textproduct: Milwaukee/Sullivan

KEY MESSAGES

- Chance for showers and storms for late Sunday morning/afternoon.

- Prolonged period of hot and humid conditions expected for the start of next week through end of the week with potential for heat indices around to above 100F.

- Additional shower/storm chances accompanying the heatwave Tuesday through end of week

SHORT TERM

Issued 138 PM CDT Fri Jun 26 2026

Tonight through Saturday night:

Zonal upper-level flow and a weak low pressure tracking across central IL bringing the cloudy conditions this afternoon will continue to shift east this evening. Looking at lingering cloud cover to insulate the area and keep temps overnight a degree or two warmer than previous forecast with lows dipping low to mid 50s.

Then looking a upper-level ridge begins to build across the region for Saturday. Will begin to see warmer temps along with higher dewpoints (upper 50s to around 60F) advect into southern WI. However, easterly onshore flow on the backside of the departing weak low and north of a frontal boundary will ultimately prevent the warmer temps. Only looking at daytime highs in the mid to upper 70s for areas along and east of the Kettle Moraine while upper 70s to low 80s for areas west/further inland for Saturday. While expect less cloud cover for Saturday, cannot rule out a few more patches of mid to high level clouds fill in as suggested by 12z HREF, which could knock daytime temps down a few degrees. Otherwise, overnight lows are trending warmer than the previous night with upper 50s to low 60s.

Wagner

LONG TERM

Issued 138 PM CDT Fri Jun 26 2026

Sunday through Friday:

The upper-level ridge continues to build across Upper Mississippi River Valley and bringing the warmer and muggier conditions to southern WI. However, models continue to hint at a mid-level vorticity max overrunning the top of the building upper-level ridge and trekking across the region later Sunday morning. The tail end of the 12z CAMs are hinting at MCV type structure and this disturbance paired with the low-level WAA and increasing moisture looks to be enough for a scattered showers and storms chances (20-40%) across southern WI. Given the general timing of late morning/early afternoon of this feature, the NAM along with GFS and ECMWF are hinting at some increased deep-layer shear and building instability with MUCAPE creeping toward 750-1200 J/kg with this system. While, difficult to pinpoint if these features will line up pairing with the influence from the MCV, but it is not out of the realm of possibility to see a bit more widespread coverage in activity than latest models suggest and even a potential for a few stronger storms cannot be ruled out, especially a slightly later timing. Will monitor as CAMs come more into range.

Otherwise, the main story of the extended will be the building heat risk as the upper-level blocking high sets up over southeastern CONUS. Mid and long range models/ensembles continue to trend toward the higher heat and humidity building into the area more Monday and continue through much of next week. At this time, Monday is trending toward seeing triple digit heat indices, especially for western portion of the CWA. Then the ridge axis continue to amplify Tuesday through Thursday, with more widespread triple digit heat indices. Given the consistency, prolonged nature of this pattern along with this being the first heat wave of the summer, heat headlines are looking increasingly more likely for next week as this pattern becomes dangerous for vulnerable populations with health issues and/or lack of cooling/hydration.

Lastly accompanying this heat and humid pattern for next, will be daily chances for showers and thunderstorms as upper-level disturbance may overrun the ridge. If any showers/storms develop could end up disrupting the temp forecast and could lower heat indices with lingering clouds and rain cooled air.

Wagner

AVIATION

Issued 138 PM CDT Fri Jun 26 2026

Mid to high clouds will gradually clear out this evening and VFR conditions will prevail through the TAF period. Looking at lighter easterly winds tonight into Saturday morning. Easterly flow will continue through the day Saturday and gradually pick up a bit toward the late morning/early afternoon hours.

Wagner

MARINE

Issued 138 PM CDT Fri Jun 26 2026

High pressure over the the Great Lakes will keep winds lighter tonight into Saturday, but gradually pick up as the high pressure slides east. Will then see winds pick up for the later half of the weekend as low pressure deepens over the Plains and more southerly winds pick up for the start of next week. Could see stronger gusts up 30 knots at times as the heat waves persists across the region. With these gusty winds, small craft conditions will be possible at times through next week.

Wagner

MKX WATCHES/WARNINGS/ADVISORIES

WI...None. LM...None.