NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 280140
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
840 PM CDT Sat Jun 27 2026

.KEY MESSAGES...

- Expecting hot and humid conditions through much of next week
  leading to dangerous heat index values and associated risks,
  such as heat exhaustion and heat stroke. Heat headlines are
  expected at times.

- Chance for showers and storms for late Sunday afternoon into
  the evening with additional daily chances Tuesday through
  Friday.



&&

.UPDATE...
Issued 840 PM CDT Sat Jun 27 2026

Light ely surface winds will continue tnt as high pressure remains
over the nrn Great Lakes and srn Ontario. A weak 925-850 mb sely
flow tnt will begin the warm, moist advection aloft and may
bring north some scattered to sometimes broken stratus late this
evening into the overnight. Some of these clouds could linger
through Sun AM before mostly dissipating.

For Sun afternoon a decaying MCS is expected to mostly dissipate
as it moves into sw and south central WI. 850-700 mb warm, moist
advection will support the MCS across srn MN in the morning,
but it begins to run into very warm and dry mid level air that
will already be in place across srn WI by late Sun AM into the
afternoon. Only 20 percent chances for showers and storms is
forecast west and north of the MKE metro area.

The low to mid level warm advection will increase late Sun
afternoon through Mon AM as the high amplitude upper ridge
builds into the Great Lakes. The surface warm frontal passage is
expected Mon AM. Only 20-30 percent chances of showers and
storms are forecast Sun nt toward central WI, as the very warm
and dry 700 mb air will attempt to inhibit elevated convection.
A hot, humid and capped airmass will finally arrive by Mon
afternoon with high temps in the lower to middle 90s and
dewpoints in the lower to middle 70s. This will yield heat index
values of 100-105F. A Heat Advisory will likely be needed with
additional heat headlines through the week.

Gehring

&&

.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 840 PM CDT Sat Jun 27 2026

VFR conditions will prevail tnt-Sun evening. Local MVFR Cigs may
occur at times late tnt into the Sun AM daylight hours as a
moist sely flow begins at 925-850 mb. Low stratus (600-1500
ft.) are then expected to develop over much of srn WI late Sun
evening into the overnight as the warm front approaches.

Gehring

&&

.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.
&&

$$

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