NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 171125 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
625 AM CDT Wed Jun 17 2026

.KEY MESSAGES...

- Widespread showers and scattered thunderstorms expected today
  into tonight. Still monitoring a conditional risk for severe
  storms (hail/wind) late afternoon into the evening, though
  the greatest chances will be to the south of the area.

- Locally heavy rain today is still targeting far southern
  Wisconsin near the WI/IL state line.

- A Small Craft Advisory and High Swim Risk are both in effect
  this afternoon through late tonight. Breezy southeast winds
  will lead to high waves and dangerous currents.

- The next substantial chance for thunderstorms arrives Sunday
  (45-65% chances).

&&

.UPDATE...
Issued 625 AM CDT Wed Jun 17 2026

Widespread rainfall with some embedded thunder will continue to
move in from the west early this morning. There remains a chance
for a couple stronger to severe storms later this afternoon
into the evening given enough of a break in precip to allow some
instability to build. Not much has changed in thinking from the
previous forecast discussion for today. The main short term
forecast change that was made was to bump temps down a touch
given the expected widespread precip and clouds. Otherwise, the
forecast looks on track for the remainder of today.

DDV

&&

.SHORT TERM...
Issued 1030 PM CDT Tue Jun 16 2026

Today (Wednesday) and Tonight:

A 500mb trough tracks southeastward across the Dakotas through the
predawn hours this morning, with diffluent flow east of the trough
overspreading IA. Meanwhile, the corresponding surface low
pressure system draws a plume of gulf moisture northward into
IA, igniting an MCS as the dynamics / thermodynamics align. 00z
CAM model guidance tracks this MCS eastward into northern IL /
southern WI with an arrival window of 5-10 AM this morning (from
west to east), and an exit window from ~10 AM to the early-
afternoon. Though our surface winds are forecast to be out of the
southeast in advance of the MCS's arrival, note that we are well
north of the effective warm front (most noticeable in the
surface dewpoint model fields, draped from central IA to central
IL at the time), and all of this convection will be elevated.
With poor mid-level lapse rates and MUCAPE < 1,000 joules, this
initial morning convection should pose practically no severe
threat whatsoever, we'll mainly be watching to see how much
rainfall it can make over southern WI (in advance of the
potentially stronger afternoon / early evening convection); that
and a few rumbles of thunder.

In a similar manner to last Thursday, the parent surface low will
then attempt to lift the effective warm-front further north in IL,
and the closer it gets to southern WI, the stronger our storm
potential will be. The 00z guidance continues to stall the front
well south of the WI/IL border, but depending on which model or
initialization you pick, it could land as far south as I-80 or as
far north as 1-county's distance south of WI (note the 16.21z RAP
Theta-E and wind fields). If the boundary lifts close enough, we
could observe 1,500+ joules of MLCAPE, enough to support hail
or damaging winds with a few storms in the early/mid afternoon
hours. On the other hand, if the boundary lands further south, the
localized heavy rainfall and severe threat over far southern WI
will reduce substantially. The latter scenario may open the door
to late afternoon / early evening airmass recovery...

In the event that clouds can break apart and/or our region can
remain relatively free of convection in the early afternoon,
models like the 17.00z HRRR hint at the potential for the western
half of our CWA to 'recover' to ~1,500 joules MLCAPE and > 7 C/km
mid level lapse rates in advance of the approaching surface low,
which could boost a late afternoon / early evening round of
convection to marginally severe levels, with a weakening trend
further east after the sun sets. Wind gusts and hail would again
be the primary concern.

Sheppard

&&

.LONG TERM...
Issued 1030 PM CDT Tue Jun 16 2026

Thursday through Tuesday:

Predominantly dry weather expected in the cool sector of the
departing low pressure on Thursday. Some lingering 500mb vorticity
on the north edge of the jet, some cool air aloft, and steepening
low-level lapse rates through the course of diurnal heating (below
the subsidence inversion) allows models to yield some slight
chances of cellular rain showers Thursday (~10-20% chance). A
similar story for Friday, not enough jet dynamics to support
much else. Ensemble plots for High Temps suggest a daytime high
around 70 / low 70s for Thursday, with roughly steady state
temperature trends this weekend into early next week.

