textproduct: Milwaukee/Sullivan

KEY MESSAGES

- Expecting hot and humid conditions through much of this week leading to dangerous heat index values and associated risks, such as heat exhaustion and heat stroke. Heat headlines are expected for much of the week. An Extreme Heat Watch is in effect Monday into Monday night.

- Chances for storms this morning west of the Kettle Moraine, with additional storm development tonight across areas northeast of the I-90/I-94 corridor.

- Moderate to high swim risk will develop late tonight through Monday for building waves in Ozaukee and Sheboygan Lake Michigan beaches. A Beach Hazards Statement may be needed.

- Chances for showers and storms increase a bit for mid to late week.

UPDATE

Issued 708 AM CDT Sun Jun 28 2026

MCS currently over south-central Wisconsin is continuing to maintain intensity. Still anticipating developing EML over Wisconsin to prevent strong storms, but cannot rule out rain and storms across southwestern to south-central midday onward with the main hazard expected to be lightning and an outside chance of remaining damaging winds. Overnight 00Z and 06Z meso models have continued to develop scattered thunderstorms along a warm front draped across central Wisconsin, bringing additional lightning and potential for elevated storms bringing hail. If LLJ dynamics can fire enough storms in central Wisconsin, a wind threat also becomes possible. Overnight tonight, an elevated swim risk also develops for Lake Michigan beaches in Ozaukee and Sheboygan Counties. Stay out of the water and away from dangerous areas like piers and breakwalls!

MH

SHORT TERM

Issued 1217 AM CDT Sat Jun 27 2026

Today through Tuesday:

Light enely surface winds will continue early this morning as high pressure remains over the nrn Great Lakes and srn Ontario. A weak 925-850 mb sely flow will begin the warm, moist advection aloft and bring north some scattered to sometimes broken stratus from nrn IL this morning. Some of these clouds could linger through mid to late morning before dissipating.

For this afternoon, a decaying MCS is expected to mostly dissipate as it moves into sw and south central WI. 850-700 mb warm, moist advection will support the MCS across srn MN in the morning, but it begins to run into very warm and dry mid level air that will already be in place across srn WI by late this morning into the afternoon. Only 20 percent chances for showers and storms is forecast west and north of the MKE metro area.

The low to mid level warm advection will increase late this afternoon through Mon AM as the high amplitude upper ridge builds into the Great Lakes. The surface warm frontal passage is expected Mon AM. Only 20-30 percent chances of showers and storms are forecast tnt toward central WI, as the very warm and dry 700 mb air will attempt to inhibit elevated convection. A hot, humid, and capped airmass will finally arrive by Mon afternoon with high temps in the lower to middle 90s and dewpoints in the lower to middle 70s. This will yield heat index values of 100-108F with similar values expected for Tue.

Gehring

LONG TERM

Issued 1217 AM CDT Sat Jun 27 2026

Tuesday night through Saturday:

The heatwave will continue much of the week. The strong upper ridge axis will gradually shift to the east and south becoming a west to east upper ridge from the ern Ohio Valley to the ern Seaboard by Wed and lasting through the week with only minor weakening. Meanwhile a series of shortwave troughs will continue to traverse from the wrn USA into the Upper MS River Valley and nrn Great Lakes. Thus the storm track will mainly remain to the west and north of srn WI with 500 mb heights at 588 DM or greater. This continues to place a hot and humid airmass over srn WI through the week. Extreme Heat Warnings or Heat Advisories will likely be needed much of the week. Only small chances for showers and storms toward central WI for Tue nt-Wed with chances increasing a bit for the remainder of the week.

Gehring

AVIATION

Issued 708 AM CDT Sun Jun 28 2026

VFR conditions expected through the majority of today, with MVFR visibilities possible under storms moving eastward through southwestern to south-central Wisconsin midday through this afternoon. These storms will become capable of producing lightning and some potential for briefly gusty winds. Outside of storms, expecting increasing southeasterly winds throughout today, with gusts around 20 kt developing during the afternoon and evening. Expecting additional storms to develop overnight, but for coverage to be low (20-40%). Lower ceilings in MVFR to fuel alternative are expected as these storms develop. Winds will shift to southwesterly into Monday morning.

MH

MARINE

Issued 1217 AM CDT Sat Jun 27 2026

High pressure around 30.0 inches is expected to linger across the northern Great Lakes and southern Ontario through this morning, with light north to northeast winds, becoming easterly later today. Low pressure will then deepen to around 29.3 inches over the central high plains by this evening, shifting winds to the southeast over the lake. Winds then shift more southerly and increase into Monday, as the low lifts into the Canadian Prairies by Monday evening, and a warm front passes north across the lake. Breezy southerly winds will continue through at least Wednesday as low pressure stalls over Canada.

Gehring

MKX WATCHES/WARNINGS/ADVISORIES

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