textproduct: Milwaukee/Sullivan

KEY MESSAGES

- Strong to severe storms are still expected late this evening into tonight. All severe hazards possible as well as flash flooding.

- Heavy rain this evening and tonight with the storms resulting in localized higher rainfall exceeding 1-3 inches. Thus a Flood Watch is in effect for counties north of I-94 tonight. Also expected rises on area rivers and cresting above flooding stage with the additional rainfall.

- Additional windows for heavy rainfall, flooding, and thunderstorms Tuesday and Wednesday and again later this week.

UPDATE

Issued 809 PM CDT Mon Apr 13 2026

Tonight:

Well organized 925-700 mb warm, moist advection and frontogenesis is supporting severe convection from north central IA and srn MN ewd across central WI. The sly 925-850 mb jet of 40-50 kt will actually increase MLCAPE to 1500-2000 J/KG across all of srn WI this evening ahead of the sfc low that will track from wrn IA to ne IA and se MN by 06Z. CAMs suggest the developing MCS north of La Crosse will move esewd across central WI, while another MCS will form across se MN into sw WI. The 2nd MCS will then track to the right of the mean wind (esewd around 35-40 kt) across much of srn WI. 0-3km shear is 250 degrees around 40 kts and oriented mostly parallel to the expected MCS, but any short north to south line segments would have the potential for QLCS tornadoes. Overall though the main threat is damaging winds. 05-06Z is a good estimate from Fond du Lac to Madison then 07-08Z into the MKE metro area.

Gehring

SHORT TERM

Issued 234 PM CDT Mon Apr 13 2026

Tonight through Wednesday:

Continue to see a very active spring pattern today through Wednesday across southern WI. Strong to severe thunderstorm environment will set up across the area each day varying in location and strength. Will also see heavy rainfall associated with this activity and widespread 1-3 inches possible through the middle of the week, but localized higher rainfall greater than forecast will be possible contributing to flooding impacts. First opportunity for severe and flooding potential will be later today/tonight. Will be another window on Tuesday, which has the better potential for more widespread severe activity over the CWA. Then another window will occur on Wednesday, but will be a bit more uncertain as it depends on what happen today and tomorrow.

Rest of this Afternoon:

MCV has stayed south more into IL and produced a couple perky thunderstorms. However, the cap is holding across southern WI this afternoon and anything that is trying grow upscale is not making it at this time. Will continue to monitor, but the better chances for development will be later this evening.

This Evening into Tonight:

Environment still looking primed for convection across central WI with a warm front strewn across the central part of the state as a surface low over NE lifts eastward. In the warm sector south of the main boundary over southern WI seeing SBCAPE exceeding 1000 J/kg and looking to increase toward 1500 J/kg or more through the remainder of afternoon. Paired steep lapse rates around 7-8C/km, dewpoints already in the 60s, and deep layer shear +45kt all will support development through the evening.

The bulk of the severe and flooding activity is looking to develop early this evening through tonight generally along and around the warm front boundary toward the northern half of the CWA (generally north of I-94) as the nose of 40-55kt LLJ noses into WI. Still looking to see a few discrete development along the warm front back in west central WI early this evening where the instability and deep layer shear align with the LLJ. All severe hazards will be possible for discrete development south of the warm front and cannot rule a tornado or two as 0-1km SRH increased to around 200 m2/s2. Might see a few discrete sneak into our northwest, but majority of it looks to remain just outside our CWA. However given the easterly flow parallel to the frontal boundary expect to see this activity gradually merge and cluster more into a linear structure through the evening. This will transition the severe threat more toward wind and flooding. The 12z CAMs continue to trend toward a more southern shift in this activity and looking to impact our northern tier of counties through tonight. While damaging winds will be the primary severe threat, the convection training over the same area and producing locally higher amounts exceeding 1-3 inches over saturated soils may leading to localized flash flooding as well as rises on area rivers. Thus have issued a Flood Watch for the areas with the greatest concerns tonight.

Expect this cluster to works its way along the boundary overnight with a bulk of the models having it move off and weaken after midnight through early Tuesday morning.

