006
FXUS63 KMKX 182017 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
317 PM CDT Fri Sep 18 2026

.KEY MESSAGES...

- Widespread showers and storms this afternoon through Saturday
  morning (10 PM to 10 AM peak). Widespread 1-3 inches with a
  band of 3-5 inches of heavy rainfall and flooding impacts are
  expected. Pockets of locally higher rainfall greater than 5
  inches will be possible. A Flood Watch remains and has been
  expanded for all southern WI.

- Additional showers and storms possible Saturday afternoon and
  evening. Storms could produce stronger storms and additional
  heavy downpours, though potential for flooding impacts is
  lower compared to tonight and Saturday morning round.

- High swim risk and small craft conditions expected tonight
  through Saturday. Additional elevated swim risk conditions
  possible on Sunday.

- Off and on chances for lighter rain for start of next week
  and trending drier toward the middle of next week.

&&

.SHORT TERM...
Issued 311 PM CDT Fri Sep 18 2026

Tonight through Sunday:

A wet start to the weekend ahead. Southern WI is looking at a
prolonged period of moderate to heavy rainfall as low pressure
over the Plains lift northeast into the Midwest. Low-level WAA
and frontogenesis band ahead of this low will continually spread
into the southern WI now through tonight. Already seeing some
light rain on the leading edge of this forcing, but expecting
this activity to ramp up later this evening into Saturday
morning as PWATs approach/even exceed 2 inches align with low-
level frontogenesis, WAA, and nose of a 30-40 kt LLJ. Additional
periods of moderate to heavy rainfall and even some
thunderstorms are expected at least for the southern half of the
CWA through Saturday afternoon/evening as the surface low lifts
across IA/MO to IL/southern WI. Rain chances are then expected
to diminish into Sunday as the low tracks east and a strong high
pressure builds over the Great Lakes bringing prevailing
northeasterly flow and cooler temps to the area.

Heavy Rainfall Tonight into Saturday Morning: Consistent signal for
widespread 1-3 inches of rainfall with a band of 3-6 inches or more
to impact our area tonight through Saturday. A bulk of this rain is
expected overnight into Saturday morning. The 12z HREF and REF
guidance are in fairly consistent agreement with the heaviest
band to setting up from west-northwest to east-southeast across
the central portion of our CWA following the 10-20kt Corfidi
vectors. Expecting 12hr totals of 2-4 inches or more within the
heaviest band. This will be the area that has the greatest areal
flooding and ponding potential especially for urban and low-
lying areas given the more prolonged nature of the rainfall.
However could still see pockets of 0.5-0.75 in/hr rates with
any thunderstorms and if they move over the same area that has
already seen plenty of rainfall, then this could result in flash
flooding concerns. Thus have expanded the Flood Watch to
include all of southern WI. However, will need to monitor where
the rainfall persists and set ups overnight.

While there is a general consensus and good agreement on this
taking shape over our CWA, the heaviest rainfall band may
wobble from the latest forecast as it will depend on where the
frontogenesis band sets up. Have seen these wobbles with the
previous runs of the CAMs, and a 10-20 mile wobble may result in
a few inches of rainfall versus several inches. Thus, still
some play on exactly where the heaviest rainfall will setup and
move over the same area. Again any urban areas that experience
heavier rates and thunderstorms will be more susceptible to
flash flooding tonight into Saturday morning than rural areas.

Expecting this round to wind down later Saturday morning as we loose
the LLJ and additionally upper level support while the frontal
boundary sags south. Thus may just see some light to occasional
moderate rainfall linger for the later morning and early
afternoon especially for areas closer to the WI/IL border.

Saturday Afternoon/Evening Rainfall and Thunderstorm Potential:
After the brief reprieve for the morning round, eyes turn to
redevelopment and even better thunderstorm potential for Saturday
Afternoon and evening. This activity will be more dependent on the
track of the surface low and if/how far north the frontal boundary
lifts back into our area. Models that favor a more northern track of
the low, such as the NAM and HRRR will allow for temps to warm into
the mid to upper 70s, moisture return with dewpoints into the upper
60s and low 70s, and instability to building to 1000-1500 J/kg. Pair
this with a warm frontal boundary and +45kt of deep layer shear and
cannot rule out seeing stronger to even a few severe thunderstorms
develop with all severe hazards possible. Will also be additional
chances for localized heavy rainfall associated with any of this
convection further increasing rainfall totals and resulting in more
of a flash flood potential given the previous round of rain.
However, this scenario will be highly dependent not only on the low
track and front placement, but also if the morning rain will exit
earlier allowing for the environment to recover and anything that
does get going able to break the cap.

The other scenario will be the front shifts south through the
morning and the low tracks more across IL than WI keeping southern
WI on the cool side of the system. Still could see a few
isolated stronger storms develop tapping into the elevated
instability bringing some hail, but the more favorable temps and
dewpoints remains south of our CWA. Nevertheless, this could
bring additional rainfall over areas that seen heavy rainfall,
especially toward the WI/IL border with the previous round of
activity. Otherwise should see shower and storm activity
diminish through Saturday night into Sunday as the low shifts
east and the front sags south again with the building high
pressure.

