NWS-Milwaukee/Sullivan Forecast Discussion
FXUS63 KMKX 171916
AFDMKX
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
216 PM CDT Fri Jul 17 2026
.KEY MESSAGES...
- Warm and humid conditions continue into Saturday with heat
indices in the 90s.
- The Air Quality Advisory issued by the Wisconsin Department of
Natural Resources remains in effect until 6pm for lakeshore
and lakeshore adjacent counties. Wildfire smoke is expected to
continue contributing to lower visibilities and
unhealthy/hazardous air quality.
- Chance of thunderstorms into Saturday and again later Monday.
Severe Weather may be possible Monday.
- High Swim Risk conditions may occur at all southern WI beaches
Saturday night.
&&
.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 hintining 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 208 PM CDT Fri Jul 17 2026
Smoke is quickly clearing from southern Wisconsin, allowing for
VFR conditions over most of the area. Scattered showers and
storms are popping up amid the afternoon heat and are expected
to continue until the sunsets this evening. These are slow
moving and very hit or miss but may produce heavy downpours and
lightning. Cloud bases will generally range from 3500 to 5000
feet with the shower and thunderstorm activity. Skies clear
tonight with low smoke concentrations expected. A cold front is
then expected to move through Saturday morning, with some more
potential for thunderstorms along the front as it moves south
through the area. Winds are expected to be light to moderate and
southwesterly through the rest of the afternoon and into
tonight. Then, northerly winds and higher smoke concentrations are
expected following the cold frontal passage on Saturday.
CMiller
&&
.MARINE...
Issued 208 PM CDT Fri Jul 17 2026
Southerly winds continue through tonight as low pressure moves
east across Lake Superior. This low pressure system is expected
to drag a cold front down the lake on Saturday with the front
pass pushing south of the lake by Saturday night. Breezy
southerly winds are expected ahead of the front, with the
strongest winds expected over the northern end of Lake MI. Winds
then quickly veer northwesterly and northerly following the
frontal passage on Saturday. In the cold advection regime behind
the front, north wind gusts may approach 30 knots, particularly
over the southern half of the lake.
Winds then quickly taper Saturday night as high pressure moves
over the northern Great Lakes. Northeast to light and variable
winds are then expected through Sunday into Sunday night.
CMiller
&&
.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...None.
&&
$$
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