textproduct: Milwaukee/Sullivan

KEY MESSAGES

- An Extreme Heat Warning remains in effect for all of southern Wisconsin through this evening.

- After morning showers and thunderstorms end, a brief break will allow for additional storms to strengthen late this afternoon into this evening. All hazards are possible. Storms will weaken overnight. Early Friday morning a decaying line of storms may also progress eastward through the region.

- There are periodic chances (40 to 60 percent) for thunderstorms throughout 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, so keep up with the forecast.

UPDATE

Issued 615 AM CDT Thu Jul 2 2026

Showers are storms are in a weakening trend as they move southward and the LLJ weakens into this morning. Very high PWAT values around 2 inches will lead to the main concern this morning being locally heavy rain and perhaps a few areas of local flooding. However, with cells struggling to maintain intensity not expecting this threat to be widespread. Primary concern will be where training storms develop.

As showers and storms decay this morning, expecting the remnant boundary to push back northward, allowing for an increase in instability and temperatures. Areas in central Wisconsin may struggle to see clouds dissipate, and therefore may have the Extreme Heat Warning downgraded or canceled in that area. With a strong EML still in place through Illinois, at this time cannot rule out clouds dissipating all the way northward, so have kept the Extreme Heat Warning out for all of southern Wisconsin. Keep an eye out for updates and cancellations as the cloud cover shows its hand this afternoon.

This evening, the remnant boundary will be the focal point of developing additional storms. With CAPE over 2000 J/kg, shear of 35-40 kt, and still impressive PWATs between 1.5 and 2 inches, expecting all hazards to be possible with storms that develop.

MH

SHORT TERM

Issued 1139 PM CDT Wed Jul 1 2026

Overnight through Friday:

Thunderstorms congealed into somewhat of a line over central and southwest WI this evening. There are a few segments that are tracking west to east that are organized, cold-pool-driven and producing 40 to 60 mph winds. As these storms track into portions of southern WI overnight, our environment support wet microbursts with its mid level dry air, high instability, and sufficient shear. Wind is our main concern. The northern two tiers of counties (north of Madison and Milwaukee) are in a Severe Thunderstorm Watch until 5 AM. The late end time on this is to allow for storms to get across most of Lake Michigan.

As the night goes on and the cluster of storms takes on a more east-west orientation, we are going to have an increasing flooding risk. With PWATs pushing 2 inches, individual storms can have 1 to 2 inch per hour rain rates, and repeated rounds of these storms with high rainfall rates will quickly add up.

Thursday (today): A shortwave tracking through the Midwest is expected to arrive in southern WI during the afternoon which should trigger thunderstorms. If the overnight showers/storms diminish in a timely manner this morning, this will give us enough time to clear out and destabilize. The more sun, the higher the instability for stronger storms. Overall, there will be decent synoptic forcing to support a cluster of storms, including the right entrance region of the upper jet, the nose of a low level jet, and the mid level shortwave trough. With high cape and marginal shear, wind and hail are the main threats.

Cronce

LONG TERM

Issued 1139 PM CDT Wed Jul 1 2026

Friday through Saturday:

The surface high that was sitting over the southern Appalachians will gradually weaken and shift toward the Atlantic coast Friday through the weekend. This breaking down of the upper ridge will transition us to zonal flow across the Upper Midwest. Weak ripples (shortwave troughs) in the mid level flow will help to trigger rounds of thunderstorms Friday through Saturday night. This is a weather pattern where the timing of these ripples is uncertain. In addition, the focus of each consecutive round of storms would likely be along an outflow boundary from the prior round of storms, so the location is also uncertain (could end up being in northern IL rather than southern WI).

For Friday, another shortwave is expected to track across central or southern WI during the day. With southern WI on the periphery of the high heat and humidity (instability gradient), we have a risk for severe storms. The timing and location remain uncertain.

The heat on Friday is also uncertain, as it will depend on where that Thursday night outflow boundary rests and ultimately how much sun we get. It is possible that only a portion (or none) of southern WI would need a heat advisory.

We have been watching a fairly consistent signal for a robust shortwave trough to track across WI on Saturday. This would likely occur during the afternoon at the time of peak daytime heating, but that is uncertain. The GFS is showing an MCS that could roll across southern WI Saturday morning, so that could put a damper on the severity of any storms that develop with the afternoon shortwave. Again, we will need to wait until the prior day to get a better handle on timing. I realize this is a critical time for making decisions about outdoor events and activities during this Independence Day holiday weekend and it is frustrating to not have all the information ahead of time. It is important to have a plan in case of thunderstorms, including severe.

Sunday through Wednesday:

One more shortwave trough and associated weak surface low is expected to cross northern WI and Upper Michigan on Sunday. Higher chances for showers and storms will be closer to this low to our north, but steep low-mid level lapse rates in this cyclonic flow will give us scattered shower chances all the way down to the IL border. This low may take until Monday to clear the Upper Great Lakes.

A welcomed return of slightly cooler and drier air is slated to arrive by Monday. The weather should be dry Monday and Tuesday, but another shortwave trough could bring showers and storms again by Wednesday. We will still be warm and humid, just not very hot like it has been.

Cronce

AVIATION

Issued 615 AM CDT Thu Jul 2 2026

VFR to MVFR ceilings this morning, with a few heavier storms producing visibilities below 2 SM through the morning hours. Clouds will become VFR again and scatter out through the afternoon before additional storms develop late this afternoon through tonight. Generally expecting VFR ceilings, but will see local drops to MVFR and below similar to this morning. With the afternoon and evening storms, damaging winds, large hail, and an isolated tornado are all possible. Storms will become a line into the late evening hours and transition to a wind threat, moving eastward into Lake Michigan late tonight. Going into early Friday morning, an additional line of storms may move eastward through the region, but confidence in impacts is low at this time. Storms diminish into the mid-morning hours once again.

Generally southwesterly winds through today outside of storms, with sustained winds around 12 kt during the afternoon hours. Winds remain southwesterly through Friday morning, but will decrease to less than 10 kt overnight.

MH

MARINE

Issued 1139 PM CDT Wed Jul 1 2026

High pressure will remain parked over the southern Appalachian Mountains into the weekend. Meanwhile, a low pressure system around 29.5 inches will track across Ontario and reach toward James Bay by Thursday night. Breezy south to southwest winds will persist through Thursday. 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 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 (30-60%) will persist from Thursday afternoon through Friday evening. 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 overhead.

Cronce

MKX WATCHES/WARNINGS/ADVISORIES

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