Area Forecast Discussion

KEY MESSAGES

- Heat indices into the middle to upper 90s across central Wisconsin this afternoon and early evening, where a Heat Advisory is in effect for Wood, Portage, Waupaca, and Waushara counties.

- Strong to severe thunderstorms, and heavy rainfall and urban and small stream flooding, are possible tonight. There are lesser chances for severe storms on Monday. Damaging winds and large hail will be the primary hazards.

- A cold front passing through the region will bring a shift to northerly winds and relief from the high humidity for Tuesday through mid-week, with lower thunderstorm chances until late in the work week.

DISCUSSION

Issued at 225 PM CDT Sun Jul 26 2026

A weak wave of low pressure over sw Ontario will continue ewd across nrn Lake Superior this evening along with an area of weak PVA via vorticity maximums. A little farther to the south, persistent 850-700 mb warm, moist advection will continue across nrn MN to over Lake Superior this afternoon then gradually shift swd into Upper MI and nrn WI this evening via wly 850 mb flow of 25-30 kt.

A tongue of projected RAP MLCAPE is expected to rise to 3000-3500 J/KG from wrn WI to just and west of Duluth by late this afternoon with a high CIN region over ne MN due to cloud cover, then greater instability with less CIN in sw Ontario. The CAMs due initiate convection over ne MN this afternoon within this high CIN region, but it is possible initiation could occur farther to the south where a weak boundary, from the passing sfc trough to the north, will separate light wly winds from sswly winds to its south. It's also possible the showers and scattered storms over nw MN will grow upscale when encountering the higher CAPE environment to its se later this afternoon and evening.

Overall there is much uncertainty on the timing and location this afternoon and early evening, but will count on the aforementioned 850-700 mb warm, moist advection that will gradually shift swd across nrn and central WI through the evening and overnight to bring some clarity to the forecast. MUCAPE should range from 1500-3000 J/KG from east to west across the forecast area tnt, while the mid level cap likely stays over wrn WI. Some CAMs show persistent north to south showers and storms from late evening into Mon AM which agrees well with the persistent warm, moist advection via wly flow aloft. High PWATs of 1.5-1.8 inches will be available and will need to message heavy rain and urban and small stream flooding. The recent dry conditions and the overall uncertainty precludes the issuance of a Flood Watch at this time.

An Enhanced Risk is outlooked for WI but is counting on a mature and severe MCS. Deep layer nwly shear of 50 kt is in place along with the aforementioned values of CAPE and mdt to large DCAPE. However, if more discrete cells or clusters of cells occur instead of a large dominant MCS, large hail and damaging wet microbursts will still remain fairly probable just with lesser coverage. The tornado threat looks low given relatively weak low level wind shear.

For Monday low pressure will track from east central MN across central or srn WI, while a shortwave trough tracks from sw Ontario into the nrn Great Lakes. Scattered showers and storms may still be ongoing Mon AM for the overnight hours, but should mostly dissipate by late morning. New shower and storm development is expected but will focus over the ern half of the forecast area. Believe temps will still rebound back into the 80s but there is much uncertainty given the clouds and precipitation. This will also affect the potential for severe storms which does look a bit lower at this time.

Afterward, this low pressure area and upper wave will occlude and remain over portions of the Mid Atlantic States and New England for Wed and the remainder of the week. This maintains nwly flow aloft for the wrn Great Lakes with a sfc ridge residing over the area for Tue nt-Thu. Shortwave troughs in the flow aloft will then bring 40-50 percent chances for showers and storms Thu nt-Sat. High temps in the lower to middle 80s are expected for much of this period.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 218 PM CDT Sun Jul 26 2026

for 18Z TAF Issuance Issued at 105 PM CDT Sun Jul 26 2026

Scattered fair weather cumulus fields will be present during the early afternoon but are expected to diminish shortly as capping and mixing arrive across the area.

The main concern will be the formation of strong to severe thunderstorms this evening, which will dive southeast from the arrowhead of Minnesota into Wisconsin. Maintained the approximate timing of the first wave of convection across the forecast area. Expect low visibility and ceilings with the strongest storms, bringing conditions to IFR. Additionally, severe storms may also include strong wind gusts and large hail. Behind this initial line, additional rain and storms may develop along an axis from northwest to southeast across the region. Amount of additional thunder with the active weather remain uncertain at this time, but will need to watch for any additional stronger storms.

A relatively short period of quieter weather is then possible across the middle part of the day Monday before we again look ahead towards additional storms Monday evening.

KOSH

Scattered to few cumulus clouds are on their way out this morning as skies clear. Strong capping will then keep skies clear into the evening.

The chance of thunderstorms will increase this evening when clusters of storms pass across the region. Maintained the TEMPO group from the previous routine TAF as the timing window has changed little. Once storms develop far to the north across the arrowhead of Minnesota this afternoon, the timing should be able to be narrowed from the 4 hour group currently in the TAF.

Thunderstorms will be capable of producing strong surface wind gusts over 40 knots, LIFR visibilities, and IFR ceilings in the strongest activity.

Additional showers are also likely to follow, which may maintain the lower ceilings across the area through the overnight hours into Monday.

MARINE

Issued at 225 PM CDT Sun Jul 26 2026

Light to modest sly winds this afternoon and evening will shift wly late tnt into Mon AM, then back to southeasterly for Mon afternoon. Nly winds will then develop Mon nt-Tue with waves increasing to 2 to 4 feet. Patchy fog could develop at times into tnt.

GRB WATCHES / WARNINGS / ADVISORIES

WI...Heat Advisory until 9 PM CDT this evening for WIZ035>037-045. MARINE...None.