NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 041900
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
200 PM CDT Thu Jun 4 2026

.KEY MESSAGES...

- Increasing humidity and thunderstorm chances for late tonight
  through Saturday. A 1 out of 5 (marginal) risk for severe
  storms is forecast Friday, but the timing and likelihood of
  the severe potential remains in question.

- Trending less likely for storm chances through the rest of the
  weekend. Not an all day wash out, but can't rule out some
  showers and storms at times.

- Next round of rain is expected early next week.

- Hot and humid conditions expected mid to end of next week

&&

.SHORT TERM...
Issued 200 PM CDT Thu Jun 4 2026

Tonight into Saturday:

The main focus is on the thunderstorm chances through Saturday
as a pair of mid level shortwave troughs propagate through the
Upper Midwest.

Currently, SW to NE oriented frontal boundary region is fairly
evident from the convection that has developed from NW WI down
through central IA and the Omaha area. This forcing is tied to a
mid level shortwave trough currently observed west of this
region which will track east through southern WI tonight into
Friday morning and provide our next chances for rain/storms.
HRRR/RAP has been fairly consistent today with this SW to NE
band of rain/embedded storms to drift east into SW/SC WI until
around midnight. Through the early morning hours Friday, the low
level moisture (925-850mb) transport kicks in and should provide
a secondary surge to the convection and help it to become a bit
more widespread into daybreak. Instability is fairly minimal as
this wave comes through with the 04.17Z RAP showing only a few
hundred J/kg of 0-3km MUCAPE available to be tapped into. The
main question is how much rain will fall given our rapid onset
into drought over the past month. The 04.06/12Z HREF has shown
about 70-100% probabilities of hitting at least 0.25" of rain
across all of southern WI with the more widespread chances of
hitting it going from SW to C WI. Getting between 1 to 2" seems
to be around the high end of the rain potential for this event
which coincides with the higher PWs that will be advected in
with this air mass overnight.

Once this feature/trough tracks off to the east Friday
afternoon, the focus will then go to the north as a secondary
mid level trough currently over Montana which will quickly
propagate eastward into the northern Great Lakes by late Friday.
At the surface, a low should skirt the US/Canadian border as a
cold front drops southeast across Minnesota and northern
Wisconsin. Expect that there'll be some convection that develops
along that feature which could push something through central WI
(Marq/GL/FDL/Sheb co.) in the evening hours. Instability and
shear looks a bit better for this situation, which is what the
Day 2 Marginal risk covers for us. Can't rule something out, but
at this point isn't looking very likely or widespread.

Going into Saturday, still a bit uncertain as the 04.12z
NAM/GFS/EC all show some sort of QPF in southern WI which is
likely tied to that trough/front coming through. Have left some
POPs in there to cover this feature, but overall thinking is
that while we have chances for showers/storms out there that it
won't be an all day rain situation beyond the Friday morning
stuff. Has a bit of a decaying MCV look to it from the
convection that develops in central Iowa early Saturday. Will
have to play this one day at at time right now since what
happens tomorrow will have an impact on the subsequent days.

One thing that does look certain is that it will be more humid
as surface dew points climb into the 60s as the rain moves in
overnight into Friday.

Halbach

&&

.LONG TERM...
Issued 200 PM CDT Thu Jun 4 2026

Saturday night through Thursday:

The main initial focus for any rain/convective development will
be focused along a west to east oriented front set across
southern Iowa into central Illinois on Saturday night. As the
core of the ridge of high pressure drifts east across the Great
Lakes on Sunday, the western wing of this belt will lift
northward as the return southerly low level flow advects a warmer
and more moist air mass back into southwest Wisconsin. Much of
this broad, southerly low level flow is due to a cut off mid
level trough currently observed over northern Mexico which will
get picked up and propagated northeastward through the Plains
into early next week. Some discrepancies exist between the
GEFS/ECMWF for the exact track that this feature takes, but they
all at least pull it northward and should bring the next chances
of rain along with it. Instability is a bit in question along
with weak mid level flow associated with the system, so am not
currently expecting severe potential with it, but details can
change over time and will follow the trends with it.

Beyond that, consensus shows a rather deep and cut off mid level
trough taking hold in the western US putting the Great Lakes
region into the belt of southwesterly mid level flow and strong
low level flow which will bring hot and humid conditions in from
mid week onward. With high temps expected to get into the 90s
and dew points pushing the low 70s, we could be looking at
heat advisory level (HI 100F+) conditions over this period. The
main thing that is uncertain is with those dew points as they
can trend a bit high in the extended period and they may end up
lower.

Halbach

&&

.AVIATION...
Issued 200 PM CDT Thu Jun 4 2026

Main focus for any potential drops from VFR will most likely
come from the band of rain that comes through overnight tonight
into Saturday morning, moreso from ceiling drops. HREF
probabilities generally show a 60-90 percent chance of ceilings
dropping below 3000ft and a 20-40 percent chance of going below
1000ft, mainly between 10-18z Friday morning. Some lighting will
be possible with some brief drops in visibility, but the more
widespread MVFR conditions will be due to ceilings. Conditions
should improve into the afternoon as the system tracks to the
east. Winds will be the gustiest today pushing into the 20kt
range out of the south-southwest before weakening into tonight
and tomorrow as the weak front comes in.

Halbach

&&

.MARINE...
Issued 200 PM CDT Thu Jun 4 2026

Windiest conditions will be today ahead of the front with winds
gusting into the 20-25kt range, which will help bump up waves
into the 6-8 ft range along the western shoreline before the
winds weaken into tonight and Friday. Winds will generally be on
the weaker side through the rest of the weekend before the next
system moves into the western Great Lakes region early next
week.

Halbach

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory...LMZ643...2 PM Thursday to 10 PM
     Thursday.

&&

$$

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