430
FXUS63 KMKX 160426
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1126 PM CDT Tue Sep 15 2026

.KEY MESSAGES...

- High swim risk Wednesday morning at Milwaukee & Racine County beaches,
  with a moderate swim risk at Ozaukee and Kenosha County
  beaches.

- Isolated sprinkles/showers possible near the Wisconsin-
  Illinois border tonight through Wednesday afternoon, with
  better chances for scattered showers areawide Wednesday night
  into Thursday. No hazards are expected.

- Higher chances for showers & storms arrive Friday-Friday
  night, continuing off & on into early next week. Will be
  watching for locally heavy rainfall Friday through Saturday.

&&

.SHORT TERM...
Issued 930 PM CDT Tue Sep 15 2026

Current Overnight through Thursday night:

Synopsis/Mesoanalysis: A pair of surface fronts are evident over the
Upper Midwest this evening. The southern of the two fronts---which
will linger regionally through the duration of the short term period-
--remains quasi-stationary over central Illinois, and will be a
focus for low level jet-driven convection through tonight. Most if
not all of this precip will stay south of the region. The northern
boundary extends along an approximate Ludington, Michigan - Waukesha
- Janesville line. While more diffuse than its southern counterpart,
a sharp change in air masses occurs across the northern front, with
a much drier Canadian air mass settling in behind it. The northern
front will drop through the rest of southern Wisconsin overnight as
high pressure builds in from the Northern Plains, bringing
noticeably less muggy conditions through daybreak. The high will
continue eastward tomorrow afternoon & night, allowing winds to
trend south-southeasterly regionwide. The larger scale shift in wind
direction will allow the currently stationary southern front to
begin returning north as a warm front. While the boundary is
expected to remain south of the Wisconsin-Illinois border,
increasing low level warm advection will promote scattered shower
development tomorrow night through Thursday morning. A new area of
high pressure will settle into the area Thursday afternoon & night,
keeping conditions dry through the conclusion of the short term
period.

Rest of Overnight: Will be monitoring low level jet-driven
convection in the vicinity of the southern surface front over north-
central Illinois. Current expectations are for strengthening high
pressure over northern Wisconsin to continue funneling drier air
southward, acting to keep the bulk of storms comfortably south of
the CWA. In the event higher moisture lingers along the state line,
an isolated shower or sprinkle would be possible. Have thus
maintained ~10% precip probabilities to the south of I-94 & US-18,
with the expectation that the majority of locations stay dry. No
hazards are expected in the event an isolated shower forms.

Wednesday: Building waves will lead to a high swimming risk at
Racine and Milwaukee County beaches, where a Beach Hazards Statement
is now in effect between 6 AM and 12 PM CDT. Exercise extreme
caution if heading lakeside, and be sure to stay well away from
breakwaters and piers. Small (~10-15%) sprinkle/shower chances will
continue into through the afternoon hours near the Wisconsin-
Illinois border, with hazards not anticipated in any activity.

Wednesday night into Thursday morning: Combination of elevated warm
advection poleward of the southern surface front & lift ahead of a
weak disturbance approaching from the Northern Plains will likely be
sufficient for scattered shower development. Given the broader
nature of increasing forcing, have inserted ~20-40% precip
probabilities areawide, with values gradually contracting toward &
south of the state line as high pressure moves in on Thursday
afternoon. Precip will be ongoing within an unseasonably moist
environment, though a lack of instability in forecast soundings
points toward low potential for enhanced rainfall rates & hydro
impacts at this time. Will continue to monitor for possible changes.

Quigley

&&

.LONG TERM...
Issued 1130 PM CDT Tue Sep 15 2026

Friday through Tuesday:

Synopsis: Mainly seasonable temperatures will prevail through the
long term period, with occasionally muggy conditions mixing in.
Multiple chances for showers and thunderstorms will exist
along/ahead of a pair of passing upper disturbances & affiliated
surface lows & fronts. Currently favored passage windows for peak
forcing & precip potential are Friday through Saturday night &
Sunday through Tuesday. Not expecting showers & storms to be ongoing
for the entirety of either time frame, with intermittent windows of
dry conditions mixing in with the periods of showers and storms.
Will continue to refine timing details over coming updates. An
unseasonably moist environment will accompany storm development
during the Friday-Saturday night time frame, with locally heavy
rainfall possible in locations experiencing multiple batches of
shower/storm activity. Where any such locally heavy rainfall may
occur, and how widespread its occurrence may be, remains uncertain
this far out, with trends being monitored through the second half of
this week.

