NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 090036
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
736 PM CDT Sat Aug 8 2026

.KEY MESSAGES...

- Dry and pleasant today with highs in the low 80s.

- Thunderstorm chances return Sunday. There is the potential for
  a late morning to afternoon round, and then an evening and
  overnight round. Strong to severe storms will be possible.
  Uncertainty remains regarding exact timing of the rounds and
  positioning.

- Any storms on Sunday will be capable of heavy rain. Localized
  flooding will be possible, especially where storms repeatedly
  track through the day.

- Multiple rounds of rain and thunderstorms are possible through
  the work week.


&&

.UPDATE...
Issued 730 PM CDT Sat Aug 8 2026

High pressure is moving east through IA and northern IL this
evening. This will keep conditions quiet through the rest of the
evening into early tonight. As the night wears on, the LLJ is
expected to nose into southern Wisconsin with southwest winds
and WAA kicking in during the early morning hours. With bulk
shear around 40 kts, good moisture returns and a shortwave
trough providing lift, the one question for strong to severe
storms continues to be the presence of any instability.
Instability or the lack of it will be a fact in if storms roll
through the entire area or are on a dying trend as they push
east. Timing is still a bit uncertain on when storms are
expected to develop in the Dakotas and Minnesota. The further
west they develop then the later into the morning these storms
will move through. Meso models like the ARW and FV3 look to have
an early arrival time around 7 AM while the HRRR and NAM nest
delay storms a couple hours until around 10 AM. This difference
in timing and strength will then impact storms later in the
afternoon/evening with a second shortwave trough.

The second round of storms still has many questions yet to
answer in how this plays out. Similar to a game of cards, we
need to see how the first hand is dealt. No major changes yet
here for the forecast in the short term. Hoping the 00Z
guidance will shed some more light on the situation.

Patterson

&&

.SHORT TERM...
Issued 1229 PM CDT Sat Aug 8 2026

Tonight and Monday night:

A very unsettled pattern arrives late tonight as high pressure
pushes out ahead of an approaching low from the west. This
system will carry some punch with strong WAA in the low to mid
levels and a fairly substantial LLJ and a decent shortwave.
Given some sun ahead of storm development we should see at least
modest instability just ahead of the impending precip, and CAMs
backup the idea that some storm development should be expected
with the best chances further south of I-94 with the better
instability. How long storms persist is in question further
north given less instability but this part of the system should
be fairly progressive with storm activity pushing out by the
late morning to early afternoon. Cannot rule out severe storms
with this either given deep layer shear increasing to 50-60kts.
Altogether there is quiet a bit of uncertainty with morning
convection as the shear may lag behind the convection a bit
which would nix severe risk for the most part in addition to the
uncertainty with instability and the likelihood that storms
would most likely be elevated.

There may be a brief quiet spell in the early to mid afternoon
for a period of recovery before additional ripples in the upper
levels and the continued LLJ and the front all playing a role. A
secondary firing of convection appears likely for somewhere but
exactly where that occurs is still in question. Trends in models
have definitely shifted things a tad south more toward the WI-IL
border but this will be something to monitor as it will determine
how impactful this will be. Where these storms fire will
present an escalating heavy rain and flash flooding risk given
PWATs around 2 inches, west to east propagation and variable
corfidi vectors which is indicative of training convection with
back building. Some storms may become severe as well given
plenty of instability with deep layer shear around 40-50kts,
but the best chances will be on the south side of wherever
storms set up given the better continuous inflow.

CAMs are a bit all over the place with this convection with
uncertainty on where this sets up and for how long, but these
same models are also suggestive of things clearing out late
Sunday night. Into Monday uncertainty grows further but trends
have suggested that the front will sag further south perhaps
taking southern WI out of the primary risks for precipitation
and storms. There remains a chance that the front remains over
southern WI instead of pushing south which would keep the door
open for severe and flooding concerns so we will be closely
monitoring the progression of the front on Sunday into Monday.

