textproduct: Milwaukee/Sullivan

KEY MESSAGES

- Extreme Heat Warning in effect for all of southern WI today 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 Wednesday night through Friday. An isolated storm during this period may become severe.

UPDATE

Issued 646 AM CDT Tue Jun 30 2026

Some chances for showers and storms in central to southwestern WI today, with a lingering EML/warm nose preventing the majority of development. However, a high amount of CAPE (over 3000 J/kg) is available for any storms that do punch through the EML. This would require a strong forcing mechanism, which is currently lacking. Right now, expecting any showers/storms to develop off of outflow boundaries, so should remain generally cut off from surface instability and sub-severe.

MH

SHORT TERM

Issued 1142 PM CDT Mon Jun 29 2026

Tonight through Tuesday:

Low pressure around 991 mb continues to deepen over srn Manitoba and will deepen to 985 mb over sw Manitoba by 12Z Tue as the main upper wave swings nwd from the Dakotas. The initial squall line ahead of the cold front in sw MN has mostly dissipated, but there is shower development within the low level jet axis over ne IA into west central WI but moving newd. Thus the night is looking mainly dry but muggy for srn WI. Otherwise sswly sfc winds will maintain a hot and humid airmass over srn WI into Tue and Wed. The Extreme Heat Warning is in effect through Wed at this time.

Showers and storm chances of 20-40 percent are forecast Tue nt along and west of a line from Darlington to Madison to Sheboygan then shifting even farther toward central WI on Wed as the main shortwave track runs from the central Great Plains to MN and nrn WI. The flow aloft then becomes more wswly for Wed nt-Thu with a vorticity maximum in the flow. Less capping and high CAPE will remain with 60-80 percent chances for showers and storms mainly over south central WI with much lower chances toward MKE. Some of these showers and storms could linger into Thu.

Gehring

LONG TERM

Issued 1142 PM CDT Mon Jun 29 2026

Thursday night through Monday:

500 mb cluster analysis is generally showing positive anomalies over and north of the western Great Lakes region Thursday night into Saturday night, with a modest ridge remaining just east of the region. There should still be west northwest flow over the region during this time, with various 500 mb vorticity maxima shifting through at times. At the surface, a stalled warm front may remain over or near the area Thursday night into Friday, lingering into Independence Day or Saturday night per ensemble mean output from the ECE/GEFS.

The low level jet may pivot more over the area during this period, helping to maintain warm, moist advection. This should continue to support periodic rounds of showers and thunderstorms Thursday night into Saturday night. Ensembles show most members with measurable precipitation as well. Temperatures and heat index values during this time will be highly dependent on clouds and precipitation. Still, very warm and humid conditions are expected to continue through this period and are supported by ensembles.

The 500 mb ridge axis should shift further east Sunday into Monday, and may allow for high pressure to build in. This may allow for some drier conditions to work into the area at times, and chances for showers and storms may lower in later forecasts if this trend continues. It will remain warm and humid during this time.

Wood

AVIATION

Issued 646 AM CDT Tue Jun 30 2026

VFR conditions are expected throughout today into Wednesday. Southwesterly winds will become gusty at 20-25 kt by midday. Winds will diminish to become steady at 10-12 kt overnight, with LLWS around 40 kt developing across much of southern Wisconsin during this timeframe. Winds will remain light around 10 kt and LLWS will diminish into Wednesday morning.

MH

MARINE

Issued 1142 PM CDT Mon Jun 29 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 Great Plains. Areas of dense fog may develop at times this week due to a very humid airmass flowing over the cooler waters of the lake. Scattered thunderstorms are forecast on most days, especially over the north half.

Gehring

MKX WATCHES/WARNINGS/ADVISORIES

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