Sun Prairie, Wisconsin 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

888
FXUS63 KMKX 291952
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
252 PM CDT Mon Jun 29 2026

.KEY MESSAGES...

- Expecting hot and humid conditions through much of the week
  leading to hazardous/dangerous heat related concerns due to a
  combination of daytime heat indices in the 90s to above 100F,
  the first stretch of heat this summer spanning multiple days
  beginning Monday, and not much overnight relief with overnight
  lows only in the 70s each night.

- Extreme Heat Warning in effect for all of southern WI tonight
  through Wednesday. Additional heat headlines may be needed for
  the second half of the week, but some uncertainty remains.

- Could see some showers/storms overnight lingering into
  Tuesday. Then additional daily thunderstorm chances Wednesday
  through the end of the week as the hot and humid pattern
  continues.

- High swim risk conditions for Ozaukee and Sheboygan County
  beaches until this evening, with moderate swim risk
  conditions for Milwaukee and Racine Counties.

&&

.SHORT TERM...
Issued 247 PM CDT Mon Jun 29 2026

Tonight through Wednesday:

Hot and humid is the name of the game through the first half of
the week as the upper-level ridge is set up over the Midwest
with a blocking high over the southeastern CONUS. Extreme Heat
Warning has been extended through at least Wednesday at this
point given the prolonged nature of daytime heat indices
expected to rise above 100F each afternoon and overnight heat
indices in the upper 70s. Areas immediately along the lakeshore
of Lake Michigan along with any onshore wind component may be
cooler by a few degrees, but still will see impacts from the
heat/humidity regardless. Even with cloud cover lingering this
afternoon, we are seeing heat indices above 100F and even higher
with pockets of clearing and dewpoints running warmer than
models suggested. Thus, have higher confidence of seeing similar
heat indices Tuesday into Wednesday.

While the hot and humid conditions are the main story, these
conditions are also favorable ingredients for thunderstorm
activity. It will not take much to trigger a storm or two to
develop with these conditions, however, it needs a trigger to
initiate development and tap into the moisture and instability
settled across the region. Each CAM has a different solution and
potential trigger for any activity overnight and Tuesday, but
its tough to pinpoint if and what type of trigger would be. The
12z NAM nest, and ARW have convection upstream be the focus for
some showers and storms to develop overnight and track across
and north of the area, with the RRFS being more aggressive with
deeper develop more into Tuesday off of something coming off
the storms that may develop in the Plains tonight (which seems
most unlikely scenario, but not impossible). Meanwhile the HRRR
and NSSL keep us dry and any convection to the north. So while
potential is there and cannot rule out seeing a few storms
trigger along remnant boundaries or a gravity wave from upstream
storms, the influence and subsidence from the ridge may
ultimately limit any of this activity Tuesday, but Wednesday
might have better potential as the ridge axis shift further east
and upper- level jet influence creeps toward our western CWA.
Nevertheless, it does bear watching the mesoscale trends and how
the environment evolves overnight through Tuesday.

Wagner

&&

.LONG TERM...
Issued 247 PM CDT Mon Jun 29 2026

Wednesday night through Monday:

Hot and humid conditions persist into the second half of the
week with additional heat headlines possible given persisting
+100F heat indices. However, pattern remains more uncertain as
the ridge axis slide further east and potential for daily shower
and thunderstorm chances increase. Models hint at a bit more
upper-level support in the form of mid-level vorticity lobes
overrunning the ridge along with LLJ and upper-level jet
moving more in place. Thus, could see the extreme heat pattern
break down a bit into the holiday weekend. Nevertheless, still
looking at above normal temps and muggy conditions accompanying
the daily storm chances for the end of the week.

Wagner

&&

.AVIATION...
Issued 247 PM CDT Mon Jun 29 2026

MVFR ceilings have scattered out this afternoon with gusty
south- southwesterly winds. Winds doe look to ease this evening
and tonight before picking back up for Tuesday. Otherwise,
mainly expecting VFR conditions to prevail this evening into
Tuesday, but give the humid pattern could not rule out see some
visibility reductions along the lakeshore along with some lower
ceilings at times through the period.

Wagner

&&

.MARINE...
Issued 247 PM CDT Mon Jun 29 2026

Southerly winds will continue this afternoon into the evening
but gradually shift southwesterly. Given the humid airmass and
cooler airmass will be potential for fog over Lake at times,
particularly the northwestern quadrant of the Lake along
northeastern WI to mid lake. Otherwise, with low pressure
developing over the Plains and high pressure lingering over the
Southeast US, expect breezy conditions to continue through much
of the week. The hot and humid airmass settled over the region
will also bring daily thunderstorms chances to portions of the
lake through the end of the week.

Wagner

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Beach Hazards Statement...WIZ052-WIZ060 until 10 PM Monday.

LM...Dense Fog Advisory...LMZ563-LMZ565-LMZ567-LMZ669 until 7 AM
     Tuesday.

     Dense Fog Advisory...LMZ643...10 PM Monday to 7 AM Tuesday.

     Small Craft Advisory...LMZ643-LMZ644-LMZ645-LMZ646 until 10 PM
     Monday.

&&

$$

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