across
southern WI predawn through late Thursday morning, ripples in the
700-500mb flow could aid in some convective initiation, and it's
safe to say there is a chance (35-60%) for thunderstorms across
the CWA. Wind shear (30-40kt) is sufficient for some storm
organization if the updrafts can remain robust in the face of
~10 deg-C 700mb temps (would need strong forcing to kick-start
an MCS).

Thursday PM: Some models allow the main surface frontal boundary
(stalled east-west over the upper Great Lakes) to fire convection
Thursday afternoon over the northern half of WI, then plunge it
south into the instability plume (southern half) later in the
day. Though we've got shower and storm chances (10-35%) to
account for this, we'd have to see meaningful forcing for ascent
this far south in order to boost our precip chances any higher,
and right now, we're just not seeing it.

Thursday night into Friday AM: A good fraction of available guidance
hints at a 500mb shortwave descending the eastern crest of the ridge
Thursday night into Friday morning, yielding a round of (potentially
organized) convection across the state. Exact timing is uncertain,
but for now this does yield the strongest wind shear of any feature
on the scope (over 40 kt). If this phases well with lulls / recovery
from the prior round or with the Thursday night LLJ, things could
get interesting.

Sheppard

&&

.AVIATION...
Issued 1240 AM CDT Wed Sep 2 2026

Isolated thunderstorms over central and east-central WI should
gradually increase in coverage through the predawn hours this
morning as a more organized complex (MCS) approaches from the
west. Frequent lightning has been observed, and a few locally
stronger cells with gusty winds and hail are possible. Generally
expecting this activity to remain confined north of WI State
Trunk Highway 60 (includes KSBM TAF). Precip was excluded for
TAF sites further south (aside from PROB30 at KMSN) due to low
confidence, but a stray cell meandering further south in the
state cannot be ruled out. Main timeframe of concern is now
through 7:00 AM.

Later this morning through this afternoon, a few stray showers
or storms possible (similar to last afternoon) along an east-
west outflow boundary kicked out by the aforementioned storms,
but confidence is generally too low for PROB30 levels until
this evening. Cumulus should be fairly high based with this
activity (generally over 5,000 ft), with predominantly VFR
conditions today aside from the storm activity.

Sheppard

&&

.MARINE...
Issued 1240 AM CDT Wed Sep 2 2026

Light winds combined with a lingering humid air mass will
support areas of fog development across Lake Michigan early this
morning, mainly over northern and western portions of the lake.
Off and on rounds of thunderstorms expected today through
Thursday as a stalled front lingers in the region. Widespread
severe weather isn't expected over the waters, though an
isolated stronger cell with hail and gusty winds can't be
entirely ruled out.

Light and variable winds today will shift east-northeasterly
through the second half of the week as 30.1 inch high pressure
builds over the Hudson Bay and broad, 29.6 inch low pressure
moves into the northern Great Plains. An unsettled pattern
featuring multiple additional thunderstorm chances will continue
through at least Friday night.

Sheppard

&&

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

$$

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