NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 090109 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
809 PM CDT Tue Sep 8 2026

.KEY MESSAGES...

- Moderate swim risk at Ozaukee & Sheboygan County beaches this
  evening. Stay away from breakwaters and piers if planning to
  be in the water.

- Periods of off/on showers with a chance of thunderstorms
  continue through tonight. Storms could produce locally heavy
  rainfall.

- Warm temperatures with low humidity through the second half of
  the work week. Shower and storms return to the forecast Friday
  night into Saturday.

&&

.UPDATE...
Issued 809 PM CDT Tue Sep 8 2026

Light rain showers are spreading into south central WI this
evening. These are elevated and without lightning since the
instability axis is lagging behind in south central MN and Iowa
right now.

The area of strongest storms is over central Iowa and that will
continue to dive southeastward along the theta-e gradient and
also the instability gradient. Southern WI will continue to be
in the stratiform rain region. There will be increasing
precipitable water values which will bring lower cloud bases
and deeper moisture. A southwest to west low level jet will push
into south central WI already late this evening but then shift
south (out of WI) after 4 AM. This is also coincident with a
weak 500mb shortwave trough. The LLJ will help trigger more
widespread showers and give us a little chance for a few rumbles
of thunder tonight.

Given that we are not expecting deep convection tonight, the
flooding risk is pretty low. However, it still looks like all
but central WI has a high chance (80%) of seeing a soaking rain
with amounts up to a half inch. Locally higher amounts up to an
inch will be possible, especially toward the IL border.

Showers will end from northwest to southeast through mid
Wednesday morning.

Cronce

&&

.SHORT TERM...
Issued 150 PM CDT Tue Sep 8 2026

Rest of this Afternoon through Friday:

Synopsis/Mesoanalysis: Low pressure is centered over central
Manitoba this afternoon, with an attendant cold front extending from
the Manitoba-Saskatchewan border south toward the Sioux Falls, SD
vicinity. A muddy prefrontal warm sector is apparent regionally,
with areas of showers and embedded thunderstorms ongoing from
Sheboygan southwest to the Missouri River. Activity is ongoing
within steady warm advection north & east of a warm front currently
extending from Des Moines to near St Louis. Both the warm & cold
fronts will work their way toward and into southern Wisconsin this
evening into Wednesday morning, bringing continuing chances for on
and off showers and storms. Some storms could produce isolated gusty
winds and locally heavy rainfall. The approaching cold front will
push southeast of the area by Wednesday afternoon, with high
pressure settling into the western Great Lakes Wednesday night
through the day on Friday. The arriving high will maintain pleasant
& warm conditions with low humidity through the end of the work
week.

Rest of this Afternoon: On and off showers and thunderstorms will
continue areawide. Storms could produce a few flashes of lightning &
brief heavy downpours, although scattered coverage & limited
residence time will keep locally heavy rainfall concerns low. With
better instability still lagging to the west of the region, not
expecting any severe weather hazards in storms. Keep an eye on the
radar if planning to be outside. Increasing wave heights will lead
to a moderate swim risk at Sheboygan and Ozaukee County beaches.
Exercise extreme caution if heading lakeside in these locations.

Tonight into Wednesday morning: Moderate swimming risk continues
through mid-evening (~9 PM) at Sheboygan and Ozaukee County beaches.
Anticipating a steady southwest-northeast uptick in showers and
storms near & after 12 AM as cold frontal and low level jet-
affiliated forcing spread into southern Wisconsin. Increasing storm
coverage could begin a touch earlier (~9 PM-midnight) west of I-39 &
a touch later (midnight-3 AM) further east. Modestly higher
instability will be arriving into southern Wisconsin during this
time frame, so greater embedded thunderstorm coverage is anticipated
relative to this afternoon's showery activity. As evidenced by
upstream 12Z soundings from MPX & SGF, an unseasonably moist air
mass characterized by 1.75"+ precipitable water values will also be
arriving, which will help to support brief periods of enhanced
rainfall rates within storms. Thus expecting a general 0.1-0.5"
rainfall areawide, with areas to the west of I-39 most likely to see
the higher accumulations. Front-parallel steering flow points toward
some potential for brief periods of training & affiliated locally
higher totals in the 1-2"+ range. Best potential for these locally
higher totals will be over the southern half of the area. Could see
some minor hydro impacts (ponding of water, urban & small stream
flooding) in areas of localized training, though widespread flash
flooding potential is low. An isolated stronger storm with gusty
winds can't be ruled out, though more widespread severe weather
potential is expected to remain well southwest of the area.

