textproduct: Milwaukee/Sullivan

KEY MESSAGES

- An Extreme Heat Warning remains in effect for all of southern Wisconsin through Thursday evening. - Chances (40 to 70 percent) for thunderstorms later this evening into tonight. Best chances are north of a line from Lone Rock to Sheboygan. Some strong to severe storms with heavy rainfall may occur at times, mainly in the late evening. Damaging winds and large hail are the main hazards of concern.

- There are periodic chances (40 to 60 percent) for thunderstorms Thursday into the holiday weekend. Some strong to severe storms with heavy rainfall may occur at times, though confidence remains low with the timing of each round of storms. This may impact outdoor holiday activities at times, so keep up with the forecast.

UPDATE

Issued 742 PM CDT Wed Jul 1 2026

The Enhanced Risk by SPC shifted south a couple tiers of counties with the afternoon update. We had a couple of isolated storms in south central WI this afternoon, but they have since dissipated. We are currently watching storms that are developing along a boundary from Eau Claire to south central MN and another area of bubbly clouds over northeast Iowa. These will start to become more numerous as the low level jet kicks in this evening. The expectation is that clusters of storms will develop and track northeastward.

The next expectation, which seems a little overdone by some meso models, is that an outflow boundary from the organized clusters would help trigger convection into south central WI during the late evening. While the outflow is an idea, it seems less likely that it would develop and barrel into the ridge. The more likely scenario is that storms will continue to develop along the nose of the low level jet (LLJ) which is the IA/MN/WI border this evening, and then the LLJ will gradually lean over/veer into southern WI and help focus storm development in our area during the overnight hours.

So timing of this next round of storms into south central and southeast WI is quite uncertain. We can say that the earliest storms would make it into the Dells area would be 9 or 10 PM and probably midnight or later for Madison. As storms move in, they will encounter high CAPE (~2000 j/kg) and 35-40kt bulk shear which are sufficient for severe storms. Wind will be are biggest threat, then hail, but we cannot entirely rule out a tornado. As the night goes on, if convection continues along an east-west axis, heavy rain and localized flooding could be a concern.

Cronce

SHORT TERM

Issued 257 PM CDT Wed Jul 1 2026

Tonight through Thursday night:

We're in a short rain free period of the afternoon across southern Wisconsin. Don't expect this to last long across the area however. CAMs are really honing in on convection developing across northern IA and southeastern MN (maybe a few cells develop over far southwestern WI) late this evening into tonight. On the other hand WoFS is favoring more cellular convection developing late this afternoon and persisting into the evening. Given the unseasonably hot and humid conditions this is not a huge surprise to see the guidance become a bit overzealous, but as we begin to see the whites of the storms eyes here... its starting to look increasingly likely that there will be another round or two of strong to severe storms. The sfc front looks to remain to the the northwest of the MKX CWA. There are multiple outflow boundaries scattered across the area due to previous convection, which will provide some low level forcing should storms develop. With all the lingering boundaries, there is an agitated cumulus field on satellite currently in IA/southern WI (favors some of the WoFS cellular convection).

Now when it comes to the where of more thunderstorms, the ridge across the eastern CONUS remains in place with far southern and southeastern Wisconsin still under its influence. So ridge riding storms will be the main concern. Anything that begins to drift to the far southeast overtime should enter into a more stable airmass and decay. This is a prime area where the CAMs are struggling a bit as they try to make the storms go outflow dominate (this has been the case multiple days in a row, but the high pressure and stability are preventing anything from blowing into southeastern WI). The best potential for strong to severe storms overall still looks to be for areas along and north of a line from Lone Rock to Beaver Dam to Sheboygan. Should convection trend further south as the WoFs is suggesting then we will see this severe potential also shift south roughly from Platteville to Madison to West Bend.

CAPE is around 2000 J/kg (or better) for much of the area with bulk effective shear around 30-35 kts. Mid level lapse rates are marginal around 6 to 6.5 C/km while low level lapse rates are much better around 7 C/km. Given all of this, our main hazards are strong winds, hail, and heavy rain. Any storms that begin to train will pose a flood risk.

The linchpin pin here is the timing, which boils down to.. when does convection start to fire to our west along the sfc front. WoFS is favoring a slightly earlier timing in the late afternoon as it tries to get some cellular convection going, while other short term models hold off until roughly 9 PM to 11 PM for storms to be knocking on the door in Marquette, Green Lake, and Sauk Counties. Regardless of solutions here, storms are expected to continue through the overnight hours and may linger into early Thursday morning.

