Milwaukee/Sullivan, Wisconsin

• Brief period of rain moving in from the southwest through the rest of this afternoon & early evening. Lightning is not expected in any activity.
• Unsettled weather pattern will impact the area Monday through Wednesday, bringing widespread rainfall and a few thunderstorms.
• Unsettled weather may continue into the end of the week before dry conditions take hold next weekend.

Issued 205 PM CDT Sat Oct 31 2026

This Afternoon through Sunday Night

Synopsis/Mesoanalysis: High pressure is centered near Lake Erie this afternoon, resulting in generally southeast winds across southern Wisconsin. A weak area of low pressure is centered over northeast Wyoming, with a diffuse warm front extending east-southeast from the low through South Dakota into southwest Wisconsin. Surface temperatures differences are ill-defined across the Wisconsin segment of the boundary, though residual warm advection and frontogenesis near 925 mb have provided sufficient forcing for rain currently extending from Platteville toward Janesville. Expect this activity to attempt to work northeast through the remainder of the afternoon and into the first half of the evening. Currently centered over the Kansas City vicinity, shortwave troughing will shift toward southern Lake Michigan tonight. Affiliated lift from the wave may trigger an isolated shower or sprinkle in far southeast Wisconsin, with other locations staying dry. Aforementioned areas of surface high and low pressure will linger over the same vicinities on Sunday, with sunnier skies allowing for warmer high temperatures in the presence of southeasterly surface flow.

Rest Of This Afternoon: Anticipating that rain currently ongoing from Janesville to Platteville will continue to migrate northeast along a band of 925 mb warm advection and frontogenesis. Despite larger dew point depressions in the near-surface layer regionally, forcing within the WAA-FGEN band has provided sufficient lift to overcome evaporation/produce a brief period of rain. Have adjusted near-term precip probs to account for expectations. Accumulations will remain light (~0.1" or less), with an absence of instability pointing toward minimal thunder/lightning potential.

Quigley

Issued 205 PM CDT Sat Oct 31 2026

Monday through Saturday

Synopsis: A elongated area of upper troughing will progress into central portions of the continent Monday through the middle of the week, slowly dragging an attendant surface front eastward in the process. The trough and surface front will pull close enough to influence southern Wisconsin`s weather Monday afternoon into at least Tuesday night, when widespread rain and a few thunderstorms are possible. Precise pattern evolution becomes considerably more uncertain from mid-week onward, with a multitude of potential solutions regarding the progression & fate of the early week trough and surface front in-play. With some potential for one or both of the features to linger in the vicinity of southern Wisconsin, conditional periods of rain chances continue through the end of next week. Temperatures are expected to remain either at or above early November normals through the duration of the period.

Monday afternoon through Tuesday: The most confident window of the long term forecast period opens as a coupling of low & mid-upper synoptic forcing arrive into the area, driving widespread rain potential. Expecting precip to begin Monday afternoon & evening as large scale warm advection increases regionally, with rain potential extending into Tuesday as the primary surface front & upper wave encroach from the west. Available medium-range forecast soundings hint at some weak MUCAPE through this portion of the period, so can`t entirely rule out a few thunderstorms mixing in with the widespread rainfall. Tend to think that projected MUCAPE values will be too meager to support any stronger thunderstorms, but will be monitoring trends. Presence of embedded convection within an environment characterized by 1.3"+ precipitable water values could, however, lead to some brief heavy downpours in storms. Not anticipating a widespread flooding threat at this time given the isolated & brief nature of any such downpours. Initial probabilities from the NBM point toward 0.25-0.50" rainfall totals areawide, with the potential for locally higher totals to 0.75"+ where any heavier downpours focus.

Wednesday-Friday: Off/on, conditional rain chances remain forecast with some potential for the early week surface front and/or upper trough to linger regionally. Whether one/both of these features actually do linger will depend on 1) the phasing of northern and southern perturbations embedded within the broader area of longwave troughing and 2) the subsequent impacts on the strength of the surface front. If upper phasing occurs, height falls will linger over the western Great Lakes through the end of the week, combining with the remains of the surface front to support continued off/on rain chances. If phasing doesn`t occur, a tendency toward height rises will become favored, combining with a decaying surface front to support drier conditions. Neither deterministic nor ensemble-based guidance point toward a favored solution at the moment, with trends being monitored for convergence over coming updates. Given the prevailing uncertainty, have maintained precip probabilities from the NBM in the afternoon update & will plan to refine as this portion of the period draws closer.

Quigley

Issued 205 PM CDT Sat Oct 31 2026

VFR flight categories prevail through the period at all terminals. Radar imagery shows an area of -SHRA approaching the Wisconsin-Illinois state line early this afternoon, with activity attempting to work its way northeastward into early evening. Have inserted prevailing groups at MSN and JVL, where confidence in rain observations is highest given observational and short-term model guidance trends. Whether activity holds together further northeast remains uncertain, so have maintained & refined existing PROB30 groups to better align with observational trends. Will be monitoring radar returns through this afternoon & inserting TEMPO or prevailing groups if necessary. Precip potential should wane this evening at most terminals, but will need to monitor for isolated -SHRA in the vicinity of KENW after midnight. Have withheld any mentions in the 18Z forecast given low forecast confidence and will monitor trends through this evening.

Quigley

Issued 205 PM CDT Sat Oct 31 2026

1032 mb high pressure is centered near Lake Erie this afternoon, resulting in generally east to southeast winds across the open waters of Lake Michigan. The high will drift southeast into the northeastern United States through Sunday, allowing winds to trend southerly across the lake. Low pressure near 1000 mb will develop over eastern Colorado Sunday evening, progressing into the Upper Mississippi River Valley into early Tuesday morning. Winds will steadily become gusty ahead of the approaching low, approaching or exceeding gale force over at least the central third of the lake Tuesday afternoon and evening. Anticipate that headlines will become necessary in later forecasts.

Winds will remain breezy, though likely below gale levels Wednesday and Wednesday night as 1020 mb high pressure slowly builds into the Canadian Great Plains. Said high will move into the western Great Lakes through the second half of next week, allowing for westerly and eventually north winds by next weekend.

A brief period of elevated waves continues through this afternoon in nearshore zones, with a Small Craft Advisory in effect through 10 PM CDT from North Point Light to Sheboygan. A prolonged period of gusty winds and elevated wave heights is then anticipated from Monday through at least Wednesday morning, with a combination of Small Craft Advisories and Gale Warnings becoming necessary in later forecasts. Most likely period for gales will be Tuesday afternoon & evening, with Small Craft Advisory conditions anticipated in the lead up to and following the gale time frame. Conditions will improve Wednesday night into Thursday.

Quigley

WI

None.

LM

Small Craft Advisory...LMZ643-LMZ644 until 10 PM Saturday.