Quigley

&&

.LONG TERM...
Issued 150 PM CDT Tue Sep 8 2026

Friday night through Tuesday:

Synopsis: Near or slightly above normal temperatures are expected
through the duration of the long term period. A pair of upper
disturbances are progged to move through the western Great Lakes
Saturday-Saturday night & Monday-Monday night, providing larger
scale forcing for periods of showers & embedded thunderstorms. Each
disturbance will be accompanied by an affiliated pairing of surface
warm & cold fronts, with seasonably muggy conditions anticipated in
the warm sectors building in between the boundaries. Currently
looking at the highest humidities being on Saturday
afternoon/evening & Monday afternoon/evening, when southern
Wisconsin is forecast to be each in each respective warm sector. Not
anticipating humidity reaching heat headline-level thresholds during
either period.

Friday night through Saturday night: First of two upper disturbances
will cross southern Wisconsin, bringing periods of showers and
thunderstorms. Expecting an initial wave of activity Friday night
into early Saturday morning as a warm front & affiliated warm/moist
advection overspread the area, with more precip development possible
Saturday afternoon/evening along the trailing cold front. Saturday
afternoon/evening storm development will be contingent on sufficient
sunshine & thermodynamic recovery in the wake of overnight/early
morning activity, with more details becoming apparent as finer scale
model guidance arrives later in the week. Raw shear and precipitable
water values point toward some potential for organized storms with
heavy downpours in any development, though whether or not favorable
parameters will be realized remains to be seen. Will be watching
trends through the end of the week and providing updates.

Sunday night through Monday night: Next window of shower and storm
potential arrives ahead of the next upper disturbance. Expecting
similar system evolution to Friday night-Saturday night, with an
initial batch of warm advection showers & storms Sunday night/early
Monday morning & cold frontal redevelopment Monday
afternoon/evening. Like the weekend system, global ensembles point
toward sufficient deep layer shear & precipitable water values for
more organized storms with heavy downpours, with the realization of
favorable environmental conditions being dependent on still
uncertain thermodynamics. Will be providing updates as trends
clarify.

Quigley

&&

.AVIATION...
Issued 809 PM CDT Tue Sep 8 2026

See the main Area Forecast Discussion for precip details. The
main window of showers will be between 04Z (11PM) and 09Z (4AM),
but lighter rain should spread in a little earlier and there is
a chance of a few trailing showers in the morning. A period of
MVFR ceilings with bases around 2500 feet (down to 1500 ft
possible) is likely early Wednesday morning. Look for precip and
low clouds to end from west to east late Wed morning and
potentially into early Wed afternoon.

Cronce

&&

.MARINE...
Issued 150 PM CDT Tue Sep 8 2026

Southerly winds will increase into tonight over Lake Michigan as 998
mb low pressure shifts toward the Hudson Bay from the Canadian Great
Plains. A cold front will move across Lake Michigan on Wednesday,
bringing a generally westerly wind shift across the lake. Periods of
showers and occasional thunderstorms will accompany the
approaching/passing surface front this afternoon through Wednesday
morning. Severe weather isn't expected.

A new area of 1020 mb high pressure will move from the northern
Great Plains across Lake Michigan Wednesday night through Thursday
night, bringing a period of light and variable winds to the waters.
The next area of 992 mb low pressure will shift from the Canadian
Great Plains across the Hudson Bay Friday afternoon through Saturday
night, bringing increasing southwest winds. A few gale force gusts
are possible during this time frame, particularly over the northern
third of Lake Michigan. Will be monitoring trends through late week
for possible headlines. A cold front will move over Lake Michigan
Sunday morning, bringing a northwest wind shift to the waters.

Occasional wind gusts approaching Small Craft Advisory thresholds
are possible through this evening to the north of Port Washington.
Have held off on any headlines in the afternoon update given an
expected brief & isolated nature to any such conditions, but will
nevertheless continue to watch trends. Scattered shower and
thunderstorm chances will continue through early Wednesday morning
in advance of an approaching cold front, with severe weather not
anticipated. Periods of Small Craft Advisory conditions are possible
Friday into Saturday & early next week, with trends being monitored
for headlines over coming forecasts.

Quigley

&&

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

$$

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