NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 301137 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
637 AM CDT Sun Aug 30 2026

.KEY MESSAGES...

- Building heat and humidity today through at least the middle
  of the upcoming work week.

- Periods of showers & storms from this morning through early
  Monday morning. Widespread severe weather concerns are low,
  though a few stronger storms with hail and gusty winds are
  possible.

- Storm chances continue Monday evening through at least Tuesday
  night. Some of these storms could produce heavy rainfall & be
  on the stronger side.

&&

.UPDATE...
Issued 637 AM CDT Sun Aug 30 2026

Widespread showers and storms clipping the southeast forecast
area early this morning will wind down towards mid-morning as an
area of stronger warm air advection aloft shifts eastward. There
will likely be a lull in precip most places late morning into
early afternoon.

An area of vorticity currently over northeast Nebraska is
producing showers and storms and is expected to track to
southern Wisconsin today. A couple short term models seem to be
picking up on this and bring widespread showers/storms to the
forecast area by mid-afternoon. Opted to increase precip chances
this afternoon given the current trajectory of this feature
along with some expected instability, decent moisture, and
lingering warm advection aloft. Generally expecting storms to
remain sub-severe through the day, but wouldn't be surprised by
some small hail or gusty winds this afternoon given marginal
instability to go along with 30-40 knots of 0-6 km bulk shear.

Though there will likely be a period of partly cloudy skies mid
morning into early afternoon, decided to lower forecast high
temps a little due to the expected round of clouds and precip
later today.

DDV

&&

.SHORT TERM...
Issued 1040 PM CDT Sat Aug 29 2026

Current Overnight through Sunday night:

Synopsis/Mesoanalysis: A forecast marked by increasing humidity &
conditional chances for showers and thunderstorms prevails through
the short term period. Currently extending from south-central South
Dakota east toward southern Minnesota & the Mississippi River, a
warm front will slowly build toward north-central Wisconsin through
Sunday night. Northeast progression of the boundary will place
southern Wisconsin squarely within a pull of deep warm/moist
advection, with both high temperatures and humidity increasing
considerably for the day Sunday. Periods of showers and storms will
accompany the building heat & humidity, though an absence of large-
scale forcing mechanisms leads to uncertainty regarding coverage &
the exact locations of storm formation. Currently-favored time
periods for storms are during the overnight hours (~midnight &
later) tonight & Sunday night, as well as from late morning into
the afternoon (~11 AM - 5 PM) on Sunday. Widespread severe
weather is unlikely in any activity, though an isolated storm
with gusty winds, small hail, and heavy downpours can't be
entirely ruled out. Keep an eye on the radar through the
remainder of the weekend, particularly if planning to be
outdoors.

Rest of Tonight: Have continued slight chance to chance (~15-40%)
precip probabilities as as an increasing low level jet, warm/moist
advection & affiliated isentropic ascent overspreads southern
Wisconsin. Have been monitoring a broken arc of showers & isolated
thunder from La Crosse toward the Quad Cities through early evening,
which is persisting along the eastern edge of an 850-700 mb thermal
ridge centered over the Missouri Valley. Expect this widely
scattered activity to continue eastward through 1 AM as the thermal
ridge continues to nudge north and east. Will then be monitoring for
additional storm development with greater potential coverage moving
into the predawn hours as the low level jet & affiliated isentropic
ascent reach their overnight maxima. How successful these mechanisms
will be in generating additional storms remains to be seen, as
temperatures will be steadily increasing between 850-700 mb through
the overnight period. As evidenced in 00Z soundings from DVN, ILX,
and MPX, these increasing temperatures will introduce considerable
CIN, even to parcels being lifted from the LLJ (~925-850 mb) level
of the atmosphere. Have thus held precip probabilities to a max
of 40% through the predawn hours, with the highest readings
being centered over the eastern half of the CWA where 850-700 mb
temperatures will remain a touch cooler. Apart from brief heavy
downpours, not anticipating severe weather hazards in any
activity.

Sunday: Will be watching for additional storm development from mid-
day into the afternoon as a weak area of mid-level height falls
tries to work across the Upper Mississippi Valley. Said area of
height falls can be traced to the arc of storms currently ongoing
from north-central South Dakota south into the Nebraska Sandhills.
Assuming a continued track to the east-northeast, crude timing
estimates bring the area of height falls across southern Wisconsin
between ~11 AM - 5 PM Sunday, which has become a preferred time
period for storm development in the arriving suite of 00Z CAM
guidance. Have thus trended ~20-45% precip probabilities toward this
time frame in the evening update, with the understanding that some
adjustments may be needed based on convective trends. Storms will be
capable of producing brief bouts of heavy downpours, though they
should be moving fast enough to keep flooding concerns low. Can't
entirely rule out an isolated stronger storm with gusty winds or
hail, though widespread severe weather potential is low.

