845
FXUS63 KMKX 180505
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1205 AM CDT Fri Sep 18 2026

.KEY MESSAGES...

- Brief high swimming risk Friday morning at Milwaukee, Racine,
  and Kenosha County beaches. More prolonged high swimming risk
  expected at all Lake Michigan beaches Friday night through
  the weekend.

- Scattered showers & rumbles during the daytime hours Friday.
  No hazards are expected.

- Widespread showers & storms Friday night into Saturday morning (~10
  PM - 10 AM peak). Locally heavy rainfall and flooding impacts
  are possible. Flood Watch is now in effect over the southwest
  part of the area.

- More showers & storms possible Saturday afternoon & evening. Storms
  could produce additional heavy downpours, though potential
  for flooding impacts is lower compared to Friday
  night/Saturday morning.

- Off & on chances for lighter rain Sunday-Monday. Trending
  drier mid next week.

&&

.SHORT TERM...
Issued 1159 PM CDT Thu Sep 17 2026

Current Overnight through Sunday:

Synopsis/Mesoanalysis: Low stratus clouds and fog pockets are
lingering across parts of southern Wisconsin late this evening as
low level moisture remains stagnant regionally. Already evident in
obs trends over the north-central part of the state, expect that the
responsible moisture will steadily be flushed out through the second
half of the overnight as high pressure builds to the north of Lake
Superior. Said high is forecast to build toward the Ontario-Quebec
border through Saturday morning, maintaining generally easterly flow
across southern Wisconsin. Further west, an upper disturbance is
ejecting into the north-central Plains, with attendant surface
cyclogenesis occurring over northeast Colorado. The newly-forming
surface low will track into the Missouri Valley Friday night,
ultimately moving near or just south of the Wisconsin-Illinois
border on Saturday. A combination of warm advection & frontogenesis
north of the low, in addition to embedded shortwaves in the flow
aloft, will drive two primary periods of showers & storms Friday
night into Saturday morning & Saturday evening/night. Heavy
downpours will be possible in any storms, with locally heavy
rainfall and flooding impacts possible Friday night/Saturday
morning. Severe weather potential is low in all bouts of storms.
Additional lighter showers may continue into Sunday, with minimal
impacts anticipated.

Remainder of Overnight: Will be watching for areas of lingering fog
into the predawn hours. Have carried mentions in the near-term
weather grids, with the thinking being that improvements will
steadily occur toward daybreak with moisture shoving south and winds
attempting to pick up. Warm-advection driven showers & storms
affiliated with the progressing surface low will continue to migrate
eastward toward the Mississippi Valley, but are expected to stay
west of the area through sunrise.

Friday: Continue to expect a brief period of high swimming risk
conditions through the morning hours. A Beach Hazards Statement
remains in effect at Milwaukee, Racine, and Kenosha County beaches
between 7 AM and 2 PM. Exercise extreme caution if heading lakeside,
and be sure to stay away from dangerous areas like breakwaters and
piers. With broad warm advection gradually increasing from west to
east ahead of the approaching surface low, do anticipate that a
scattering of showers & embedded thunder will work into southern
Wisconsin from mid-morning into the afternoon hours. Scattered
precip coverage, along with limited instability, should keep heavy
rainfall concerns minimal in any daytime activity. Keep an eye on
the radar if planning to be outdoors.

Friday evening into Saturday morning: Widespread showers and storms
will move into southern Wisconsin as low pressure makes its
approach. Expect widespread coverage to be maintained through
most or all of this time frame thanks to a seasonably strong low
level jet and attendant conveyor of warm advection in the
925-850 mb layer. Arrival of the low level jet will also bring
an unseasonably moist air mass characterized by precipitable
water values near or slightly above 2 inches (using 00Z OAX RAOB
as a proxy), which will be conducive for enhanced rainfall
rates in embedded convection. Said heavy rates could lead to
nuisance hydro impacts (urban/small stream flooding, ponding of
water, rises on rivers/creeks) areawide, with some potential for
flash flooding in locations where storms track repeatedly. Have
noted run-to-run consistencies in CAM guidance back to 12Z this
morning suggesting that some training will occur, with the
most-favored zone(s) for training likely materializing where the
low level jet intersects with frontogenesis bands in the
925-850 mb layer. Given modeling consistencies and the favorable
environmental factors, have issued a Flood Watch between 1 AM &
1 PM Saturday for the southwest corner of the CWA, where an
overlap of high precipitable waters & LLJ-FGEN intersection is
currently expected to be in place. Have refrained from carrying
the watch any further north or east, as lingering influences
from departing high pressure may impede the most favorable
environmental conditions from progressing beyond the existing
watch area. Will nevertheless be monitoring for changes, as
small changes could call for changes in watch area & start/end
times. Collectively still anticipating 1-3" of rain areawide
during this portion of the period, with higher totals in the
3-5"+ range possible in areas of training (in & near the watch
area).

Saturday evening & night: Will be watching for additional
shower/storm development with the surface low still in the vicinity
& moisture remaining elevated. Could see more heavy downpours in
storms, though current guidance points toward the best potential for
training & flooding hazards over north-central Illinois. Will be
monitoring trends and providing updates as necessary.

