textproduct: Milwaukee/Sullivan

KEY MESSAGES

- Highs in the 70s and humid conditions return Sunday and last through much of the new week.

- An active weather pattern returns Sunday and through much of the new week. Severe storms and heavy rain will be possible at times. Rivers are expected to rise with some flooding possible.

UPDATE

Issued 749 PM CDT Sat Apr 11 2026

Low pressure around 994 mb over ern MT will track into ND tnt, while a sly low level jet of 50-60 kt over the ern Great Plains veers into WI. Showers and isold storms will increase in coverage this evening as the ern portion of the low level jet shifts ewd across central and srn WI. Low to mid level thetae advection and frontogenesis, greatest toward central WI, will bring up rain chances to 60-80 percent along and north of a line from MSN to MKE, with lesser chances to the south. Elevated CAPE will remain tall and skinny and mostly under 500 J/KG.

The low pressure area will then track to the arrowhead of MN on Sunday with its warm front quickly shifting nwd over srn WI from 12-15Z Sunday. Some scattered showers and storms will likely continue in the morning as the frontal passage occurs. Despite what may be widespread cloud cover, temps should still reach around 70F within the warm sector with dewpoints possibly reaching 60F. A small shortwave trough and its own sly 50 kt low level jet will approach from the srn Great Plains for the late afternoon and evening. Tall, skinny, surface based CAPE around 500 J/KG will be present with rain chances around 60-90 percent east and south of MSN, lesser chances to the north and west. Severe storm probability will remain very low but cannot completely rule out damaging winds via momentum transfer with any stronger storms.

Gehring

SHORT TERM

Issued 315 PM CDT Sat Apr 11 2026

Tonight through Sunday night: Clouds have increased as WAA/moisture has increased in the midlevels. We will continue to see a few splats of rain this afternoon though given drier low levels this will likely isolated to scattered activity. As we head later into the afternoon, low levels should steadily moisten as the LLJ slides east and rain will become more likely this evening. The warm advection aloft will cause some weak MUCAPE to build to 500 J/kg and some rumbles of thunder may occur early Sunday morning. Overall the moisture will be more consistent throughout the column with no significant dry air to work around but CAMs generally show a scattered nature to activity with better chances building to the northeastern CWA into the evening. Evening chances will be best in the central/northeastern parts of the CWA.

However, based on observations from last night WPC had pointed toward a marginal risk for heavy rain as the outlier ARW model performed best last night in the central US. This CAM (and to a lesser degree the FV3) in particular shows a convective area of storms developing to the west and southwest this afternoon and pushing in during the evening. This shows an extended period of rain showers tonight across southern WI and with PWATs in the 1.25-1.5 in range we could very easily yield some heavy rain concerns overnight. But there remains uncertainty given the differences in the CAMs. It is worth mentioning the 12z HRRR shows an similar feature initially though it pushes through more quickly and does not hold precip through the late night period. Normally, we would rule out the outlier scenario for the most part, but it cannot be ignored given that it best handled the convection in the central US last night and that a few other CAMs have hinted at this possibility, just perhaps not to the same degree. Low lying areas may be susceptible to ponding and minor flooding concerns. Flash flooding is not expected.

Rain may linger into the day Sunday but most CAMs having things largely dry from mid morning through the mid to late afternoon. Then later Sunday into Sunday night we will see a shortwave track through with plenty of moisture and some additional WAA from the LLJ over the area. At first look, this setup appears harmless and looks fairly benign. However, digging deeper, the environment out ahead of the precip associated with the shortwave briefly becomes favorable for severe weather. The global models generally show moist adiabatic soundings but the HREF instability shows perhaps a bit more to tap into (~500J/kg) and with fairly strong shear in the low levels of 30kts or so and deep layer shear around 40kts. This potential is only for the very forefront of precip pushing, which in several models shows isolated to scattered convection pushing in. With non- zero STP and modest supercell composite we cannot rule out any hazard as brief as it may be (~2-4 hour period, 3-7pm). Further into the evening precip will become more widespread with some embedded storms. Periods of moderate rain with heavier rain in storms should be expected and given PWATs across SE half or more of the CWA of 1.25-1.5 in we could see another period of minor flooding concerns, though no flash flooding is expected.