Sunday Night: Expecting another round of LLJ-affiliated storm
development regionally. Similar to tonight, very warm 850-700 mb
temperatures & affiliated inhibition leave the east-west coverage of
storms in question, with the best overall storm chances likely to
focus where the LLJ meets modestly cooler values. Currently appears
that this will occur from central Wisconsin toward northern Lake
Michigan, but have maintained chance (~25-50%) precip probs areawide
given lingering uncertainty. Will be monitoring trends and adjusting
as necessary.

Quigley

&&

.LONG TERM...
Issued 1250 AM CDT Sun Aug 30 2026

Monday through Saturday:

Synopsis: Humid & active weather conditions will continue into at
least mid-week as the short term period's warm front becomes cold
frontal & slowly sags south through the state. Slow to at times
stationary boundary speed will keep a warm & humid air mass in place
across the region, which will combine with frontal lift & any
passing impulses aloft to support additional periods of shower and
thunderstorm development through at least Tuesday night. Some storms
will need to be watched for locally heavy rainfall, as well as
severe weather hazards. Frontal boundary evolution from Wednesday
forward becomes less certain, with some solutions pushing the
boundary south of the areas & others keeping it stalled and/or
returning it back north as a warm front. Will be monitoring trends
regarding boundary evolution, as its progression will be the
difference between a continued humid & active pattern versus a
cooler & drier one through the second half of the upcoming work
week.

Monday through Tuesday: Expecting additional bouts of showers and
storms as the slow-moving surface front works through. Relatively
firm consensus across guidance points toward the boundary remaining
draped across the region through the entirety of this time frame,
which makes afternoon/evening shower & thunderstorm chances a good
bet each day. Favorable overlap of abundant instability & sufficient
deep layer shear suggests that more organized storms could
materialize either and/or both days. Will thus need to be watching
closely for severe weather hazards (particularly gusty winds & hail)
during this time frame. Continued elevated precipitable water values
in the 1.5-1.75"+ range would be supportive for heavy downpours in
any storm activity as well. While individual bouts of storms should
be progressive/of low hydrologic impact, will be monitoring for any
signals hinting at training/repeat storm development over the same
areas.

Quigley

&&

.AVIATION...
Issued 637 AM CDT Sun Aug 30 2026

Widespread showers and storms clipping the southeast forecast
area early this morning will wind down towards mid-morning.
There will likely be a lull in precip most places late morning
into early afternoon. There is then increasing confidence in
another round of widespread showers/storms across the forecast
area by mid-afternoon. Generally expecting storms to remain
sub- severe through the day, but wouldn't be surprised by some
small hail or gusty winds this afternoon. VFR conditions should
persist today into Monday, outside of any lower ceilings or
visibilites within thunderstorms.

Breezy southwest winds today will become a little lighter out of
the south tonight, before picking back up from the southwest on
Monday. Low level wind shear will continue through early this
morning and is likely again this evening into Monday morning, as
a low level jet remains overhead.

DDV

&&

.MARINE...
Issued 1250 AM CDT Sun Aug 30 2026

1004 mb low pressure is centered over South Dakota late this
evening, and will continue to drift toward the Mississippi River
through Sunday night. The low will pull a warm front toward the
northern open waters in the process, resulting in a brief period of
breezy southerly winds over the southern half of Lake Michigan
Sunday morning & afternoon. Currently expecting wind gusts to remain
in the 25-30 knot range. Widespread gale potential is low. A new
area of 998 mb low pressure will develop over the Canadian Great
Plains on Monday, steadily progressing into Ontario through Tuesday
as it fills through 1008 mb. Generally southerly winds thus continue
into mid-week across Lake Michigan. Periods of showers and storms
are forecast from the remainder of the overnight hours through at
least Wednesday. A few stronger storms capable of gusty winds and
hail can't be ruled out, particularly during the Monday-Tuesday time
frame.

Southerly winds will become breezy in nearshore zones through the
rest of tonight through Sunday morning as a warm front attempts to
work northeast toward Lake Michigan. Widespread 15 to 20 kt gusts
are anticipated during this time frame, with periods of 25 kt gusts
possible from Milwaukee south to the Winthrop Harbor. Given these
expectations, have thus issued a Small Craft Advisory between 1 AM -
1 PM CDT Sunday from North Point Light south to the Wisconsin-
Illinois border. Will be monitoring trends for any possible
northward expansions through Sunday morning. Periods of showers and
storms continue from the overnight hours through the beginning of
the week. Widespread severe weather isn't anticipated, though an
isolated storm with gusty winds or small hail can't be entirely
ruled out, particularly during the Monday-Tuesday time frame.

Quigley

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory...LMZ645-LMZ646 until 1 PM Sunday.

     Small Craft Advisory...LMZ643-LMZ644 until 5 PM Sunday.

&&

$$

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