textproduct: Milwaukee/Sullivan

KEY MESSAGES

- Extreme Heat Warning in effect for all of southern WI tonight through Wednesday evening. Additional heat headlines may be needed for the second half of the week, but some uncertainty remains due to clouds and rain chances.

- Thunderstorm chances return this evening through the end of the week as the hot and humid pattern continues. Best chances are tonight (mainly north of a line from Lone Rock to Fond du Lac), through Friday on a more areawide basis. Strong to severe storms may occur at times.

SHORT TERM

Issued 255 PM CDT Tue Jun 30 2026

Tonight through Wednesday night:

Hot and humid conditions continue into tonight with heat index values remaining in the 100 to 105 range. Tonight, heat will remain a concern, as overnight lows will only drop into the mid to upper 70s.

The ridge held fast through today keeping storm activity north of the area, but tonight, models depict some storm activity over central increasing through the overnight hours as the environment uncaps and the LLJ kicks off convection. Storm motion vectors would carry any storms over central WI to the northeast sparing most of the area, but areas north of a line from Lone Rock to Fond du Lac may see a glancing blow from thunderstorm activity. Given the steep mid level lapse rates, large hail may occur with any storms, and there may be some wet microburst potential give the high PWATs and low shear. This activity would move through just before and just after dawn on Wednesday.

After morning thunderstorm activity, more hot and humid conditions are expected with highs in the low to mid 90s, with heat indices above 100.

CMiller

LONG TERM

Issued 256 CDT Tue Jun 30 2026

Thursday through Tuesday:

The upper level ridge begins to flatten Thursday allowing more thunderstorm activity into the area. There looks to be some potential for a morning round, followed by a late afternoon and evening round. The latter round may feature more of the severe threat, given the potential for instability to build through Thursday.

Beyond, the ridge sinks southward, allowing a more favorable band of flow aloft to pass over the area into the weekend. Daily thunderstorm chances look possible, but each days chances will be highly dependent upon where the previous day's rounds of storms force an outflow boundary to flow and act as a storm trigger. As such a high amount of uncertainty will linger into the 4th of July weekend regarding storm timing/position.

Hot and humid conditions will linger through Friday. with highs near or into the 90s. Temps "cool" this weekend with highs in the 80s, but dewpoints will remain elevated into next week, prolonging the mugginess.

CMiller

AVIATION

Issued 253 PM CDT Tue Jun 30 2026

Breezy southwest winds continue this afternoon amid a mixture of MVFR cigs and SCT to CLR skycon in some spots. Cumulus clouds and wind will linger until sunset, when daytime mixing subsides.

Overnight, thunderstorms activity may for over west central WI, adding high cirrus to the skies. Storms are mainly expected to stay north of a line from KLNR to KFLD tonight into early Wednesday.

Storms are expected to move off by late Wed morning and then a similar mix of VFR and MVFR conditions may take hold again tomorrow afternoon.

CMiller

MARINE

Issued 245 AM CDT Tue Jun 30 2026

Modest to breezy southerly winds will prevail into Thursday then lighter into Friday as high pressure remains to the southeast of the Great Lakes, while troughs of low pressure continue over Canada into the northern Great Plains. Scattered thunderstorms are forecast across the northern half tonight through Wednesday night, and across the southern two thirds Thursday into Friday, and across the whole lake Friday into Saturday as a cold front shifts winds to northerly. Patchy marine fog will be possible at times, primarily over the northern half of the lake, as a warm moist air mass moves over the lake.

CMiller

MKX WATCHES/WARNINGS/ADVISORIES

WI...None. LM...Small Craft Advisory...LMZ643-LMZ644-LMZ645-LMZ646 until 10 PM Tuesday.