textproduct: Milwaukee/Sullivan

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.