Kuroski

LONG TERM

Issued 315 PM CDT Sat Apr 11 2026

Monday through Saturday:

Into Monday, models have trended largely dry during the day and possibly even through Monday night. A strong inversion aloft with limited forcing over southern WI may limit convective potential at this time. Northern and possibly central parts of WI will see better potential into the late afternoon/early evening for storms given a much weaker inversion, closer to the warm front that may yield better convective potential. Currently southern WI is expected to be south of the warm front, perhaps well south. Global model ensembles somewhat disagree with the EC Ens having the warm front further south, toward central WI, while the GEFS generally has the warm front much further north. In addition, all of the CAMs we have that stretch into Monday afternoon/evening suggest the further north setup with storms largely remaining well to the north, with our CWA remaining dry. Now we cannot rule out the EC setup but it has largely been the outlier for this expected stretch of storm activity for this upcoming week. The EC appears to just be on the slow side and in this case it keeps the surface low much further south and west which then keeps the warm front further south and within our window of risk. Should the EC be correct this would put our CWA in the primary risk area with all hazards possible given the cap gets eroded. If the cap doesn't get eroded, likely nothing happens because there will be limited forcing aloft to get elevated convection. However, assuming the cap erodes all hazard would be possible given high instability environment with plenty of low level and deep layer shear. The most likely timeframe for the cap to erode, should it erode, would be Monday evening, especially if the warm front is not present over the area.

Tuesday still generally appears to bring higher end severe potential but the trend in the models has definitely shifted toward a much more delayed progression of the upper level trough, thus delaying the progression of the surface low. However this has largely just shifted the how and why of the system, only slightly lessening the higher end severe weather concerns. Models do disagree on what is expected to occur across southern WI but general models show a warm front now laying across parts of southern WI with higher instability of 1500+J/kg MLCAPE with decent deep layer shear around 40-50kts with fairly large CWASP. The primary change is that the low level shear appears to be weaker now or at least more uncertain than in previous models. This will be something to monitor as Tuesday approaches. In either case we will likely to be surface based with capping initially but likely eroding by the late afternoon. Plenty of uncertainty still to be worked out as models still not in alignment in a lot of ways but the concern for severe storms persists with all hazards possible.

Wednesday is the day that has changed most drastically, with the delayed trough aloft. This delay in the arrival of the trough actually brings the low through Wednesday afternoon/evening with a highest end severe risk possibly shifting to Wednesday. Still some uncertainty in regard to timing and such but great instability and low to deep layer shear with all hazards being possible. Model differences will certainly still play a role but most of the models show a higher end CWASP over the area indicative of the higher end severe/tornado potential into Wednesday now.

It becomes a bit of a cluster beyond midweek as temperatures and flow remain favorable for warm temperatures, instability and the potential additional impactful systems. Specifically, next Friday (possibly Saturday) may provide us with additional storms and severe weather potential. Next week is shaping up to be a very active week of weather for southern WI.

Kuroski

AVIATION

Issued 749 PM CDT Sat Apr 11 2026

Areas of MVFR Cigs developing tnt from south central WI to central WI as a warm front approaches from the south. Showers are likely at times including isolated storms. The MVFR Cigs will become more widespread Sunday afternoon when additional showers and storms track into se WI from the south. LLWS developing late this evening and lasting a few hours beyond sunrise Sunday via a sly low level jet of 45 kt. Widespread Cigs then falling below 1 kft Sunday evening. LLWS may redevelop over far ern WI as well.

Gehring

MARINE

Issued 315 PM CDT Sat Apr 11 2026

Southeast winds return this afternoon and become gusty tonight as a sharper pressure gradient moves over Lake Michigan as low pressure moves into the northern Great Plains.

Low pressure will shift into the northern Great Plains during the day Sunday as it deepens to near 29.4 inches. The low will quickly shift east toward Lake Superior Sunday night, reaching the southern shores of the Hudson Bay by daybreak Monday morning. Winds will thus increase further across the open waters Sunday through Sunday night. Will be monitoring for gale potential during this time frame, particularly over the northern half of Lake Michigan. As of this forecast update, forecast models continue to suggest possible gales and headlines may be needed in the coming days.

Winds will weaken Monday morning as high pressure of 30.0 inches moves across Ontario. Then, passing low pressure systems will lead to persistently active conditions across Lake Michigan into next week. Will need to monitor thunderstorm development during the Monday- Wednesday time period, as some storms could become strong to severe.

Kuroski

MKX WATCHES/WARNINGS/ADVISORIES

WI...None. LM...Small Craft Advisory...LMZ643-LMZ644-LMZ645-LMZ646...1 AM Sunday to 4 AM Monday.