Additional rounds of rain and storms for Thursday through Thursday night will be possible (chances around 20-60%). The timing and placement of the storms will depend on how long convection lingers early morning Thursday and how much cloud cover remains. If skies clear quickly, then all of southern Wisconsin could get some scattered thunderstorms (with some stronger to severe storms possible). The exact location of the sfc boundary will play a big roll here as well. As it stands now, another unseasonably warm day with high CAPE and moderate shear. Best chances for storms look to be Thursday late afternoon into Thursday night.

The Excessive Heat Warning continues across southern Wisconsin into Thursday night. Generally the warmest conditions are expected across far southern and southeastern Wisconsin with slightly cooler conditions across central Wisconsin. This will be especially true for areas that receive rain as that will cool conditions for a bit. Thursday will be a bit cooler relatively speaking, but by and large high temperatures in the 90s with overnight lows in the 70s.

Patterson

LONG TERM

Issued 257 PM CDT Wed Jul 1 2026

Saturday through Wednesday:

The active weather stretch looks to continue into the weekend. Multiple rounds of rain and thunderstorms are expected both Saturday and Sunday.

The ridging across the eastern CONUS will begin to slowly breakdown Saturday, which will give the state a bit of a break from the scorching heat. While this takes the edge of the heat, this does open the door for active weather to persist. A slow- moving sfc boundary will slide into southern Wisconsin as the high pressure pulls away. As this boundary moves in there will be rain/storms chances 30-70% through the weekend. The better chances look to be Saturday vs Sunday. These better chances will associated with a shortwave trough that is expected to move across southern Wisconsin. The subsequent chances Sunday will depend on where the sfc boundary remains.

There will be a potential for some stronger to severe storms each day (with Sundays potential heavily depending on the after math of Saturdays). As things stand now lightning and heavy rain are by far the most pressing hazards. However, we are looking at some upper level support, unseasonably moist airmass, and forecast soundings showing some modest shear... if things align at the right time we could see some scattered strong wind and hail. We will be keeping a close eye on the holiday weekend with more information on the specifics of timing, location and severity to come. With a potentially active Fourth of July expected, take some time to make plans for the holiday now vs later.

Regardless of severity, heavy rain is likely with PWAT values around 1.5 to 2 inches. Any storms that begin to train over the same areas for multiple days could start to have flooding concerns. Thankfully everything at this time looks to be fairly progressive which will help limit the flooding potential.

Heading into early next week the low chances for rain look to linger a bit, but this is by and large due to the differences between models. Weak ridging is expected to settle in across the central CONUS with a low pressure system aloft in the Hudson Bay area for early next week. Each model has a difference solution here with the exact placement and strength of the low in Canada. The deterministic GFS even has a cut off low in the mid Mississippi. Given the uncertainty present low POPs around 20% or less does linger at times through early next week. Temperatures look to remain warm and more seasonable in the lower to upper 80s for next week. Overnight lows expected to be in the 60s.

Patterson

AVIATION

Issued 742 PM CDT Wed Jul 1 2026

VFR conditions expected overall, but MVFR possible in thunderstorms. Winds will remain out of the south-southwest through the TAF period. Thunderstorm chances will increase from west to east during the overnight hours. See the Update discussion above for more details. Another round of storms is looking likely over southern WI Thursday afternoon.

Cronce

MARINE

Issued 257 PM CDT Wed Jul 1 2026

High pressure around 30.1 inches will remain parked over the southern Appalachian Mountains into the weekend. Meanwhile, a low pressure system around 29.5 inches in west central Manitoba slowly moves east toward James Bay by Friday. Breezy south to southwest winds will persist through Thursday. Winds will approach but remain below Small Craft Advisory Levels through this evening in the nearshore waters. Southwest winds will weaken becoming light Thursday night through Friday. Heading into the weekend, high pressure in the Appalachian range will gradually shift east. As the high pressure pulls away, there is a potential for low pressure around 29.7 inches to move into the Great Lakes Region for the weekend.

Chances for thunderstorms (50-60%) remain across the northern half of the Lake through tonight. Tonight into Thursday morning there is a small chance (~20%) for rain and storms across the southern half. The chances for storms will persist through Thursday afternoon through Friday evening across the southern two thirds of the lake. Additional chances for rain/storms remains across the entire lake Saturday and Sunday.Strong to severe storms may occur at times, though confidence remains low in timing of stronger storms.

Patchy marine fog will be possible at times, primarily over the northern half of the lake as the warm and moist airmass moves over the lake.

Patterson

MKX WATCHES/WARNINGS/ADVISORIES

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