NWS-Milwaukee/Sullivan Forecast Discussion
FXUS63 KMKX 271940
AFDMKX
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
240 PM CDT Sat Jun 27 2026
.KEY MESSAGES...
- Expecting hot and humid conditions through much of next week
leading to hazardous/dangerous heat related concerns due to a
combination of daytime heat indices in the 90s to above 100F
at times, the first stretch of heat spanning multiple days of
the summer beginning Monday, and not much overnight relief
with overnight lows only in the 70s each night.
- Any heat headlines for southern WI for the start of the week
will be taken day-by-day as factors such as daily storm
chances and eastern shift in the upper-level pattern all will
play a role in meeting heat thresholds.
- Chance for showers and storms for late Sunday afternoon into
the evening with additional daily chances Tuesday through
Friday.
&&
.SHORT TERM...
Issued 232 PM CDT Sat Jun 27 2026
Tonight through Sunday night:
High pressure over the Upper Great Lakes this afternoon will
continue to slide eastward overnight with east winds turning
more southeasterly into Sunday. Tonight expect one more night of
lows in the upper 50s to lower 60s. Will begin see the upper-
level ridge axis begin to build to our west over the Upper
Mississippi River Valley. As a result, expect warmer temps and
higher dewpoints begin to advect into southern WI through the
day Sunday. Southeasterly flow off of cooler Lake Michigan will
still keep things milder along the lakeshore areas with highs in
the mid to upper 70s, while areas inland and west of the Kettle
Moraine look to warm into the lower to mid 80s by the
afternoon.
Accompanying the start of the warm up will be a potential for a
few showers and storms to develop in the afternoon and evening.
Overall, much of the 12z CAMs hint at a decaying MCV from
upstream convection to track across the Upper Midwest later in
the morning through the afternoon and bring only some light and
scattered shower to southern WI. There is enough of a signal
with this activity to warrant lower PoP and thunderstorm chances
(15-40%). However, will need to keep an eye on how things
develop upstream and evolve overnight as cannot rule out that we
could see a few more developed and stronger storms develop. The
12z models continue to hint that this decaying system will be
moving into an environment with synoptic forcing as a mid- level
ripple of vorticity treks across the area while low-level WAA
builds northward along with a swath of 700 mb frontogenesis
swings through. Pair with the increasing moisture and building
instability approaching 750-1200 J/kg of SBCAPE toward
southwestern CWA.
While there are synoptic ingredients favoring development,
there remains a few factors that limit much of the development.
The first being the strong capping inversion as seen on the
model soundings where the strongest instability is progged to
set up. The other factor will be the alignment of these
ingredients as they may stay offset and not come together to
actually develop much. While the aforementioned limiting factors
paired with the CAMs is the most likely scenario, cannot
completely rule out the MCV influence to spur additional
development through the afternoon, especially if we see the
upstream activity develop further south as hinted by the 12z
NAMnest as well as the Canadian.
Wagner
&&
.LONG TERM...
Issued 232 PM CDT Sat Jun 27 2026
Monday through Saturday:
The continued focus for the extended period continues to be the
hot and humid pattern setting up over the region through the
end of the week. Still seeing trends of daytime temps in the 90s
with dewpoints in the 70s resulting in heat indices of 100F or
more at times Monday through at least Wednesday. Nightly lows
will also be a concern as models and ensembles prog 70s for much
of the week. The combo of these conditions paired with the
first hotter stretch of the season will likely lead heat related
issues and concerns.
While the signal for this heat continues, there remains caveats
with this pattern still being a few days out. First of these
will be the upper-level ridge placement. Still expecting the
upper-level heights to continue to build over the Upper Midwest
for the start of the week, however the 00z-12z mid-range global
models and ensembles have been trending the axis of this ridge a
bit further east compared to previous days models. As a result,
southern WI could become placed more along the peripherals or
even within the southwesterly upper- level jet. Thus
contributing to increased potential for impulses of upper-level
vorticity maxes to over run the top of ridge and pair with the
warm and humid conditions to bring daily shower/storm chances to
area as hinted by the 12z GFS, ECMWF, and CMC model runs. Given
the eastern shift in upper-level pattern and increased
potential for daily shower/storm chances Tuesday-Friday, may
ultimately influence temps/heat indices each day, especially
for the later half of the week.
Overall, will be best to handle things day-by-day for next week
as influence from previous day's activity will play a role as
well, especially with heat headlines. Monday still looks
favorable for over 100F heat indices as the ridge begins to
build into the region and likely see the Heat Advisory threshold
be met, but at this time looks to stay below 105F threshold for
a warning. Tuesday continues to trend as the hottest day of the
week with heat indices teetering between advisory and warning
thresholds at this time, but this is when models suggest the
eastward shift in the upper-level jet and ridge axis come more
into play. These influences will then continue through the
middle of the week with uncertainty growing each day Wednesday
onward.
Regardless of the heat headlines/thresholds and storm chances,
still looking at periods of daytime heat indices in the 90s and
above each day along with warm nightly lows for multiple days
through next week. Even if the not as hot side of the forecast
pans out, these factors will be enough to create hazardous heat
related issues across southern WI, especially for vulnerable
populations without easy access to stay cool and those spending
extended periods outside.
Wagner
&&
.AVIATION...
Issued 232 PM CDT Sat Jun 27 2026
VFR conditions prevail through the evening and into Sunday as
high pressure over the Upper Great Lakes slides farther east.
Mainly looking at a wind forecast with breezy easterly winds
this afternoon ease and shifting more southeasterly into Sunday.
Will continue to monitor for the potential shower and storm
development Sunday afternoon, but not enough confidence to add
into the TAFs at this time.
Wagner
&&
.MARINE...
Issued 232 PM CDT Sat Jun 27 2026
Lighter winds over the lake continue as high pressure over the
Upper Great Lakes gradually slides east through the day Sunday.
Will see winds begin to pick up as low pressure develops and
deepens over the Plains. Will see more southerly winds over Lake
Michigan for the start of week with occasional gusts of 25-30
knots as the hot pattern setups across the region through
midweek. With these gusty winds, small craft conditions for
southeastern and east-central WI nearshore zones will be
possible overnight Sunday into Monday.
Wagner
&&
.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