Quigley

&&

.LONG TERM...
Issued 1159 PM CDT Thu Sep 17 2026

Sunday night through Thursday:

The east-west surface baroclinic zone is forecast to remain stalled
over northern IL/IN into Monday, with an approaching 500mb shortwave
phasing well enough with it to merit some continued chances for
light rainfall over southern WI. Our positioning north of the
surface boundary ought to limit thunder potential and keep the rain
showers relatively light for Monday.
Predominantly dry weather with only slight chances for rain into
Tuesday as the surface frontal zone sags further south.
Predominantly dry weather should then continue through midweek as
high pressure remains dominant over the region.

The aforementioned 500mb trough from Monday may stall nearby and
close off into a cutoff upper-low midweek next week, a pattern that
often throws a wrench into model predictability. That said, models
have a stable solution on a strong high pressure system over
southern Ontario Canada early next week, shifting east into Quebec
midweek, which leads us to expect a persistent northeast breeze and
cool weather through the period (highs in the 60s, lows around 50).

At the very end of our forecast run (later next week), we begin to
see ridging in the jet, slowly building east into the Upper Midwest.
Temperatures should lean above seasonal norms at some point late
next week into the subsequent weekend.

Sheppard

&&

.AVIATION...
Issued 1159 PM CDT Thu Sep 17 2026

Mix of flight categories prevails late this evening at southern
Wisconsin terminals, with generally MVFR conditions south and VFR
conditions further north. Expect VFR categories to continue
spreading south over the next several hours, with all terminals
expected to be reduction-free by predawn. Could see spotty FG
continue for the next several hours, with mentions being added
as observational trends dictate. Anticipate a brief period of
SCT mid-upper clouds through Friday morning, with mid-level
clouds filling back in during the afternoon hours. Expecting
generally breezy east winds through the remainder of the period
as high pressure passes north of the area & low pressure forms
over the Northern Plains. Winds could be gusty on Friday
afternoon/evening, particularly at the Lake Michigan terminals.
Widespread SHRA & embedded CB will spread in from the west late
Friday afternoon through Friday night. Have inserted prevailing
SHRA mentions at all terminals in the 06Z update given high
confidence for widespread precip development after 00Z Saturday.
Have withheld any mentions of CB for the time-being, but will
be continuing to evaluate for possible mentions in subsequent
forecasts. Expecting CIG & VIS reductions to bring reduced
flight categories with precipitation.

Quigley

&&

.MARINE...
Issued 1159 PM CDT Thu Sep 17 2026

A new area of 1030 mb high pressure will shift from the Canadian
Great Plains into Ontario tonight, maintaining east-northeast winds
across Lake Michigan. 1012 mb low pressure will develop near the
Missouri River Friday afternoon, moving over or just south of waters
during the day on Saturday. Winds will veer east-southeasterly ahead
of the low, becoming gusty at points. A few gusts could approach
gale thresholds, particularly on Friday night and Saturday morning.
Not expecting any borderline gales to be prolonged or widespread
enough to warrant Gale Warnings, but will continue to monitor
trends. Areas of widespread showers & storms will accompany the
approaching/passing area of low pressure Friday night through at
least Saturday night, with widespread severe weather not expected at
this time.

Winds will trend northeasterly Sunday through Monday night as the
aforementioned area of low pressure slowly moves into the Ohio River
Valley. Additional rain showers will accompany the passing low, with
thunder and severe weather hazards appearing unlikely at this time.
1032 mb high pressure will concurrently slide into Ontario from the
Canadian Great Plains, with a compacted pressure gradient allowing
for gusty winds through most of the late weekend/early week time
frame. Similar to Saturday, gusts could occasionally approach gale
thresholds during the Sunday-Monday night time frame, with
conditions not expected to be widespread enough for Gale Warnings at
this time. Winds will steadily taper Tuesday through Wednesday as a
new area of 1026 mb high pressure builds into northern Wisconsin.

A brief period of elevated wave heights is still expected Friday
morning in nearshore zones, with a Small Craft Advisory in effect
between 7 AM and 2 PM from Milwaukee south to Winthrop Harbor. Wave
heights will decrease through the second half of Friday afternoon
and early evening. Gusts and wave heights will increase once more
late Friday evening, and will remain near or above Small Craft
Advisory thresholds through the entirety of the weekend into early
next week. Will be covering this potential with a new Small Craft
Advisory following expiration of the ongoing one Friday afternoon. A
few gusts could occasionally approach gale force during the
prolonged period of advisory conditions, though they are expected to
remain isolated and brief enough to preclude the need for Gale
Warnings. Thunderstorms will move in Friday evening and Saturday
morning, with severe weather not expected.

Quigley

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Flood Watch...WIZ056-WIZ057-WIZ062-WIZ063-WIZ067-WIZ068-
     WIZ069...1 AM Saturday to 1 PM Saturday.

     Beach Hazards Statement...WIZ066-WIZ071-WIZ072...7 AM Friday
     to 2 PM Friday.

LM...Small Craft Advisory...LMZ645-LMZ646...7 AM Friday to 2 PM
     Friday.

&&

$$

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