textproduct: Milwaukee/Sullivan

KEY MESSAGES

- Increasing humidity and thunderstorm chances for late tonight through Saturday. A 1 out of 5 (marginal) risk for severe storms is forecast Friday, but the timing and likelihood of the severe potential remains in question.

- Trending less likely for storm chances through the rest of the weekend. Not an all day wash out, but can't rule out some showers and storms at times.

- Next round of rain is expected early next week.

- Hot and humid conditions expected mid to end of next week

UPDATE

Issued 555 PM CDT Thu Jun 4 2026

Forecast details from the early afternoon discussion remain on track this evening, save for recent trend in the CAMs for a slightly later arrival to convection overnight. CAMs now favor an arrival of rain in SW to south central WI around 3am as the rain battles large dewpoint depressions over southern WI.

CMiller

SHORT TERM

Issued 200 PM CDT Thu Jun 4 2026

Tonight into Saturday:

The main focus is on the thunderstorm chances through Saturday as a pair of mid level shortwave troughs propagate through the Upper Midwest.

Currently, SW to NE oriented frontal boundary region is fairly evident from the convection that has developed from NW WI down through central IA and the Omaha area. This forcing is tied to a mid level shortwave trough currently observed west of this region which will track east through southern WI tonight into Friday morning and provide our next chances for rain/storms. HRRR/RAP has been fairly consistent today with this SW to NE band of rain/embedded storms to drift east into SW/SC WI until around midnight. Through the early morning hours Friday, the low level moisture (925-850mb) transport kicks in and should provide a secondary surge to the convection and help it to become a bit more widespread into daybreak. Instability is fairly minimal as this wave comes through with the 04.17Z RAP showing only a few hundred J/kg of 0-3km MUCAPE available to be tapped into. The main question is how much rain will fall given our rapid onset into drought over the past month. The 04.06/12Z HREF has shown about 70-100% probabilities of hitting at least 0.25" of rain across all of southern WI with the more widespread chances of hitting it going from SW to C WI. Getting between 1 to 2" seems to be around the high end of the rain potential for this event which coincides with the higher PWs that will be advected in with this air mass overnight.

Once this feature/trough tracks off to the east Friday afternoon, the focus will then go to the north as a secondary mid level trough currently over Montana which will quickly propagate eastward into the northern Great Lakes by late Friday. At the surface, a low should skirt the US/Canadian border as a cold front drops southeast across Minnesota and northern Wisconsin. Expect that there'll be some convection that develops along that feature which could push something through central WI (Marq/GL/FDL/Sheb co.) in the evening hours. Instability and shear looks a bit better for this situation, which is what the Day 2 Marginal risk covers for us. Can't rule something out, but at this point isn't looking very likely or widespread.

Going into Saturday, still a bit uncertain as the 04.12z NAM/GFS/EC all show some sort of QPF in southern WI which is likely tied to that trough/front coming through. Have left some POPs in there to cover this feature, but overall thinking is that while we have chances for showers/storms out there that it won't be an all day rain situation beyond the Friday morning stuff. Has a bit of a decaying MCV look to it from the convection that develops in central Iowa early Saturday. Will have to play this one day at at time right now since what happens tomorrow will have an impact on the subsequent days.

One thing that does look certain is that it will be more humid as surface dew points climb into the 60s as the rain moves in overnight into Friday.

Halbach

LONG TERM

Issued 200 PM CDT Thu Jun 4 2026

Saturday night through Thursday:

The main initial focus for any rain/convective development will be focused along a west to east oriented front set across southern Iowa into central Illinois on Saturday night. As the core of the ridge of high pressure drifts east across the Great Lakes on Sunday, the western wing of this belt will lift northward as the return southerly low level flow advects a warmer and more moist air mass back into southwest Wisconsin. Much of this broad, southerly low level flow is due to a cut off mid level trough currently observed over northern Mexico which will get picked up and propagated northeastward through the Plains into early next week. Some discrepancies exist between the GEFS/ECMWF for the exact track that this feature takes, but they all at least pull it northward and should bring the next chances of rain along with it. Instability is a bit in question along with weak mid level flow associated with the system, so am not currently expecting severe potential with it, but details can change over time and will follow the trends with it.

Beyond that, consensus shows a rather deep and cut off mid level trough taking hold in the western US putting the Great Lakes region into the belt of southwesterly mid level flow and strong low level flow which will bring hot and humid conditions in from mid week onward. With high temps expected to get into the 90s and dew points pushing the low 70s, we could be looking at heat advisory level (HI 100F+) conditions over this period. The main thing that is uncertain is with those dew points as they can trend a bit high in the extended period and they may end up lower.

Halbach

AVIATION

Issued 608 PM CDT Thu Jun 4 2026

VFR conditions should persist through sunset, but lower ceilings are expected to slowly move in from the west as widespread rain along a frontal boundary slowly moistens the lower atmosphere and moves east. Some combination of MVFR west of KMSN and VFR east of KMSN should exist late this evening through 06Z, then MVFR and IFR ceilings will push east 06-12Z as rain and thundersorms push in.

Rain and thunder should persist through the morning hours on Friday, pushing east Friday afternoon. Low ceilings are then expected to rise and scatter late Friday afternoon.

Winds will remain southerly to southwesterly tonigh through Friday and light to moderate. Some gusts to 20 knots may occur Friday late morning into the afternoon.

CMiller

MARINE

Issued 200 PM CDT Thu Jun 4 2026

Windiest conditions will be today ahead of the front with winds gusting into the 20-25kt range, which will help bump up waves into the 6-8 ft range along the western shoreline before the winds weaken into tonight and Friday. Winds will generally be on the weaker side through the rest of the weekend before the next system moves into the western Great Lakes region early next week.

Halbach

MKX WATCHES/WARNINGS/ADVISORIES

WI...Beach Hazards Statement...WIZ052 until 10 PM Thursday.

LM...Small Craft Advisory...LMZ643 until 10 PM Thursday.