textproduct: Milwaukee/Sullivan

KEY MESSAGES

- Periods of showers and storms (60-90 percent chance) expected late this evening through tonight. There is a Marginal Risk for severe storms mainly for damaging winds. Can't rule out isolated large hail or a brief spin up across southwestern Wisconsin.

- Dry weather with highs in the 60s this weekend; cooler by Lake Michigan due to light easterly winds.

- Showers and thunderstorms return late Sunday night through Monday night.

UPDATE

Issued 710 AM CDT Thu Apr 23 2026

No major changes to the going forecast. The latest guidance from CAMs indicates the ~7-11 PM window of scattered thunderstorm activity towards southwestern WI remains on track, followed by additional thunderstorms congealing into a line and sweeping eastward across the entire region through tonight. The best potential for severe weather remains from Madison westward. Central and southwestern WI have the highest potential / expected amounts for rainfall tonight due to the potential for 2 rounds of convection: the scattered activity this evening and the line of thunderstorms later tonight. Areas further east may only observe the fast-moving line of storms late tonight, resulting in lower rain totals.

Sheppard

SHORT TERM

Issued 1202 AM CDT Wed Apr 22 2026

Tonight through Friday:

An upper level trough is out over the Northern Plains and south central Canada tonight. As this upper level cyclogenesis stays near stationary, a shortwave trough will advect northeast out of the Central Plains toward Wisconsin this evening. until the shortwave begins to move toward the state party cloudy to mostly clear skies with above normal temperatures are expected today. Breezy south winds will develop this afternoon as temperatures start to climb.

As the shortwave moves through, a cold front will move southeast down the state. There is a 60-90% chance for a scattered to isolated line of rain and storms to move through late this evening into Friday morning. This line of storms ahead of the cold front will initially be more persistent/continuous. As this line moves east overtime it will be moving into a slightly less favorable environment which will result in the scattered nature. This weakening trend is represented well in all the CAMS. This is in part due to the weak effective shear which will struggle to remain around 20-30 knots by early Friday morning. Western and southwestern Wisconsin will be in a far better environment for strong to severe storms with damaging winds being the primary threat. Can't rule out the briefing tor or hail until the storms become more scattered and isolated. The main hazard/concern will quickly transition to only damaging winds by early Friday morning for eastern Wisconsin.

In addition to the severe thunderstorm potential this evening into Friday morning. There will be a concern for flooding. Given the antecedent conditions we already have of a very wet environment, any rainfall that gets near an inch will potentially cause problems. Many low lying areas and rivers already out of their banks may see little impacts. However urban and small stream concerns will be the primary threat with their quicker responses to more incoming water. This system should be fairly progressive, but can rule out an inch with locally higher amounts toward two inches for southwestern Wisconsin. The last thing worth mentioning with this system, is the severe potential will increase if storms move through earlier than anticipated. The later start time with the loss of some of the diurnal instability and better shear is the main reason for the scattered nature of the line. So the later the better if you are looking to avoid strong storms.

Patterson

LONG TERM

Issued 1202 AM CDT Wed Apr 22 2026

Friday night through Tuesday:

The upper level low across the northern plains and south central Canada will continue to spin over that region through the weekend. Behind the cold front from Friday, a sfc high pressure system will move through Wisconsin Saturday and exit to the east Sunday morning. With the upper level cyclogenesis out to our west and sfc high pressure conditions will remain dry with light winds through the weekend. Until the sfc high moves east of the state winds will remain predominately northerly. Winds will then shift to easterly then southeasterly Sunday as the high exits and the upper level trough advances east toward the Great Lakes Region.

This trough (in northern Plains) and a shortwave out of the Rocky Mountain west will advance toward the Great Lakes Region bringing the next chance for rain and storms Monday. Confidence in rain chances are high around 60-80%, but some uncertainty still remains in exact timing of the rain. This is largely in part due to how fast the shortwave and upper level trough advance east into Wisconsin. You can see the time discrepancies easily in the deterministic, but it also shows up in the ensembles and cluster analysis. For the cluster analysis you can see that the upper level trough out of the Plains has a persistent dipole pattern. Supports and highlight the uncertainty in the position and timing of the trough.

Not anticipating anything more than a few rumbles of thunder for Monday. The features to keep an eye on will be the track of the Low and if the warm front can make it far enough north to make conditions unstable. Guidance generally tries to keep the state north of the warm front which keeps the better conditions for strong storms to our south. PWATS will also increase out ahead of this system with values around 1 to 1.25 possible. With how saturated the ground is already this spring it wont take a whole lot of extra rain to potentially cause some concerns. The current expectations are for widespread values around an inch. So given the uncertainty in the timing and position of the trough this will be a time to keep an eye on the weather.

Beyond Monday, low chances for rain look to linger (10-20%). Don'tanticipate this to be another multi day rain event like the week prior, but that slow moving upper level trough that brought us rain on Monday will be slowly spinning across the Great Lakes through mid week. Any additional shortwave troughs or presence of an upper level jet could create just enough lift to get sporadic light rain. Given that guidance is all over the place on whether or not to be dry which is why chances are low.

Patterson

AVIATION

Issued 710 AM CDT Thu Apr 23 2026

Dry weather and VFR this morning and afternoon, with accelerating south winds. A southeasterly lake breeze is expected to progress ~10-15 miles inland through this afternoon, and the remnants of it may sweep further westward into this evening.

From roughly 7-11 PM CDT, scattered thunderstorms expected to stray into southwestern WI, some could become strong with gusty winds and isolated large hail. Additional showers and thunderstorms then congeal into a line and progress eastward across the entire region through tonight (timing reflected in TAFs). Best potential for strong / severe storms is in the evening (Madison and points westward), with a weakening trend expected as storms track east. Cloud ceilings might decline to MVFR / Fuel-Alt MVFR levels in the event of continued rainshowers late tonight, but should gradually lift post-dawn Friday morning if applicable.

Sheppard

MARINE

Issued 1202 AM CDT Wed Apr 22 2026

Winds will veer southeast tonight and accelerate Thursday afternoon becoming breezy through Friday morning as 29.2 inch low pressure develops over the northern Great Plains. This low pressure system will slowly track east toward the central portion of the Lake Friday night. Some 30 kt easterly winds may occur over the northern tip of the lake Thursday night and Friday.

A Small Craft Advisory may be needed for nearshore zones north of Port Washington due to building waves. The persistent southeast winds early Friday morning through Friday afternoon should cause waves to build to around 4-6 feet.

The low will pull a cold front across Lake Michigan Friday afternoon and evening, resulting in a breezy north-northwest wind shift. Showers and thunderstorms are expected late Thursday night through Friday, both ahead of and along the front. Severe weather is not anticipated at this time.

Northerly winds will continue through the weekend across Lake Michigan. 29.4 inch low pressure is forecast to track northeastward from the central Great Plains (Sunday night) near or over Lake Michigan (Monday night), with gusty east to southeast winds ahead of its arrival and gusty west or northwest winds behind it (into Tuesday). Not seeing widespread gale potential with this system, though trends will be monitored.

Patterson

MKX WATCHES/WARNINGS/ADVISORIES

WI...None. LM...Small Craft Advisory...LMZ643...4 PM Thursday to 1 PM Friday.