textproduct: Milwaukee/Sullivan

KEY MESSAGES

- Scattered thunderstorms this morning into the afternoon. Severe storms are not anticipated, but possibly small hail and gusty winds with the stronger storms.

- More rounds of showers and storms late tonight into Mon then again late Mon night into Tue, but much uncertainty for severe storms given the morning timing of potential MCSs.

- Cool and drier weather then returns for Wed-Thu.

UPDATE

Issued 1020 AM CDT Sun May 17 2026

Now that we are beginning to see the hand that is being dealt, lets break it down:

Remnant decaying complex moving across southern WI this morning bringing showers through late morning and departing early afternoon. While this MCV is moving over a highly stable environment with the onshore flow off of Lake Michigan, have seen parts of this system tap into the elevated instability (MUCAPE ~500-1000 J/kg) and perk up enough to produce a few thunderstorms. As the MCV pushes eastward through the early afternoon, may see additional redevelopment with some daytime heating and beginning to see signs of this back in northeastern IA/southwestern WI. However, still uncertain on if this will become more widespread or if the stable marine layer will win out as it departs. If things are able to recover enough and tap into the elevated environment, then a few isolated strong storms cannot be ruled out now through the early afternoon with some hail possible with the departing MCV, which looks to push east after noon between 18z-20z. While severe potential remains on the lower side at the moment, will need to monitor as MCVs are notorious for creating localized environments that can support healthier/stronger storms right along the feature.

The next area to watch is behind the departing MCV. While the onshore flow and lingering clouds will keep parts of southern WI, mainly north of I-94 in a more cool/stable environment, there is a warm front stalled just south into northern IL. Initial runs of the 12z models are hinting that we see this warm front lift back northward this afternoon bringing warm/moist airmass back into southern WI, generally south of I-94. Accompanying the surface front progression will be increasing instability (SBCAPE of +1500 J/kg) along with lift from low-level WAA as well as a nose of 30-40 kt LLJ. So some of the ingredients for stronger storms may present itself later this afternoon along the warm front, but the questions remains how the morning round of showers, clouds, as well as easterly onshore flow off of Lake Michigan limit the northward advancement of the warm front or if the environment is worked over too much. So for this round of activity will need to see how things lie in the next few hours, but leaning toward the cooler air limiting the threat.

While uncertainty on environment recovery remains in play, especially for southeastern WI, it does have a better chance across southwestern WI where storms and clouds depart sooner. So while we need to monitor for potential development later this afternoon and evening, will also need to keep an eye on how things play out upstream across western IA into the Plains. If we do not see storms develop along the lifting warm front in the afternoon/evening, the environment will be more supportive of overnight storms that develop across the Plains and push into the area overnight into Monday morning. Instability with SBCAPE of +1000 J/kg and meager (30-35 kt) deep layer (0-6km) shear paired with low-level forcing may be enough to maintain the storms strength into our western portions of the CWA. The 12z CAMs continue to show a line of storms developing upstream in IA and pushes east overnight. This would bring more of wind threat to southwestern WI with the line. However there are two camps with the line. One camp with the 12z HRRR, NSSL, and RRFS having the line making to southwestern WI and gusting out as it pushes eastward, likely favoring the warmer solutions winning out while the other camp 12z NAM Nest and ARW weakening the line and/or have it dive further south of the WI/IL border favoring the cooler solutions. At this time temps are under performing and hedging the forecast more toward the cooler solutions, but it also will not take much for the warmer solutions to pan out as well. Either way, the line of showers and storms is expected to move through southern overnight, generally after midnight departing around daybreak Monday with a weakening trend to the east.

Regardless, stay weather aware today as there remains multiple windows for storms now through tonight with potential for strong to severe storms capable of hail and gusty winds as well.

