textproduct: Milwaukee/Sullivan

KEY MESSAGES

- Showers (45-65 percent chance) and scattered thunderstorms this afternoon. Small hail expected with the thunderstorms.

- Widespread showers (80-90 percent chance) and scattered thunderstorms Wednesday and Wednesday night. Heavy rain and a conditional threat for severe thunderstorms is forecast.

- Winds and waves may approach Small Craft Advisory criteria Wednesday afternoon into Thursday.

- Next noteworthy chance for thunderstorms is Sunday.

UPDATE

Issued 608 AM CDT Tue Jun 16 2026

The initial line of showers associated with warm advection ahead of the approaching trough will continue eastward across the eastern forecast area early this morning. After at least partial clearing behind these showers, clouds will move back in by late morning as the trough pushes in from the northwest. Additionally, scattered showers will accompany the trough, with some thunder possible by early afternoon with the trough axis overhead. Still think some small hail will be possible with any afternoon storms. Bumped temps down a bit in the northwest given the small window of opportunity for sunny skies ahead of the trough. Otherwise, the forecast looks on track for the upcoming day.

DDV

SHORT TERM

Issued 100 AM CDT Tue Jun 16 2026

Today through Wednesday night:

Through the predawn hours today, a compact shortwave is expected to track southeast from MN into northwest WI, inducing a narrow LLJ over eastern IA and southern WI. The associated WAA may develop some widely scattered rainshowers (or even weak thunderstorms) in the region between roughly 3 AM and 9 AM this morning. A lull in the shower activity would then be likely late this morning as this activity pushes east over Lake Michigan.

The shortwave trough closes off into a compact upper low over central portions of WI throughout the day today, slowly tracking east. The relatively cool air aloft, preexisting modest mid-level lapse rates, and sharpening low-level lapse rates (through the course of daytime heating) should allow this feature to produce a second round of showers and thunderstorms this afternoon (Noon-7PM), this time with greater coverage. The relatively low freezing levels (beneath 8,000 ft at times) should allow any thunderstorm cells to produce small hail. Dry weather returns this evening.

As another 500mb trough tracks southeastward across the Dakotas tonight, diffluent flow overspreads Iowa and an MCS evolves. 00z model guidance depicts this MCS tracking eastward into southern WI and much of IL, arriving between 5-9 AM Wednesday morning. With HREF Mean MUCAPE under 1,000 joules in our region and substantially higher into IA/IL, it would appear that the majority of the stronger / severe storms will dive south of our region, leaving sub-severe storms (still plenty capable of lightning and possibly brief heavy rainfall) to overspread our region Wednesday morning.

Deep surface low pressure behind the MCS will then attempt to draw the effective warm front (and instability plume) northward into far southern WI Wednesday afternoon. The 00z HREF's best guess is that the warm front will setup just south of the WI/IL border and shield us from surface based convection (and thus reduce severe wx potential), but as stated during the prior forecast iteration, a small shift in the MCS or low pressure system track could still bring the warm front as far north as southern WI, yielding an all-hazards severe threat south of the I-94 corridor. Stay tuned to this forecast, as details can and will change.

Sheppard

LONG TERM

Issued 100 AM CDT Tue Jun 16 2026

Thursday through Monday:

Predominantly dry weather expected in the cool sector of the departing low pressure on Thursday. Some lingering 500mb vorticity on the north edge of the jet, some cool air aloft, and steepening low-level lapse rates through the course of diurnal heating (below the subsidence inversion) allows models to yield some low chances of cellular rain showers Thursday (~10-15% chance). A similar story for Friday, not enough jet dynamics to support much else. Ensemble plots for High Temps suggest a daytime high around 70 / low 70s for Thursday, with only a very slight overall warming trend this weekend into early next week (ensemble mean high temps centered in the mid 70s, with growing dispersion).

For Saturday, the longwave trough axis centered over our region begins to exit east (hence the slight warming trend). Warm/moist return flow over the Great Plains sets up a NW to SE oriented baroclinic zone from southern MN into eastern IA / northwest IL (and perhaps southern WI), which leaves the potential for a ridge-riding shortwave to kick-off an MCS Friday night and track it along that gradient towards our region Saturday morning. The models (for now) suggest that the gradient and MCS (as seen in QPF output) will setup southwest of us, though we have some 20-30% precip chances across our CWA just in case.

Our next noteworthy chance for thunderstorms arrives Sunday, with plenty of uncertainty as to how things will shake out. Multiple ECMWF Ensemble Members track an organized low pressure system northeast from the Central Plains towards southern WI (a setup which would leave organized thunderstorm chances on the table), whereas several GEFS members track the low through Illinois, leaving us with no southerly return flow. A large subset of members from each modeling system stalls the low over the Central Plains, leaving the baroclinic zone northeast of it and any corresponding satellite low pressure to attempt a northward push of moisture / QPF into our region. All this to say the predictability is very low, but there are chances for showers and thunderstorms Sunday.

Sheppard

AVIATION

Issued 608 AM CDT Tue Jun 16 2026

Scattered showers across the east early this morning will be followed by a brief break in clouds and precip ahead of an approaching trough. Showers will move back in from the northwest mid to late morning along with mostly cloudy skies. Ceilings may briefly drop to MVFR as the trough arrives, mainly northwest of Madison. Scattered showers will then progress across the forecast area late morning into the afternoon, with some thunder and small hail also possible by afternoon.

Dry weather this evening into at least early tonight will give way to increasing chances for showers late tonight into Wednesday as the next trough approaches. More widespread precip and lower clouds are expected with the system tomorrow.

DDV

MARINE

Issued 100 AM CDT Tue Jun 16 2026

Southwesterly winds shift southerly early this morning as a low pressure system deepens over northern Lake Michigan (29.5 inches). Winds become relatively light and variable underneath it (northern half of the lake) later this afternoon, with winds veering west over the southern half. Showers and thunderstorms will be possible across the lake through the daytime hours today, a couple of stronger cells this afternoon could produce small hail.

A weak surface ridge crosses the lake tonight, with winds subsiding and backing southwest. A much more organized low pressure system (29.2 inches) will then track eastward from around South Dakota, crossing Lake Michigan Wednesday evening. Ahead of it's arrival, we expect gusty southeast winds Wednesday morning and afternoon (particularly over the southern half of the lake) with increasing chances for thunderstorms, some of which could be strong (particularly over far southern portions of the lake). Breezy west to northwest winds are expected Wednesday night into Thursday as the low exits east. This same breeze then continues into Friday (albeit weaker) as weak high pressure builds into the region from the west.

Sheppard

MKX WATCHES/WARNINGS/ADVISORIES

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