textproduct: Milwaukee/Sullivan

KEY MESSAGES

- Thunderstorms will move across the area this evening posing a risk of hail to the size of quarters, wind gusts to 60mph and perhaps a tornado or two. This activity has moved into southwestern WI and should exit to the east by 11 PM. Areas along the WI/IL border and southeastern WI have the best chances to see a severe storm.

- Heavy rainfall this evening into the overnight hours will maintain a risk for flash flooding into Thursday morning. A Flood Watch remains in effect for all of southern Wisconsin.

- Another round of heavy rainfall, flooding, and severe thunderstorms is expected Friday afternoon into early Saturday morning.

UPDATE

Issued 654 PM CDT Wed Apr 15 2026

A messy mesoscale setup this evening as showers and thunderstorms continue to expand across the region.

Airmass recovery has been slow, but good enough to slip into southern WI, mainly along/south of I-94 corridor. Best dewpoints are along/south of the state line and a few supercells have developed over the past hour or so. Closely monitoring the behavior of these storms as they approach and cross the state line, where one of a few nebulous boundaries reside. The circulation with the supercell just south of Green county has maintained its character as it has crossed the state line, which gives at least some indication that there is a boundary in far southern WI.

For much of the mid/late afternoon, we have observed scattered to numerous showers and storms north of the boundary, which has maintained low 60s dewpoints, but have kept temperatures largely in the low/mid 60s, with the exception of far southeastern WI where temperatures have poked into the 70s. A slightly better thermo environment in far southeastern WI is worth noting as we could see an uptick in intensity as activity moves to the east.

Unlike the past few days, this set up is a bit more uncertain and subtle mesoscale changes will be the focus to learn if storms are slightly elevated or becoming more rooted to the surface, which will open the door to an increased wind potential, along with the risk for a tornado or two.

Heading into the overnight hours, we will remain moist and as the shortwave moves into the region additional areas/bands of showers and embedded storms will linger.

Gagan

SHORT TERM

Issued 335 PM CDT Wed Apr 15 2026

Tonight through Thursday night:

More thunderstorms are possible this evening as return flow is expected to advect appreciable SBCAPE from 1000 to 1500 J/kg into southwest WI and up to the WI/IL border. Storms tonight may be a bit weaker than yesterday given skinnier CAPE profiles, but low level instability, effective shear around 40 knots, and some curvature in the hodographs will support another round of gusty winds and hail. An isolated tornado can't be ruled out along the WI/IL border given the low level turning in the hodographs and low level instability, provided a low-topped supercell forms in the environment this afternoon.

Storms will quickly grow upscale after sunset, leading to more widespread rain. Training thunderstorms may lead to more flash flooding tonight given the wealth of rain we've had this week. A Flood Watch is in effect from 4pm this afternoon to 7am Thursday for the expected rainfall tonight. A widespread 1 to 2 inches may fall, with locally higher amounts possible where any thunderstorms track.

Storms largely move offshore tonight around midnight, with more scattered rain possible between midnight and 7am. Rain should then largely taper off Thursday morning, with dry conditions Thursday afternoon. A weak surface ridge will then move overhead Thursday night.

CMiller

LONG TERM

Issued 335 PM CDT Wed Apr 15 2026

Friday through Wednesday:

A strong cold front is expected to move through Friday afternoon and evening and is expected to lead to another round of severe weather. At this time the GFS depicts strong warm ahead of the front which will allow dew points in the 60s to return northward. Model soundings depict 40 knots of effective shear amid moderate instability of 2000 J/kg, with low level turning in the hodographs. This would support all modes of severe weather again for the area. At this time the SPC has included southwest and south central Wisconsin in an enhanced risk for severe weather.

The cold front will then come crashing through Friday night into Saturday, and temperatures will dip into upper 40s to low 50s for the weekend. Saturday is expected to be cool and breezy, with breaks in the clouds late in the day. Sunday will feature similar conditions but will be a tad bit sunnier as a high pressure center moves overhead.

Warmth is then expected to return next week Tuesday as a ridge builds over the central United States. The middle of next week then looks active again as a low pressure moves off of the lee of the Rockies.

CMiller

AVIATION

Issued 654 PM CDT Wed Apr 15 2026

Primary concern for this evening is another round of showers and storms. The severe risk is a bit more uncertain, but high enough to be concerned with localized damaging winds and hail. There is a small tornado risk. MVFR to brief IFR visibility is expected with heavy downpours of rain. Lightning risk will be highest this evening as storms move west to east and exit over the lake after 04 UTC. Heading into the overnight hours, showers and a few storms will persist in a scattered fashion, with visibility and ceilings lowering through the MVFR category. Prior to daybreak Thursday will be the best window of opportunity for IFR ceilings and visibility. Conditions will gradually improved during the day Thursday, with clearing expected in the mid to late afternoon.

Gagan

MARINE

Issued 251 PM CDT Wed Apr 15 2026

A stationary front will remain parked over the middle third of the lake this afternoon, slowly sinking south to the southern end of the lake by noon Thursday. A Marine Dense Fog Advisory continues until Thursday morning while this front lingers. Winds will remain southerly south of the front and modestly breezy, while winds north of the front will remain light and variable to northerly during this time. The front will then clear the lake Thursday afternoon and northerly winds will prevail over whole lake. Winds will become light and variable briefly Thursday night as a weak ridge passes over the lake, with winds then becoming southerly and breezy Friday ahead of low pressure of 29.6 inches approaching from the west. Gusty northwest winds then return following a cold front Friday night.

Additional thunderstorms are forecast over the southern third of Lake Michigan this evening into tonight. A few storms could be severe with large hail being the primary concern. Additional storms are possible Friday into Saturday, with a few stronger storms possible.

CMiller

MKX WATCHES/WARNINGS/ADVISORIES

WI...Flood Watch...WIZ046-WIZ047-WIZ051-WIZ052-WIZ056-WIZ057-WIZ058- WIZ059-WIZ060-WIZ062-WIZ063-WIZ064-WIZ065-WIZ066-WIZ067- WIZ068-WIZ069-WIZ070-WIZ071-WIZ072 until 7 AM Thursday.

LM...Dense Fog Advisory...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563- LMZ565-LMZ567-LMZ643-LMZ644-LMZ645-LMZ646-LMZ669-LMZ671- LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-LMZ870-LMZ872-LMZ874- LMZ876-LMZ878 until 7 AM Thursday.