Wagner

SHORT TERM

Issued 1223 AM CDT Sat May 16 2026

Tonight through Tuesday night:

The dry cold front is currently accelerating down Lake MI and will arrive in the Sheboygan area around 1 AM CDT and MKE around 4 AM CDT. Farther to the southwest, a west to east line of slow moving thunderstorms extends from ne IA into sw WI, probably triggered by elevated warm, moist advection. A sswly low level jet of 35-40 kt is expected to develop over ern IA and nose into far srn WI toward 10Z so expect scattered storms to develop over the area. MUCAPE of 1000-1500 J/KG near the IL border will slowly drift nwd during the overnight, but lapse rates will weaken resulting in MUCAPE falling below 500 J/KG. Still expecting small hail within the stronger storms tnt.

Otherwise, more widespread showers and storms are expected from Sun AM into the early to mid afternoon when 850-700 mb warm, moist advection and a MCV moves through the region. The MCV will develop from the severe convection over srn IA and nrn MO tnt and lift newd into srn WI after 12Z. The remnants of the showers and storms from NE to srn IA and nrn MO may accompany the MCV or new development will occur given the aforementioned warm, moist advection. The mid level lapse rates will drop to 5.5-6.0 C/KM during this time so elevated CAPE will remain marginal with perhaps small hail with the stronger storms. The sfc warm front will not reach a line from Madison to Kenosha until late afternoon but temps will quickly warm to near 80F once it passes. High temps toward central WI should only reach into the 60s with 50 and 60s at the Lake MI shoreline.

A wave of low pressure will then track from ern NE to nw WI by 12Z Mon, while a decaying MCS from srn MN and IA may be arriving after 09Z Mon over south central WI. The wave of low pressure will weaken as it tracks newd across Lake Superior into Ontario during the day, but will aid in continued warm, moist advection over srn WI. A MCV may also be present within the decaying MCS, and will forecast 60-70 percent chances for showers and sct storms. The severe storm potential is very uncertain given the morning arrival of showers and storms and there may be a lack of forcing later in the afternoon.

Another wave of low pressure will develop from the central Great Plains to nrn WI by 12Z Tue, while the main shortwave trough tracks from the central Rockies to nw WI. The actual trailing cold front will likely not pass until Tue, but there is some confidence in another round of showers and storms for Mon nt-Tue AM given srn WI remains downstream of areas of new convective initiation and possible MCSs. The potential for severe storms is very uncertain given the morning timing.

Gehring

LONG TERM

Issued 1223 AM CDT Sat May 16 2026

Wednesday through Saturday:

High pressure and a cooler air mass will follow for Wed-Thu with lgt sly winds and warm advection returning late Thu into Sat as the high moves ewd and a shortwave trough approaches from the west. Thus high temps in the 60s for Wed-Thu will return to the 70s well inland from Lake MI for Fri, then 70s over all of srn WI on Sat. A slight chance for showers is forecast Fri nt-Sat.

Gehring

AVIATION

Issued 618 AM CDT Sun May 17 2026

A cluster of thunderstorms is expected to move in from the southwest this morning, with scattered storms then lingering into the afternoon. As the storms move in, ceilings are expected to lower to low VFR to MVFR, with other potential drops in flight category due to vis restriction. Winds will be breezy, out of the east to southeast.

There should be a lull in activity late in the day, with ceilings giving way to SCT to FEW skycon tonight. More thunderstorms may move in from the west around daybreak on Monday.

CMiller

MARINE

Issued 1223 AM CDT Sat May 16 2026

A cold front over central Lake Michigan early this morning will track to far southern Lake Michigan by daybreak. A wind shift to the northeast is expected along with brief gusty winds. The front will then gradually return north as a warm front mainly tonight, with winds veering southerly and becoming gusty. Areas of fog may form later today and evening as the front moves northward. Breezy south winds will then continue into Tuesday followed by a wind shift to the northwest late Tuesday afternoon and evening with the passage of a cold front. High pressure and light and variable winds will then take hold from late Wednesday into Thursday. A Small Craft Advisory may be needed from Sheboygan to Winthrop Harbor for Mon-Tue due to persistent and gusty south winds and high waves.

Gehring

MKX WATCHES/WARNINGS/ADVISORIES

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