NWS Milwaukee Forecast Discussion
000 FXUS63 KMKX 270930 AFDMKX Area Forecast Discussion National Weather Service Milwaukee/Sullivan WI 430 AM CDT Sat Apr 27 2024 .KEY MESSAGES... - Multiple rounds of showers and thunderstorms are expected through the weekend, with storms possibly lingering into early Monday. Locally heavy rainfall will be possible, especially along and south of the I-94 corridor. - A few thunderstorms may be severe during this active pattern. Hail, damaging wind gusts, and isolated tornadoes are all possible, especially late this afternoon into this evening. - Additional chances for showers and storms mid to late week next week. && .SHORT TERM... Issued 415 AM CDT Sat Apr 27 2024 Today through Sunday: Early today: Except for a band of light rainshowers currently passing close to Sauk and Marquette counties, dry weather is expected to prevail until this afternoon, with gusty southwest winds rapidly building after sunrise. The strongest wind gusts are expected near Sheboygan and Fond du Lac counties, upwards of 40 mph. Roughly 30 to 40 mph gusts elsewhere. This afternoon / evening: Storms are expected to develop along a southwest to northeast oriented frontal boundary, perhaps as early as 1 PM or as late as 7 PM today. CAMs currently depict the position of convective initiation as a line from Monroe WI to Sheboygan WI, with roughly one or two counties distance east/west disagreement in positioning. Forecast soundings indicate southwest winds throughout the column, with unidirectional shear, yet impressive helicity integrals. HREF Mean MUCAPE south of the boundary exceeds 2000 j/kg, with a surface-based effective inflow layer. HREF mean STP exceeds 2.0, with some models (esp. the Nam NEST) pushing 3.0. This parameter space would suggest an environment capable of all SVR hazards (hail, damaging winds, and possibly tornados). Localized heavy rainfall is a concern, especially if storms along the front affect the same area multiple times. The best agreement in model QPF is positioned along and south / southwest of the I-94 corridor. Late tonight through Sunday: Instability is progged to decline late tonight. Some models depict a lull in shower / storm activity late tonight, while others depict wider storm coverage with weaker intensity. Severe wx potential does continue into Sunday, but with HREF mean MUCAPE less than 1000 j/kg (even with the compliment of daytime heating), this is looking like the less active day of the two. That said, the positioning of the warm front leaves much in question in the way of instability. Regardless of severe wx potential, localized heavy rainfall seems equally probable on Sunday, with model QPF evenly split between the two rounds of activity. Sheppard && .LONG TERM... Issued 415 AM CDT Sat Apr 27 2024 Sunday night through Friday: Synopsis: The upper trough ejecting into the Northern Plains on Sunday afternoon/the conclusion of the short term period will progress toward the Canadian border Sunday night into early Monday morning. The advancement of the upper wave will support surface low placement along the MN-WI border vicinity by sunrise Monday, with a cold front forecast to be extending southwest into the Central Plains. The upper trough will progress across Lake Superior during the day on Monday, gaining separation from its attendant surface cyclone in the process. This will promote gradual filling of the surface low over northern WI and the Upper Peninsula of MI Monday afternoon, with the associated cold front crossing & ultimately exiting the region during the evening hours. The advancing upper wave & surface front will support additional periods of showers and embedded thunderstorms from Sunday night through Monday afternoon. Westerly surface flow will usher a drier/Canadian air mass into the state Monday night, with winds quickly turning back out of the south from Tuesday into the middle portions of next week. Occurring in response to an upper jet/trough pairing approaching from the Northern Plains, said southerly flow will allow moisture to return to the area on Tuesday afternoon. Additional showers and storms will be possible Tuesday night through Wednesday as a surface low related to the upper trough/jet tracks across Ontario & pulls a cold front across the state. The boundary is likely to stall out somewhere to our south & east during the Thursday/Friday timeframe, with considerable spread in placement evident in current deterministic & ensemble-based guidance. Sunday Night & Monday: Anticipate periods of showers and embedded thunderstorms. While depicting plenty of shear through the column, available forecast soundings show only weak (