Tuesday- Tuesday Night:

Another window for severe weather expected for Tuesday. Overall looks to be a bit better set up for southern WI as the front from today's activity is progged to be draped across our area. The main question will be where will the boundary set up as depending which side of the boundary you are on will dictate the severe impacts. We are beginning to see a trend with the frontal boundary bisecting our CWA on the global models as well as on the 12z HREF. If this continues, looking at the better severe potential to be favored toward the southern portion of the CWA. Wherever the front sets up, expect areas along and north of the warm front to be more susceptible to large hail threat as instability will be more elevated north of the surface boundary. Looking at MUCAPE between 1000-2000 J/kg along and north of the boundary paired with the +40kt deep layer shear. While areas along and south of the boundary will be capable of producing more damaging winds and cannot rule out even a few tornadoes in addition to hail. More favorable surface based instability with +1500 J/kg of SBCAPE aligning with the deep layer shear in the warm sector. CAMs also are pinging on increasing low-level SRH exceeding 150-200 m2/s2 supportive of a tornado or two.

Storm mode evolution also looks similar to toady as well with convective initiation being more discrete/isolated convection which will be more supportive of supercells and tornado, but CAMs prog this activity to cluster and merge through the evening and thus transitioning to more of a damaging wind and embedded tornado threat.

Lastly given saturate grounds and previous days rainfall any heavier rainfall moving over the same area will be susceptible to flash flooding as well as rises on area river above flood stage.

Again there will be limited upper-level synoptic forcing for Tuesday activity and mainly be driving by low-level WAA, LLJ, warm frontal boundary, as well as localized mesoscale lift from upstream MCV or remnant outflow from today's convection. So will continue to monitor the hi-ress models guidance through this evening to have a better picture of where things set up.

Wednesday: The active spring pattern continues for Wednesday as well. Again still need to see how things pan out Tuesday for exact locations of this activity. However, seeing more upper-level support with the Wednesday round as an upper-level shortwave trough digs across the Plains and lifts over the region. While more favorable upper-level synoptic forcing will be present, the overall surface low track continues to trend over southern WI. This will set up the a frontal boundary more across southern portions of the area, but could see additional shifts. Nevertheless there will be another opportunity for heavy rainfall and severe potential along this system. Will continue to monitor and see if current trends hold or if things shift.

Wagner

LONG TERM

Issued 234 PM CDT Mon Apr 13 2026

Thursday through Monday:

Finally get a bit of a break in this active pattern on Thursday as an upper-level ridge builds into the region. However, this looks to be short lived as an upper-level trough begins to deepen across the northern Plains and gradually lift into the upper Midwest later Friday into Saturday. The associated surface low looks to track up the Upper Mississippi River Valley during this time which will place southern WI in the warm sector. Again looking at environment that will support increased shower and thunderstorm activity. Given the current pattern and track, will need to keep an eye on strong to severe potential for our western portions of the CWA, but the latest trends in the models has this system a bit slower, thus the better environment looks to be further west. Will continue to monitor and see if this trend continues for this late week system.

Behind this late week system, the pattern looks to settle down as the trough pushes into the eastern CONUS while an upper-level ridge looks to build Sunday through the start of next week. Expect mainly drier and mild conditions at this time through this period.

Wagner

AVIATION

Issued 809 PM CDT Mon Apr 13 2026

A line of thunderstorms, potentially severe at times, is expected to drop southeast through southern Wisconsin from roughly 05Z to 09Z tonight. Low level wind shear is likely this evening into tonight ahead of the thunderstorms. Lower ceilings (1500 to 3000 ft) and visibilities (2-5 miles) are anticipated as the line of storms move through.

A few storms may linger towards daybreak early tomorrow, with dry weather likely through the morning hours. Low clouds may take a good chunk of the morning to improve to VFR. Generally south to southwest winds are expected tomorrow, though a few models do show winds may turn onshore tomorrow near the lake by late morning.

Another round of thunderstorms is expected tomorrow by late afternoon or early evening, with the potential for severe storms once again.

DDV

MARINE

Issued 234 PM CDT Mon Apr 13 2026

An active heavy rainfall and thunderstorm pattern is expected across the region this afternoon through Wednesday. Will see frontal boundaries stall across the lake at various location each day with increase thunderstorm activity focused along and around it as well. Overall winds are looking fairly light and may contribute to periods of fog over the open waters. Winds will vary depending on where the fronts set up. Portions of the lake south of the boundaries will see predominantly southerly winds, while more easterly winds are expected north of the boundary. Will see a break in shower and thunderstorm activity for Thursday, but active pattern returns for the end of the week into Saturday.

Wagner

MKX WATCHES/WARNINGS/ADVISORIES

WI...Flood Watch...WIZ046-WIZ047-WIZ051-WIZ052-WIZ056-WIZ057-WIZ058- WIZ059-WIZ060 until 7 AM Tuesday.

LM...Dense Fog Advisory...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565- LMZ567-LMZ868 until 7 AM Tuesday.