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 tornado across southwestern Wisconsin.

- Showers are expected to redevelop on Friday especially over the ern half of WI. Isolated storms still possible.

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

- Widespread showers (80-90 percent chance) and isolated thunderstorms return late Sunday night through Monday night. Chances are fairly high for an inch of rainfall.

UPDATE

Issued 705 PM CDT Thu Apr 23 2026

There are two different areas to watch here this evening as the cold front in western MN and IA moves east toward Wisconsin. Within the warm sector in eastern IA and western IL there are scattered storms developing that are moving north northeast. These storms are riding the line of better instability and shear that remains just to our west (SBCAPE ~ 2000 J/kg and ~30 kts respectively). These showers out ahead in the warm sector could produce some heavy rain and maybe some damaging winds and hail if they can get tall enough. As things stand now its unlikely that these storms will cause much of an issue. While the environment is overall much weaker across southern Wisconsin these scattered storms will work over what we do have if they move far enough east.

The main area to watch will be the north to south line of storms stretching from southern MN into KS. This line is also expected to weaken with time as it moves through southern WI. MUCAPE is generously around 1000 J/kg and SBCAPE isnt expected to improve overtime. The good lapse rates that we have now to support hail growth will also fall off as the sun begins to set. Shear should remain around 20-30 kts through the event which will support the potential for damaging winds. Given that this line should weaken, it will become more scattered/broken with time. This will leave storms on a more multi to single cell setup so any wind damage should become scattered to isolated as storms move into eastern Wisconsin tonight.

Heading into tonight there are no major changes on the flooding potential. As moisture rises across the forecast area tonight, heavy rain will become increasingly more common. The main impacts still remain along the order of urban and small stream type impacts, but any storms that train a bit or slow their forward progression will be the ones to keep an eye on. Overall western WI can expect around 0.25-1 inch of rain, while areas further east trend lower due to the scattered nature of the storms. Can't rule out locally higher up to 2 inches for western Wisconsin, but storms motion needs to be slow or training needs to occur to actualized that.

Strong to severe storms chances will diminish tonight leaving heavy rain and lightning as the primary threats once we reach the early morning hours (roughly 3 to 6 AM). Rain may continue to linger across eastern Wisconsin through the morning commute.

Patterson

SHORT TERM

Issued 223 PM CDT Thu Apr 23 2026

Tonight through Friday night:

Will be watching for convective development over ern IA later this afternoon, where an outflow boundary resides, CAPE builds, and increasing PVA primes the environment. At least scattered storm development is likely and these would be the storms to track newd into sw and south central WI as early as early evening. Although effective shear will be a bit weak at 20 kts, MLCAPE around 1000 J/KG and steep mid level lapse rates could still support a severe storm.

Otherwise the main MCS, tied to the current storms over wrn IA, will track into south central WI after 03Z-04Z. MUCAPE around 1000 J/KG may still be present over the region with swly 0-3km shear at 30kts. With much of the wind shear located in the low levels, bows and surges along the convective line will support isold damaging winds. Mesovortex generation will be possible with any bows or surges toward the north. Although mid level lapse will initially be steep, a moistening troposphere with PWATs rising to 1.3 inches will reduce the lapse rates by late evening and aid in preventing greater coverage of severe winds. Most CAMS then support the diminishing stage of the MCS for ern WI as the outflow out runs the line, but still expect at least 60 percent chances for showers and isolated storms all the way to Lake MI. Urban and small stream flooding will remain possible over south central WI where 2-3 rounds of storms are possible. Localized 2 inch rainfall amounts possible.

The models have sped up the cold front for Fri with higher confidence in the front reaching Lake MI by 18Z, but there are some indications of post frontal rain via mid level frontogenesis. Thus will maintain fairly high PoPs of 50-70 percent, but lesser west of Madison. Showers and isold storms will decrease from west to east from the late morning into the early afternoon. With impressive subsidence and drying afterward, sunshine expected by early afternoon over south central WI and late afternoon over ern WI. High temps in the middle to upper 60s are forecast. Areas of fog will continue over the lake into tonight and Friday due to relatively mild and moist air flowing over the cold lake surface. Modest south to southeast winds developing this afternoon and lasting into Friday as a trough of low pressure and cold front approaches from the Great Plains. However, breezy easterly winds are expected over the northern tip of the lake this afternoon into Friday, as the warm front will stall before reaching said location.

The low will pull a cold front across Lake Michigan Friday afternoon and evening, resulting in modest northwest to north winds. Showers and thunderstorms are expected late tonight through Friday, both ahead of and along the front. Severe weather is not anticipated at this time.

Light north winds on Saturday will then become easterly Saturday night and Sunday before increasing into Monday. 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 winds behind it (into Tuesday). Not seeing widespread gale potential with this system, though trends will be monitored. Gehring

LONG TERM

Issued 223 PM CDT Thu Apr 23 2026

Friday night through Thursday:

A weak high pressure area will then pass on Sat followed by increasing sely winds and warm advection for Sunday ahead of cyclogenesis over the central Great Plains. The low pressure area and associated shortwave trough is then expected to lift newd into WI Mon and Mon nt, with another round (70-90 percent) of showers and storms. At this time, widespread rainfall totals of an inch are reasonable. Relatively quiet weather will then return Tue-Thu via wnwly flow aloft. Temps around normal are forecast with slight chances for showers.

Gehring

AVIATION

Issued 705 PM CDT Thu Apr 23 2026

VFR to IFR conditions are possible through the period. Upper level clouds are slowly building in from the west this evening as a cold front approaches from western IA and MN. As rain and thunderstorms move in late this evening into tonight, ceilings are expected to fall to around 1-3 kft. The lower ceilings are expected to be with any of the rain that moves through. As the rain becomes more scattered to isolated overnight, ceilings could jump around a bit between IFR to MVFR until roughly 9Z. Then MVFR cigs should spread across southern Wisconsin and remain through the rest of the morning. Visibilities around 2-4 SM will also be possible through the overnight hours with any storm/rain. Heavy rain will be possible which could drop visibilites a bit lower at times (about 1 SM). Rain showers will linger into Friday morning as the cold front exits to the east. Ceilings will improve back to VFR from west to east through he morning and afternoon hours.

Breezy south to southeast winds this evening will weaken slightly tonight and loose their gusts. The cold front will pass early Friday morning into early Friday afternoon turning winds to the northwest. By Friday night, the winds will weak further and become northerly winds will continue to slowly turn becoming easterly by Saturday night.

Patterson

MARINE

Issued 223 PM CDT Thu Apr 23 2026

Areas of fog will continue over the lake into tonight and Friday due to relatively mild and moist air flowing over the cold lake surface. Modest south to southeast winds developing this afternoon and lasting into Friday as a trough of low pressure and cold front approaches from the Great Plains. However, breezy easterly winds are expected over the northern tip of the lake this afternoon into Friday, as the warm front will stall before reaching said location.

The low will pull a cold front across Lake Michigan Friday afternoon and evening, resulting in modest northwest to north winds. Showers and thunderstorms are expected late tonight through Friday, both ahead of and along the front. Severe weather is not anticipated at this time.

Light north winds on Saturday will then become easterly Saturday night and Sunday before increasing into Monday. 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 winds behind it (into Tuesday). Not seeing widespread gale potential with this system, though trends will be monitored.

A Small Craft Advisory remains in effect late this afternoon into early Friday afternoon north of Port Washington for building waves.

Gehring

MKX WATCHES/WARNINGS/ADVISORIES

WI...None. LM...Small Craft Advisory...LMZ643 until 1 PM Friday.