Lastly, with persistent and increasing onshore winds building
waves up 4-7 ft tonight through Saturday, expecting high swim
risk conditions to redevelop resulting in dangerous currents for
all southern WI beaches.

Wagner

&&

.LONG TERM...
Issued 311 PM CDT Fri Sep 18 2026

Monday through Friday:

Monday is trending not as wet compared to the weekend as the
frontal boundary sags south and stalls across IL/IN. Models do
prog drier and cooler airmass to try and migrate into southern
WI through the start of next week. However, given the frontal
boundary placement along with globals models showing an upper-
level trough swinging through the region, thinking there will be
off and on light showers/drizzle through the start of the week
not too dissimilar to what we saw from the middle of this past
week. The main trough is expected to swing across the Midwest on
Tuesday with the the frontal placement being the main driver of
rainfall amounts. Given the latest model trends, thinking it
will be more of light and dreary start of the week for southern
WI as this activity will compete with a +1030mb high along and
just north of the Great Lakes region. Still will need to monitor
and see where the front stalls as a northern jog in the
boundary or the surface high, could result in more moderate
rainfall creeping back north into the area, but will continue to
monitor trends.

Otherwise, upper-level ridge is progged to build across the Midwest
along with the surface high across the Great Lakes/eastern Canada
through middle of next week. This will bring a drier airmass and
northeasterly flow to the area. However, may see more sunshine and a
southerly shift in winds toward the end of the, which may bring a
bit warmer temps to southern WI.

Wagner

&&

.AVIATION...
Issued 311 PM CDT Fri Sep 18 2026

Easterly winds have become more prominent today and will
continue tonight into Saturday morning. The main aviation
concern this evening will be the lower flight conditions from
increasing moderate to heavy rainfall overnight into Saturday
morning. Expecting widespread 1-3 inches of rainfall with a band
of heavier rain seeing 3-5 inches and even pockets of more than
6 inches possible. Accompanying this activity will be MVFR to
LIFR ceilings below 1500 ft and visibilities of 1-4 sm or less
at times. Could also hear a few rumbles of thunder especially
for terminal closer to the WI/IL border. Will see this shower
activity linger through midmorning before lessening into the
early afternoon. However, lower ceiling are looking to linger
longer. Then additional shower and thunderstorm chances return,
especially for terminals along and south of I-94 later Saturday
afternoon and evening.

Wagner

&&

.MARINE...
Issued 311 PM CDT Fri Sep 18 2026

Low pressure over the Missouri River this afternoon will track over
or just south of the waters during the day on Saturday. Winds will
veer east-southeasterly ahead of the low, becoming gusty at times. A
few gusts could briefly approach gales, particularly tonight and
Saturday morning. However, small craft conditions are expected for
southern WI nearshores again tonight through Saturday. Areas of
widespread showers and thunderstorms will accompany the passing area
of low pressure tonight through at least Saturday night.

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. High
pressure will concurrently slide into Ontario from the Canadian
Great Plains, with gusty winds expected through most of the late
weekend to early week time frame. Similar to Saturday, gusts could
occasionally approach gale thresholds during the Sunday into Monday
night time frame. Winds will steadily taper Tuesday through
Wednesday, as a new area of high pressure builds into northern
Wisconsin.

Wagner

&&

.HYDROLOGY...
Issued 311 PM CDT Fri Sep 18 2026

Localized flooding and river rises are expected where the heaviest
rainfall occurs. With 1 to 3 inches across much of the area over the
next 24 hours, ensemble river forecasts show roughly a 20% chance
rivers may exceed minor flood stage and about a 10% chance rivers
may exceed moderate flood stage. However, a band of locally higher
rainfall (amounts of 4 to 6 inches or more possible), increases
river flooding chances in those areas hardest hit or any areas with
repeated rounds of highest rainfall rates. Additional rainfall
for far southern Wisconsin on Saturday night may prolong or
cause additional river rises. Streamflow across southern
Wisconsin is normal to below normal, in the 20th-60th
percentile, so there is some room contain the rainfall, lowering
chances of reaching major flood stage.

Marquardt

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Beach Hazards Statement...WIZ052-WIZ060-WIZ066-WIZ071-
     WIZ072...10 PM Friday to 1 AM Sunday.

     Flood Watch...WIZ046-WIZ047-WIZ051-WIZ052-WIZ056-WIZ057-WIZ058-
     WIZ059-WIZ060-WIZ062-WIZ063-WIZ064-WIZ065-WIZ066-WIZ067-
     WIZ068-WIZ069-WIZ070-WIZ071-WIZ072...1 AM Saturday to 1
     PM Saturday.

LM...Small Craft Advisory...LMZ643-LMZ644-LMZ645-LMZ646...10 PM
     Friday to 1 AM Sunday.

&&

$$

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