textproduct: Milwaukee/Sullivan

KEY MESSAGES

- Increasing humidity and thunderstorm chances tonight with a 1 out of 5 (Marginal) risk for severe storms. Hail, gusty winds, and lightning will be the main hazards.

- A very humid airmass will return Monday and Monday night ahead of approaching low pressure with widespread showers and scattered thunderstorms forecast.

- Hot and humid conditions expected mid to end of next week with some potential for Heat Advisory conditions late next week.

UPDATE

Issued 658 PM CDT Fri Jun 5 2026

Increasing MUCAPE (~1500 J/kg) over southern Wisconsin this evening will allow for maintenance of a broken line of thunderstorms currently sinking southward through central Wisconsin. Expecting the primary hazards with these storms to be hail and gusty winds. An isolated cell may become strong enough to produce hail up to 1 inch in diameter, primarily in southwestern Wisconsin. Storms will continue southward through early Saturday morning.

MH

SHORT TERM

Issued 157 PM CDT Fri Jun 5 2026

This afternoon through Monday night:

Heavy rainfall has fallen today over sw WI where a Flood Advisory is in effect for Lafayette County. A west to east swath of 3-5 inches of rain has fallen. There is some road flooding in the Cuba City area. Otherwise 1-2 inches has fallen south of I-94. This efficient rainfall is a result of moist adiabatic lapse rates within a high PWAT atmosphere of 1.7 inches. The showers are finally decreasing over sw WI, but will continue to increase over far se WI into the middle afternoon as a shortwave trough slowly moves from ne IL to over Lake MI. Brief heavy rainfall rates are expected.

For this evening into the overnight, another shortwave trough currently over se MN and north central IA will move to central WI for early evening, while a stronger shortwave trough over ern ND moves into ne WI after midnight. At the sfc, a broad area of low pressure will move ewd from MN across the nrn half of WI and the Lake Superior region this evening with just a weak wind shift to wly over srn WI. MUCAPE of 1000-1500 J/KG will be in place tnt with one or two clusters of thunderstorms moving across the nrn half of WI. However, the srn periphery of those storms could drift into central WI and/or isolated to scattered storm development is expected over much of srn WI as well. The CAPE values and mdt effective shear does yield a Marginal Risk of severe storms with large hail and damaging winds the main concern. The chances for showers and storms will then greatly diminish around or just after sunrise with 500 mb height rises expected for the remainder of the day, while sfc ridging builds from Ontario south across Lake MI into Sat nt.

The high will begin to already move ewd on Sunday as a broad upper trough over the central and srn Great Plains slowly lifts toward the Upper MS River Valley or srn Great Lakes for Mon-Mon nt. Abundant moisture with PWATs approaching 2 inches will accompany the upper trough. Widespread showers and scattered storms are currently forecast for Mon-Mon nt, but could start as early as late Sun afternoon or night over sw WI. If the upper trough and moisture plume can directly lift into srn WI, concerns for flooding will increase.

Gehring

LONG TERM

Issued 157 PM CDT Fri Jun 5 2026

Tuesday through Friday:

Latest model guidance is showing that southern Wisconsin will remain on the northwest side of upper ridging Tuesday through the end of next week. This is expected to result in a persistent stretch of warm and humid conditions through this period. Precipitable water values are forecast to be 1.5" to 2.0" per 12Z deterministic models, with dewpoints anywhere from 65 to 75. Above normal high temps in the mid to upper 80s may crack the low 90s at times, with 925 mb temps upwards of 25C expected. Overall though, ECMWF and GFS ensemble probabilities of hitting 90 degrees are only in the 10-25 percent range, so confidence isn't high yet in getting quite that warm.

Given the warm and humid conditions mid to late week next week, plenty of instability is expected each day. Since southern Wisconsin will be on the northwest side of the upper ridge, the door will be open for a couple shortwaves to move through during this period, bringing a chance for showers and storms at times. Additionally, the forecast temps and dewpoints suggest the potential for the heat index to crack 100 degrees at times. The timing of the higher precip chances and hottest temps are still in question though, given uncertainty in the timing of the individual shortwaves, as this forecast period is still a few days out.

DDV

AVIATION

Issued 658 PM CDT Fri Jun 5 2026

Ceilings between 2500 and 3500 ft this evening within some isolated showers. A broken line of thunderstorms will progress southward late tonight into early Saturday morning, bringing ceilings around 2500 ft and the threat of lightning. An isolated strong storm may produce damaging wind and hail generally less than 1 inch in diameter. Storm chances diminish along and south of the I-94 corridor, but potential remains for storms to maintain intensity and progress all the way through the WI/IL border.

Southwesterly winds through much of tonight will shift to become northwesterly as a cold front works its way through Saturday morning. Winds will become light and variable Saturday afternoon into Saturday evening, with an easterly lake breeze expected along Lake Michigan terminals.

MH

MARINE

Issued 157 PM CDT Fri Jun 5 2026

Broad low pressure of 29.6 inches will slowly move across the northern Great Lakes this afternoon and evening. Its weak and decaying cold front will then follow for Saturday afternoon. Thus modest south winds today will shift west to southwest tonight and Saturday morning, followed by light and variable winds Saturday afternoon. During this time, areas of dense fog will be possible due to humid air flowing over the cold lake. Light northeast winds will then prevail Saturday night and Sunday as high pressure around 30.0 inches builds across the region. Looking ahead, the start of next week will bring an additional low pressure system to develop over the Great Plains and approach Lake Michigan with modest southeasterly winds expected.

Gehring

MKX WATCHES/WARNINGS/ADVISORIES

WI...None. LM...Dense Fog Advisory...LMZ643-LMZ644 until 10 PM Friday.

Dense Fog Advisory...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565- LMZ567-LMZ868 until 1 PM Saturday.