Friday through Saturday night: Showers & storms will likely be
ongoing near or just to the west of the region Friday morning
following the arrival of an upper disturbance & attendant surface
cyclogenesis in the Northern Plains Thursday night. With the low
continuing into the Upper Mississippi Valley on Friday, suspect that
at least scattered shower and storm potential will try to spread
east into southern Wisconsin during the morning & afternoon hours
Friday. Global ensembles point toward very marginal instability
through Friday afternoon, implying minimal strong/severe potential
in any of this activity. Brief heavy downpours would be possible
given steadily increasing precipitable water values. If current
timing trends hold, more favorable ingredients for possible locally
heavy rainfall would begin to align overnight Friday into Saturday
morning, when a deep pull of warm/moist advection would bring even
higher precipitable water values into the area as the low level jet
concurrently triggers additional storm development. Whether
ingredients will come together to realize locally heavy rainfall
will depend on storm-scale details (namely training), which will
clarify with the arrival of high-res guidance later this week. Could
then see additional storm potential along a passing cold front
Saturday afternoon/evening, with favored locations for redevelopment
being dependent on still unclear boundary positioning. Will be
monitoring position trends over coming updates.

Sunday through Tuesday: Second disturbance will move across the area
from the Northern Plains, interacting with the weekend frontal
boundary to support additional chances for showers and a few storms.
Large spread in frontal location & upper disturbance track make it
difficult to offer additional details regarding timing or the
potential for additional heavy downpours at this time, with details
expected to clarify as this portion of the period draws closer.

Quigley

&&

.AVIATION...
Issued 930 PM CDT Tue Sep 15 2026

Mostly VFR flight categories prevail through the remainder of this
evening through the day Wednesday. Observed earlier in the evening
near the Wisconsin-Illinois border, -RA & MVFR CIG potential will
shunt south of the state line through the remainder of tonight. High
pressure will continue to nudge into northern Wisconsin tonight,
bringing a north-northeast wind shift at all terminals. The high
will continue east through Wednesday, bringing an east-southeast
wind shift by mid-late afternoon. Warm advection will increase
regionally Wednesday evening, with gradually-lowering CIGs
eventually leading to at least MVFR conditions overnight. Rain
showers may accompany the lowering CIGs. Have accounted for this
potential with PROB30 groups at all aerodromes, with the need for
TEMPO and/or prevailing mentions being assessed through
tomorrow.

Quigley

&&

.MARINE...
Issued 1130 PM CDT Tue Sep 15 2026

1022 mb high pressure is building into the Upper Mississippi Valley
late this evening, allowing winds to shift out of the northwest
across the open waters. The high will continue east across northern
Lake Michigan Wednesday morning, quickly moving toward the Ontario-
Quebec border Wednesday night into Thursday. Progression of the high
will allow winds to trend east-northeasterly Wednesday through
Thursday morning. Occasional periods of showers and thunderstorms
will continue into Thursday, with severe weather not expected.

A new area of 1030 mb high pressure will shift from the Canadian
Great Plains into Ontario Thursday night into Friday morning,
maintaining east-northeast winds across Lake Michigan. 1012 mb high
pressure will develop near the Missouri River Friday afternoon,
moving over or just south of the waters during the day on
Saturday. Winds will veer east-southeasterly ahead of the low,
becoming gusty at points. Some gusts could approach gale
thresholds, particularly on Friday night and Saturday morning.
Whether borderline gales will be widespread enough to warrant
Gale Warnings remains uncertain at this time, with trends being
monitored through the end of the week. Areas of widespread
showers & storms will accompany the approaching/passing area of
low pressure Friday night through Saturday, with widespread
severe weather not expected at this time. Winds will trend
northeasterly as the low moves into the Ohio River Valley
Saturday night into Monday.

Wave heights will increase for a brief time period Wednesday morning
in nearshore zones. A Small Craft Advisory is in now in effect
between 6 AM - 12 PM CDT from Port Washington south to Winthrop
Harbor. Wave heights will taper Wednesday afternoon. An additional,
more prolonged period of Small Craft Advisory conditions is
anticipated Friday afternoon through Monday as a storm system moves
through the Upper Midwest. Anticipate that headlines will become
necessary as this portion of the period draws closer. Could see a
few gale force gusts during the Friday-Monday time frame, though any
such gusts are currently expected to remain isolated and brief
enough to preclude the need for Gale Warnings. Will nevertheless be
monitoring for possible changes through the end of the week.

Quigley

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Beach Hazards Statement...WIZ066-WIZ071...6 AM Wednesday to
     noon Wednesday.

LM...Small Craft Advisory...LMZ644-LMZ645-LMZ646...6 AM Wednesday
     to noon Wednesday.

&&

$$

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