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 Monday afternoon through Tuesday. Additional heat headlines may be needed for the second half of the week, but some uncertainty remains.

- Continued chances for showers and storms this evening, en into specially for east-central WI. Then additional daily storm chances Tuesday evening through Friday with this hot and humid pattern.

- High swim risk conditions for Ozaukee and Sheboygan county beaches while moderate swim risk for Milwaukee and Racine county beaches for Monday.

SHORT TERM

Issued 245 PM CDT Sun Jun 28 2026

Tonight through Tuesday night:

Remnant MCS is trekking across southern WI this afternoon following along the band of 700 mb frontogenesis and mid-level shortwave trough. While it is mainly bringing light to moderate rainfall with the stronger activity following the better SBCAPE gradient and warm front into northern IL, there has been enough elevated instability over southern WI for a few flashes of lightning and rumbles of thunder to occur within the stratiform region of this complex. Cannot completely rule out seeing this line reinvigorate some as it moves toward the lake as this area has had some time to warm up and build up a bit more instability (MUCAPE of around 500mb based on 18z RAP) and paired with the synoptic forcing mechanisms and localized MCV forcing. Will be monitoring radar trends and see if this materializes, if so could see some gusty winds. in addition to the lightning threat. Otherwise, expect this shower and occasional thunder activity to work east through the remainder of the afternoon and pushing out by the evening.

Then will be another chance for showers and thunderstorms this evening mainly across the central and east-central WI north of I-94 as the warm front lifts northward and low-level WAA joins the remnant 700 mb frontogenesis band and nose of 30-45kt LLJ. Much of this activity looks widely scattered with light to moderate rainfall. This activity should progress northward and exit our CWA around daybreak, but lingering cloud cover may persist through the start of the morning.

Otherwise, the upper-level ridge axis continues to build over the region into Monday with overnight lows tonight starting of in the upper 60s to lower 70s. Then continue to see the hot and humid conditions settling in over the Midwest. While any lingering cloud cover may slow the morning temps, expect things to clear up mid-late morning with temps quickly climbing into the 80s and 90s by the afternoon. Pair with the dewpoints in the lower 70s, heat indices of +100F is expected across much of the area and even expecting to see +105F heat indices. Areas right along and just inland of Lake Michigan will see the coolest conditions, but still hazardous heat. Thus have upgraded and issued an Extreme Heat Warning for all of southern WI Monday afternoon.

Have elected to continue the Extreme Heat Warning Monday evening/night as there is not expected to be much relief from the heat with overnight lows expected in the mid to upper 70s and even warmer heat indices. Also have extended the Warning into Tuesday as southern will see another hot and humid day for Tuesday as the blocking high over southeastern CONUS keeps the upper-level ridge over the Upper Midwest. Looking at afternoon temps in the mid 90s and +100F heat indices. while cannot rule out few stray showers and storms to develop in this muggy environment, there is not much in the way of forcing to trigger this activity until later Tuesday.

Overall, the week will start off with a prolonged period of heat paired with humid conditions resulting in heat related issues and concerns. Stay weather aware and keep cool and hydrated.

Lastly increasing southerly onshore flow developing overnight into Monday will build waves along southeastern WI beaches resulting in elevated swim risk conditions. Highest waves of 4-6 feet and conditions favoring dangerous currents will be for Sheboygan and Ozaukee county beaches Monday. Still looking at moderate swim risk conditions for beaches south along Milwaukee and Racine county beaches.

Wagner

LONG TERM

Issued 245 PM CDT Sun Jun 28 2026

Wednesday through Sunday:

Midweek onward is expecting to see similar set up with the upper- level ridge situated over the Great Lakes through the end of the week. Thus, will continue to see hot and humid conditions with daytime heat indices in the upper 90s to around/above 100F. Additional heat headlines are possible for the second half of the week. However, the biggest difference from the start of the week through the end of the week, is the increased chances for daily showers and thunderstorms. As noted yesterday models have the ridge axis slightly further east than earlier model runs, placing the southern WI under the peripherals and even within the upper-level jet. Any shower and storm activity, depending on timing/development as well as remnant cloud cover may influence temps as well as heat indices each day Wednesday through Friday. Thus, not as certain on the higher heat indices at this point and additional heat headlines (warning/advisory) decision will be taken day-by-day.

Regardless of the heat headlines/thresholds and storm chances, still looking at periods of daytime heat indices in at least the 90s and above each day along with warm nightly lows for the end of the week. Thus, prolonged nature of the pattern due to the blocking high will likely be case for continued heat related issues/concern across southern WI, especially for vulnerable populations without easy access to stay cool and those spending extended periods outside.

There are some hints in the long-range models of the ridge breaking down a bit toward the holiday weekend with a series of disturbances tracking across the region, but still plenty of time for things to evolve and change given the midweek pattern.

Wagner

AVIATION

Issued 245 PM CDT Sun Jun 28 2026

Line of light to moderate showers and a few rumbles of thunder (mainly along and south of I-94) continue through the afternoon and exits by the early evening. Main concern would be brief gusty winds and minor reduction of visibility. Then there will be another chance of showers and storms for east-central WI later this evening and overnight as the warm front lifts north and may see a period of lower ceiling to around or even below MVFR with the overnight activity. Otherwise, the southeasterly winds this afternoon and evening will gradually turn more southerly into Monday as heat and humid conditions settle across the region. Accompanying this pattern shift will be gusty winds late Monday morning through the afternoon and gusts of 25kt possible. VFR conditions are mainly expected mid Monday morning through the evening.

Wagner

MARINE

Issued 245 PM CDT Sun Jun 28 2026

Low pressure over the Plains continues to deepen and shift winds more southerly across Lake Michigan tonight into Monday. Stronger winds and builds waves will result in small craft conditions tonight for areas north of Port washington, while conditions develops Monday afternoon for nearshore south of Port Washington to Winthrop Harbor. Breezy southerly winds will persist through midweek as the blocking high over the southeast US brings hot and humid conditions to the region. Additionally will see daily thunderstorm chances return for the end of he week into the weekend.

Wagner

MKX WATCHES/WARNINGS/ADVISORIES

WI...Beach Hazards Statement...WIZ052-WIZ060...4 AM Monday to 10 PM Monday.

LM...Small Craft Advisory...LMZ643...4 AM Monday to 10 PM Monday.

Small Craft Advisory...LMZ644-LMZ645-LMZ646...noon Monday to 10 PM Monday.