NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 182036
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
336 PM CDT Fri Jul 18 2025

.KEY MESSAGES...

- An area of showers and thunderstorms will likely (50 to 70
  percent chance) roll into south central WI early Saturday
  morning and exit southeast WI by midday. Gusty winds are
  possible with stronger storms.

- Additional showers and thunderstorms are possible Saturday
  afternoon along a cold front. Storms may produce damaging
  winds and hail.

- Chances for storms develop on and off early through late next
  week, but timing and intensity remains uncertain at this time.

- Heat builds back into the region with highs in the upper 80s
  to lower 90s Tuesday into the end of the week.

&&

.SHORT TERM...
Issued 336 PM CDT Fri Jul 18 2025

Tonight through Saturday night:

Light winds and lows in the mid to upper 60s through midnight, as
high pressure exits to the east and winds kick southeasterly and
bring a return to warm, moist conditions.

Exiting 200 mb jet will continue to produce showers and
potentially thunderstorms across northern Minnesota and northern
Wisconsin into tonight. Warm frontogenesis developing across the
same region will bring additional lift and allow storms to
progress southeastward through the overnight hours as the front
sags southward. A second area of storms will develop early tonight across
northern Nebraska at the apex of the 850 mb LLJ, following bulk
shear vectors east-southeastward through Iowa overnight.
Placement and extent of these features remain uncertain, and
likely will continue to be uncertain until they complete their
development tonight.

Two main solutions arise, with the first, more intense scenario
indicating that plenty of moisture and elevated instability
indicated by MUCAPE of 1000 to 1500 J/kg will only require a
trigger to fire off storms across southern Wisconsin, allowing the
two storm systems to connect through southern Wisconsin due to
phasing of their respective shortwaves. this would allow for
lightning and locally heavy rain, with potential south of I-94 to
produce strong to severe storms as the southern MCS taps into
better instability along the Wisconsin/Illinois border and
intensifies into the Saturday morning timeframe. The second, less
intense scenario depicts only isolated to scattered storms across
southern Wisconsin with each MCS remaining separated throughout
the overnight hours into Saturday morning. Regardless of solution,
morning convection ends by noon at the latest.

Going into Saturday afternoon, a cold front from a weak low
pressure system traversing northern Wisconsin into Michigan will
drag across southern Wisconsin. Due to the uncertainties lingering
for overnight convection, uncertainties continue into Saturday
afternoon. If phasing occurs and more widespread convection
develops across southern Wisconsin Saturday morning, overcast
skies will likely linger and prevent diurnal heating from
destabilizing the atmosphere. This would allow for weak, pulse-
type thunderstorms along the front. However, if no phasing occurs
overnight and conditions remain relatively dry, clearing skies and
a redevelopment of convection is possible. This would lead to
stronger storms along the front, capable of producing gusty winds
and small hail. All storms will exit into Lake Michigan going into
late Saturday evening.

CAMs depict potential for thunderstorm development along the
Wisconsin/Illinois border once again Sunday night along the now-
stationary front, bringing slight chances for precipitation across
far southern Wisconsin (20-30 percent). Lows in the lower 60s.

MH

&&

.LONG TERM...
Issued 336 PM CDT Fri Jul 18 2025

Sunday through Friday:

Stationary front remains just south of the Wisconsin border
through Sunday and into Monday as high pressure settles into the
Great Lakes region once again. On and off chances for showers and
storms are expected across far southern Wisconsin, but chances
remain low (15-30 percent). Low pressure develops and pushes
eastward into the Upper Midwest on Tuesday, bringing stiff
southerly winds and heat back to southern Wisconsin through the
day (highs in the mid to upper 80s). Warm frontal feature will
lift into the region Tuesday night, with potential for storms
along it (30-50 percent chance). Heat continues into Wednesday,
with highs in the upper 80s to lower 90s within the warm sector.
Timing is in question for the low's progression eastward, but best
chances for thunderstorms in the evening to overnight (40-50
percent chance).

Ridging continues to build across the southern U.S. Wednesday
through Friday, putting southern Wisconsin firmly into the ridge
riding MCS setup. Therefore, NBM PoPs of 20-40 percent linger
through the rest of the week. Still, expecting future refinements
to the forecast to nail down specific timeframes of interest with
future modeling. Regardless of exact timing of storms, expect heat
and humidity to continue into Friday.

MH

&&

.AVIATION...
Issued 336 PM CDT Fri Jul 18 2025

Scattered deck around 2500 ft near Lake Michigan will slowly
dissipate this evening, while scattered deck around 3500 to 4500
ft does the same inland. Southeasterly winds are expected to
dominate, but will remain weak and sometimes variable through this
afternoon and evening. Late tonight into early Saturday morning, a
thunderstorm complex will develop across northern Wisconsin, and
an additional thunderstorm complex will develop across Iowa. A
line of scattered thunderstorms may develop across southern
Wisconsin during this time frame, bringing briefly gusty winds,
reduced visibilites, and MVFR cloud decks, especially to southern
terminals. Winds shift to southwesterly behind this activity. Storms
will exit to the southeast by noon on Saturday, with isolated
storms possible again along a cold front Saturday afternoon. More
scattered, stronger storms are possible Saturday afternoon if
Saturday morning convection does not develop. Winds shift to
become northwesterly behind the cold front.

MH

&&

.MARINE...
Issued 336 PM CDT Fri Jul 18 2025

High pressure over the Great Lakes region will slowly exit to the
east tonight as low pressure develops in the lee of the Colorado
Rockies. A warm front will develop across northern Wisconsin and
the Upper Peninsula overnight, bringing thunderstorms to the
northern half of the lake into the late overnight hours.
Additional thunderstorm development is expected across the
southern half into Saturday morning. Winds become southwesterly as
these storms end midday Saturday, then become northerly behind a
cold front Saturday afternoon. Isolated thunderstorms are possible
along this front. High pressure will settle back into the region
on Sunday, slowly departing into Monday and shifting winds to
easterly. A low pressure trough will cross the Upper Midwest on
Tuesday, bringing southeasterly winds.

MH

&&

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

$$

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