textproduct: Milwaukee/Sullivan

KEY MESSAGES

- A very humid airmass will return Monday and Monday night ahead of approaching low pressure with widespread showers and scattered thunderstorms forecast.

- Hot and humid conditions expected mid to late week, with some potential for Heat Advisory conditions and additional chances for showers and storms.

SHORT TERM

Issued 1250 AM CDT Sun Jun 7 2026

Today and Tonight:

Broad high pressure over the Great Lakes and broad low pressure over the Great Plains will drive a light east to southeasterly breeze over southern WI today, with the onshore flow holding eastern WI temperatures to the 70s, with inland highs in the mid 80s. Similarly, the lake will limit / inhibit shower and storm chances for eastern and central WI, while far southwestern WI (Lone Rock to Monroe westward) observes a chance for showers and thunderstorms this afternoon (30-60%). 30-50% shower and storm chances spread northeastward late tonight ahead of an approaching shortwave trough.

Sheppard

LONG TERM

Issued 1250 AM CDT Sun Jun 7 2026

Monday through Sunday:

Synopsis: The 300-250mb upper air pattern through this week will feature a longwave trough over the northern rockies and ridge over the Great Lakes region, with the axes of each slowly progressing eastward. For Wisconsin (and the midwest in general) we can expect to see several shortwave troughs (and surface pressure responses) rippling through the east edge of the longwave trough from SW to NE, yielding periodic chances for showers and thunderstorms. The ridging and warm weather should peak mid-week (Wednesday), followed by a slight cooling trend into next weekend.

Details: The first 500mb shortwave trough slowly crosses WI Monday morning through late Monday night, with one or more rounds of scattered showers and thunderstorms expected to track northward across the region through said timeframe (overall precip chances 85-95%). Monday is not a 'complete wash' due to the off-and-on / showery nature of this activity, but we're fairly confident that most areas in southern WI will see at least some rainfall at some point on Monday / Monday night (hence the high precip chances). A modest southeast breeze off of Lake Michigan will limit instability over much of southern WI, hence we do not currently anticipate any strong to severe storms. The highest thunder potential would be found over southwestern WI.

For Tuesday, models keep the 500mb isohypses fairly straight, and the pattern free of noteworthy shortwaves. Hence, only 20-30% chances for precip through the daytime hours, mainly in the event the lake breeze were to initiate convection in far eastern WI. Of course, this could change in future model runs. High temperatures climb into the upper 80s to around 90, cloud cover decreases. Precip chances climb to 25-40% late Tuesday night on account of potential for a decaying storm complex to approach from the west (depicted in the 12z ECMWF forecast).

The warmth should peak on Wednesday with high temperatures in the low 90s possible. GEFS instability peaks on Wednesday as well, with ~80% chances of reaching or exceeding 3,000 joules CAPE in the afternoon. A 500mb shortwave may kick-off convection west of our region Wednesday afternoon, with a chance for it to track east and decay into our region Wednesday evening / night (45-80% precip chances, highest further west). Note that a slight eastward shift in the positioning of that trough (and the wind shear + convective initiation) would yield a more substantial threat for organized / strong storms tapping into the instability overhead. This is something we'll have to watch for, but fortunately, the timing and placement of initiation with the latest guidance suggests the higher threat will be centered closer to Minnesota as opposed to Wisconsin.

Deterministic GFS / ECMWF runs resolve a more potent 500mb shortwave crossing our region Thursday, which could refocus the wind shear + ascent over WI and yield a more potent severe weather threat. Our precip chances for Thursday remain at ~60% due to dispersion / uncertainty amongst the ensemble guidance. In other words, this shortwave could time itself favorably with the diurnal heating cycle, or unfavorably.

A gradual cooling trend is then expected late this week into next weekend as the longwave trough builds in from the west.

Sheppard

AVIATION

Issued 1250 AM CDT Sun Jun 7 2026

Dry weather and VFR continue through the rest of the overnight hours. Some marine fog may develop over north central Lake Michigan and drift towards the shoreline of east-central WI, but should not affect eastern WI terminals.

There will be some 10-50% chances for a stray shower or thunderstorm in far southwestern WI through this afternoon and evening (southwest of all TAF sites, mainly KMRJ and KEFT airports), with dry weather and continued VFR elsewhere. Shower and storm chances will slowly build northeastward towards I-90 late tonight, then across the rest of the region Monday into Monday night.

Sheppard

MARINE

Issued 1250 AM CDT Sun Jun 7 2026

High pressure of 29.9 inches builds into the Upper Great Lakes and strengthens to 30.1 inches overnight. Warm and humid air will linger over the relatively cool waters of Lake Michigan, with a plume of marine fog over north-central portions of the lake slowly sagging southwestward overnight. A Marine Dense Fog Advisory remains in effect for the northern 2/3 of the lake until midday Sunday. Recent satellite observations suggest the extent / intensity of the fog may be weaker than prior expectations, hence the Advisory may be canceled early.

Light and variable winds (predominantly north to northeast) continue throughout Sunday. Broad low pressure over the Great Plains and high pressure over the northeastern CONUS will lead to modest southeast winds over the lake late Sunday night through Tuesday.

Occasional chances for showers and thunderstorms are in the forecast, particularly late Monday through Monday night. Additional chances later in the week.

Sheppard

MKX WATCHES/WARNINGS/ADVISORIES

WI...None. LM...Dense Fog Advisory...LMZ643 until 9 AM Sunday.

Dense Fog Advisory...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565- LMZ567-LMZ669-LMZ671-LMZ868-LMZ870-LMZ872 until 1 PM Sunday.