textproduct: Milwaukee/Sullivan

KEY MESSAGES

- Showers (60-90 percent chance) and scattered thunderstorms on Tuesday. Small hail expected with the thunderstorms.

- Widespread showers (80-90 percent chance) and scattered thunderstorms Wednesday and Wednesday night. Heavy rain and a conditional threat for severe thunderstorms is forecast.

- Winds and waves may approach Small Craft Advisory criteria Wednesday afternoon into Thursday.

- Next chances for thunderstorms develop Saturday and Sunday.

UPDATE

Issued 740 PM CDT Mon Jun 15 2026

No major changes to the going forecast. 18z guidance still resolves the LLJ southeast of the MN shortwave trough producing some widely scattered showers (or even weak thunderstorms) late tonight into early Tuesday morning. The intensity of that narrow LLJ increased just a bit, leading to wind shear being added to 3 of our TAF sites (KMSN, KUES, and KJVL).

The 18z guidance also depicts the aforementioned afternoon redevelopment, with some scattered showers expected and chances for thunderstorms, some of which could easily produce small hail given the low freezing levels for this time of year.

Sheppard

SHORT TERM

Issued 314 PM CDT Mon Jun 15 2026

Tonight through Wednesday Night:

Quiet weather will linger into this evening as high pressure continues to shift east overnight. During the pre-dawn hours on Tuesday, a compact shortwave is expected to move in from central Minnesota, bringing ~15 to 30% chances for light rain showers. There should be a bit of a lull in shower activity late Tuesday morning as early morning rain activity dissipates/pushes east and the shortwave closes into a compact upper low over NE Wisconsin. However, scattered shower and tstorm development is expected to increase Tuesday afternoon as daytime heating promotes steepening lapse rates in the low to mid levels. CAPE will be weak, only reaching 500 to 1000 J/kg amid weak effective shear of 15 knots. Storms will be poorly organized, but relatively low freezing levels may promote small hail for any stronger updraft, especially over southeast Wisconsin where there will be better opportunity for instability to build.

The wave will quickly move east and deamplify Tuesday night. Another larger trough is expected to rotate southeast out of the Northern Plains Wednesday morning and amplify through midday, increasing the upper level flow over the Corn Belt. The effects of the upper low will drive divergence aloft Wednesday morning and a large complex of storms is expected to become organized over northeast Iowa around 7am Wednesday. This complex of storms is then expected to continue ESE through the morning, barely grazing southern WI as it heads into Indiana.

Behind this morning complex, a surface warm front is expected to surge northward, driven by surface WAA ahead of an occluding low pressure center over the northern MS Valley. The position of this front will greatly determine where Wednesday afternoon's severe weather risk will occur. Some CAMs suggest the front will stay south of the WI/IL border, confining a severe risk to IL, while some show the warm front crossing into Wisconsin's southern row of counties. IF the warm front indeed does make it into southern WI, an all hazards severe risk would be possible along and south of the warm front Wednesday late afternoon and early evening as storms may latch onto the front itself. Given the disagreement among the CAMs, model trends will have to be watched over the next two days for a definitive forecast.

CMiller

LONG TERM

Issued 243 PM CDT Mon Jun 15 2026

A surface low pressure system is expected to move east toward Michigan Thursday morning, bringing a slight chance for precipitation in southeast WI (10-20%). Cold air advection will continue as a shortwave trough moving in from the northwest will intensify over the region Thursday afternoon. High temperatures are expected to be in the low 70s with dewpoints in the low 50s.

A region of high pressure is expected to build over the Plains Thursday night into Friday, but PW values of 0.7-0.9" and higher relative humidity values Friday morning could bring the potential for showers, although the chance remains low. Precipitation chances increase into Saturday (20-40%) as the high pressure systems moves off the Plains into the lower Mississippi River Valley. This chance increases further for Sunday (20-50%) as a cold front and a low pressure system move from the northwest into southern WI.

Monday's chances for precipitation decrease from Sunday as a shortwave ridge enters the region and the low pressure system sits south of WI.

Zawlocki

AVIATION

Issued 700 PM CDT Mon Jun 15 2026

VFR and quiet weather continue through the rest of this evening, with the FEW/SCT cumulus clouds eroding and lingering SCT (briefly BKN) higher altitude clouds over 20,000 ft. Surface winds decelerate and turn SW. As a shortwave trough sags southeastward from MN into WI, a narrow WSW LLJ is expected to produce 35-40kt winds at the 2,000ft level late tonight over portions of southern WI, yielding a brief window of LLWS (included in the KMSN, KUES, and KJVL TAFs). This same feature may kick-start some widely scattered showers or even weak thunderstorms, with PROB30 groups late tonight into early Tuesday morning included in the TAFs as it passes. VFR ceilings expected with this activity.

The aforementioned shortwave trough continues it's progression into southern WI (our region) Tuesday afternoon, with scattered showers expected and a chance for thunderstorms. These storms are generally expected to be sub-severe, but could easily produce small hail (due to the cold air aloft). Generally VFR ceiling altitudes with this activity, but cannot rule out some brief MVFR ceilings. Visibility may drop to MVFR (or even briefly IFR) with the heaviest showers / storms.

Sheppard

MARINE

Issued 241 PM CDT Mon Jun 15 2026

Southwesterly winds shift southerly into early Tuesday as a low pressure system deepens over northern Lake Michigan (29.65 inches), shifting eastward over the northern half of the lake Wednesday morning, with winds becoming northwesterly Wednesday. Scattered showers and storms over central and southern Lake Michigan Tuesday night through Wednesday.

Following the chance for precipitation, a low pressure system will move over Lake Michigan Thursday morning (29.47 inches), causing a wind shift from southeasterly Wednesday night to northwesterly Thursday morning, with the potential for breezy conditions.

A high pressure system will move in Friday, creating continued breezy, westerly winds, primarily over the southern half of Lake Michigan.

Zawlocki

MKX WATCHES/WARNINGS/ADVISORIES

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