For Saturday, the longwave upper trough axis accelerates its
eastward propagation, with a brief warm-up to the upper 70s
possible. A developing shortwave ridge in the subtropical jet
(axis from KS into IA) works with the polar jet to rapidly
tighten the geostrophic gradient over WI, resulting in a
strengthening WNW to ESE jet-streak. Precip chances remain
relatively low on Saturday for now (below 20%), but the right-
entrance of this potent jet streak will seed the development of
a strong surface low over the central Plains, which could eject
northeastward towards our region and bring showers +
thunderstorms with it on Sunday (~45-65% chances). Both
ensemble and deterministic systems indicate the preferred system
track would be overhead or south of our region, which would
help to prevent warm sector entry into our region and reduce the
threat of stronger storms. The aforementioned ensemble
temperature plots corroborate this conclusion by keeping
ensemble IQRs for high temps in the low 70s or cooler, as do the
NBM wind fields (E to NE winds off of Lake Michigan on Sunday).
That said, we'll keep a close eye on the track of that system.

If all of this plays out as written, we'd see the surface high
pressure dipole move in for Monday, leaving predominantly dry
weather. Predictability drops for Tuesday, with the ensemble
probability space split between amplifying or deamplifying the
wave train of the jet early to mid next week.

Sheppard

&&

.AVIATION...
Issued 625 AM CDT Wed Jun 17 2026

Widespread rain with some embedded thunder will continue to
spread into the forecast area from the west early this morning.
Ceilings are expected to gradually decrease today as well, with
low ceilings then hanging on into at least early Thursday
morning. Rain will likely transition to scattered showers this
afternoon. Given enough of a break in widespread precip, a
couple strong to severe storms could develop later this
afternoon into the evening. A few showers and rumbles of thunder
may hang on through the evening hours as low pressure moves
through southern Wisconsin, with mainly dry weather likely
overnight into Thursday morning. Isolated showers and storms
will then be possible Thursday afternoon.

Breezy southeast winds will develop by mid to late morning
today, with gusts of 20 to 30 knots likely through the
afternoon. Winds will then shift to westerly this evening and
northwest overnight as the low pushes through.

DDV

&&

.MARINE...
Issued 1030 PM CDT Tue Jun 16 2026

Open Waters / Synopsis:

A light westerly breeze continues into the overnight hours,
decelerating as a weak surface ridge crosses the lake. Winds will
turn south and accelerate Wednesday morning as low pressure around
29.2 inches tracks eastward across southern MN. Winds will turn
southeasterly and become gusty into Wednesday afternoon, with a
few gusts to gale force possible over southern portions of the
lake. The low crosses the lake late Wednesday evening, leaving
gusty west winds over the southern half of the lake Wednesday
night, with a north breeze for the north half. Showers and
thunderstorms are expected across the lake late Wednesday
morning through Wednesday evening. A few strong to severe storms
will be possible over southern portions of the lake Wednesday
afternoon.

Breezy northwest winds are expected through Thursday as the low
pressure system continues eastward. Weaker northwest winds are
then expected to continue into Friday as weak high pressure
around 29.9 inches builds into the midwest.

Nearshore Zones:

The gusty southeast winds ahead of the approaching low pressure
today will result in high waves. A Small Craft Advisory has been
issued this afternoon through late tonight. Expect winds to
veer W / NW after the low pressure passes overhead this evening,
with breezy winds continuing and waves diminishing late
tonight.

Sheppard

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Beach Hazards Statement...WIZ052-WIZ060-WIZ066-WIZ071-
     WIZ072...1 PM Wednesday to 4 AM Thursday.

LM...Small Craft Advisory...LMZ643-LMZ644-LMZ645-LMZ646...1 PM
     Wednesday to 4 AM Thursday.

&&

$$

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