Kuroski

&&

.LONG TERM...
Issued 1229 PM CDT Sat Aug 8 2026

Tuesday through Saturday:

As we remain stuck in this pattern with low pressure over Hudson
Bay and high pressure over the southern U.S. with weak shortwaves
in between, the forecast for southern WI will continue to be
uncertain in terms of storm chances and timing. Right now, it
looks like the main 850mb frontal boundary will end up stationed
in northern IL rather than southern WI, but there is still room
for that boundary to wiggle northward at times. That frontal
boundary will be the focus for storm generation from Tuesday
through Thursday morning.

So Monday night/Tuesday morning storms will once again depend on
the Monday storm movement and where the outflow and effective
front land. It will also depend on where the low level jet
develops Mon nt (and the position of the nose of the LLJ). It will
also depend on if there is a shortwave tracking across that
location at the same time in order to help initiate more organized
convection. Therefore, we have highest chances (55-65%) for storms in
the southern tier of counties Tuesday morning and lower chances
(30-45%) in the afternoon. The afternoon scenario would be for
additional storms firing along the stalled outflow boundary
(again, depends on where the morning convection takes it). Wednesday
storm chances are even less certain, but trending downward.

For Thursday through the next weekend, the GFS and ECMWF ensembles
are showing a 500mb height anomoly over the Great Lakes (an upper
trough) which could cause a round or two of storms in southern WI
with the associated frontal passage. That frontal passage could
move through southern WI as early as Wednesday night or as late as
Thursday night. While the ECWMF ensemble suggests that the upper
low is progressive and quickly brings ridging into southern WI by
Saturday 8/15, the GFS Ensemble forecasts that this upper low will
stall over the Northeast through at least the first half of the
following week.

Cronce

&&

.AVIATION...
Issued 730 PM CDT Sat Aug 8 2026

VFR conditions are expected into early this morning then
conditions are expected to fall to MVFR to IFR. The mostly clear
skies this evening will remain into the early morning hours.
Rain and thunderstorms are expected to move through southern
Wisconsin during the morning hours and exit to the east late
morning/early afternoon. Heavy rain will be possible with any
storms which could drop visibilities to 1-3 SM or less for a
brief period of time. A few stronger storms may be possible
with wind being the primary concern. Can't rule out any small
hail. Ceilings are expected to be around 2-6 kft with the
storms. Additional storms will be possible in the late
afternoon/evening. There is uncertainty in the strength of the
second round of storms due to how long the morning round lasts.
If the morning round is weak and fast then there will be a
chance for strong to severe storms again in the evening. Heavy
rain, flooding and strong winds will be the main concerns.
Visibilities and ceilings expectations will be very similar to
the morning round. VFR conditions may briefing return after the
rain ends, but low stratus and patchy fog may develop late
Sunday night. Any fog that develops late Sunday into early
Monday could drop visibilites to 2-4 SM.

Light west to southwest winds this evening will stay
southwesterly and increase slightly during the early morning
hours. Breezy south winds will move in during the late
morning/afternoon outside of any rain/storms. Light and variable
winds are expected Sunday night into Monday morning.

Patterson

&&

.MARINE...
Issued 1229 PM CDT Sat Aug 8 2026

Low pressure of 29.5 inches over the Hudson Bay has carried its
cold front across the lake with west to northwest winds behind the
front this morning that will quickly return to southerly by this
evening ahead of the next approaching low pressure system. An
unsettled weather pattern will set up over the Upper Great Lakes
next week where weak waves of low pressure will cross the region
and produce rounds of thunderstorms at times.

Kuroski

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...None.
&&

$$

Visit us at weather.gov/milwaukee

Follow us on Facebook, X, and YouTube at:
www.facebook.com/NWSMilwaukee
www.x.com/NWSMilwaukee
www.youtube.com/NWSMilwaukee