NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 180246
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
946 PM CDT Fri Jul 17 2026

.KEY MESSAGES...

- Very warm and humid conditions continue into Saturday with
  heat indices in the lower to middle 90s along and south of
  Interstate 94.

- Wildfire smoke is expected to return Saturday night and Sunday
  with unhealthy air and reduced visibility expected.

- Slight chance to chances of thunderstorms late tonight into
  early Saturday afternoon.

- High Swim Risk conditions may occur at all southern WI beaches
  Saturday night.

- Numerous thunderstorms, possibly severe, are forecast Monday
  and Monday night.


&&

.UPDATE...
Issued 946 PM CDT Fri Jul 17 2026

Introduced slight chance PoPs tnt as a wly 850 mb jet of 30 kts
and thermal ridge shifts swd into the area just ahead of the
approaching cold front. PWATs will increase to 1.6-1.9 inches
during the overnight with elevated CAPE of 2000 J/KG expected.
The CIN will be weak but so is the forcing. The cold front will
track from nw-se across the area from 10-16Z with a continued
possibility for development as it moves toward the IL border.
Sfc based convection may become possible toward the border by
late morning, but much of the expected storm development will be
in nrn IL in the afternoon.

Nly winds and weak cold advection will then settle over srn WI
for the afternoon including a lake breeze boosted by the front.
High temps in the middle to upper 80s will likely be reached by
noon over far ern WI before cooler lake air moves inland. Heat
index values on Sat will range from the upper 80s north of I-94
to the lower 90s south. High pressure will then settle over the
nrn Great Lakes and nrn WI Sat nt, then moving to lower MI and
Lake Huron on Sun. Cooler low temps in the lower to middle 60s
is forecast Sat nt with highs Sun in the upper 70s to lower 80s.
The high temp forecast for Sun is accounting for fairly
widespread smoke that will arrive Sat nt and continue through
Sun.

Gehring

&&

.SHORT TERM...
Issued 205 PM CDT Fri Jul 17 2026

Tonight through Saturday night:

Smoke is expected to clear from southwest to northeast over land
areas of southern Wisconsin through the rest of the afternoon.
HRRR model guidance suggests that some smoke may get trapped in
the marine layer immediately near the Lake Michigan shoreline
late this afternoon, but remaining smoke should clear from south
to north over the lake into the evening hours. Wherever the sky
clears from the smoke will be in a better position to receive
solar insulation, and some isolated pop up showers and maybe a
rumble of thunder or two may occur, though CAPE profiles are
skinny and low levels will be dry so any activity will struggle.

There will be a brief reprieve from the smoke tonight into the
morning hours on Saturday before a cold front moves in from the
north during the late morning. Some CAMs, most notably the HRRR,
struggle to convect Saturday morning ahead of the cold front
despite having an uncapped and unstable Cape profile and little
signs of subsidence in the soundings. If heating is sufficient
enough to hit the convective temperature ahead of the cold front
there may be a few storms along the I-94 corridor and southward
during the late morning into the early afternoon before the
front pushes south into Illinois. Soundings support the presence
of some hail and gusty winds cant be ruled out with any dying
thunderstorms. For now, have decided to include chance PoPs
around 30% for the storm threat tomorrow morning into the early
afternoon. Higher smoke concentrations are anticipated in the
wake of the cold front tomorrow afternoon into tomorrow evening
and AQI is expected to return to the unhealthy category judging
by EPA forecasts and morning runs of the HRRR smoke model.

Overnight lows tonight are expected to be in the 70s with highs
in the upper 80s on Saturday. Dew points will remain muggy until
the cold front pushes through Saturday afternoon.

CMiller

&&

.LONG TERM...
Issued 205 PM CDT Fri Jul 17 2026

Sunday through Friday:

Saturday night into Sunday, high pressure is expected to build
into the upper Great Lakes region. As a result Sunday should
remain quiet with drier dew points but warm 925mb temps should
still keep highs in the mid 80s. Sunday night the high pressure
system is expected to exit east towards the lower Great Lakes
and southerly flow will return from midnight Monday onward.
Southerly flow will allow for surface dew points to moisten and
warm advection aloft is likely to trigger a round of
thunderstorms over central and northern Wisconsin during the
morning hours on Monday. From here model solutions diverge with
the 12z run of the GFS favoring the potential for the morning
storms over northern Wisconsin to intensify into a southeastward
moving MCS Monday afternoon, while the ECMWF favors 2 distinct
rounds, one in the morning and one in the evening. Whatever the
solution, model soundings suggest a volatile environment with
4000 to 5000 joules per kilogram of surface based Cape,
effective shear eclipsing 35 knots, and great diffluence aloft
from an impinging trough at 500mb. Given the potential for the
volatile thermodynamics, the potential for a forward propagating
MCS, and 0 to 3km shear > 30 knots hinting toward QLCS
potential, all severe weather hazards look possible. The Storm
Prediction Center has outlooked all of Wisconsin under a 15%
highlighting the severe weather risk. Forecast model trends will
be monitored through the weekend regarding this severe weather
threat.

Afterward, generally mild and dry conditions take hold as a
Canadian high pressure moves southeast over the Great Lakes
region. There are some hints we get back into a more active
pattern toward the end of the work week.

CMiller

&&

.AVIATION...
Issued 946 PM CDT Fri Jul 17 2026

VFR conditions tnt-Sat but with low chances for showers and
thunderstorms early Sat AM into early Sat PM. Sct-bkn040-060
expected during this period. Areas to possibly widespread smoke
will then move into srn WI late Sat afternoon through the
evening and continue well into Sunday. Vsbys may fall to 1-2SM
with the smoke with areas of Cigs of 2-3kft.

Gehring

&&

.MARINE...
Issued 946 PM CDT Fri Jul 17 2026

Areas of smoke will continue over the north half of the lake
tonight. Otherwise breezy southwest to west winds will develop
ahead of a cold front. The low pressure area around 29.7 inches
will track from just north of Lake Superior tonight across
southern Quebec Saturday afternoon and deepen to 29.4 inches. Its
trailing cold front will track from northern Lake Michigan
Saturday morning to far southern Lake Michigan by early afternoon.
Smoke will return to Lake Michigan behind the cold front and may
become dense once again. Breezy northerly winds are forecast
behind the cold front and will linger into Saturday evening.

Winds then quickly taper Saturday night, as high pressure around
30.1 inches moves over the northern Great Lakes. Northeast to
light and variable winds are then expected through Sunday into
Sunday night. Gusty south to southwest winds may then develop
Monday into Monday night, with gusty west to northwest winds
possible into the middle of next week.

Gehring

&&

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

$$

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