Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
Issued by NWS Milwaukee/Sullivan, WI
484 FXUS63 KMKX 211904 AFDMKX Area Forecast Discussion National Weather Service Milwaukee/Sullivan WI 204 PM CDT Fri Aug 21 2026 .KEY MESSAGES... - Storm redevelopment (~40-60% chances) ~2-9 PM this afternoon/evening. A few severe storms can`t be ruled out, particularly along & west of I-39. - Scattered thunderstorms ~12-7 PM Saturday mainly in east- central and southeast Wisconsin. An isolated stronger storm with gusty winds or hail can`t be ruled out. - Dry and pleasant conditions Sunday into the beginning of next week. Storm chances return Tuesday evening into Wednesday. && .SHORT TERM... Issued 205 PM CDT Fri Aug 21 2026 This Afternoon and Tonight: Synopsis/Mesoanalysis: Early day showers & storms have largely vacated early this afternoon, though activity is lingering along the state line from Janesville east to Kenosha. Activity laid down a deeper outflow boundary, with satellite and surface obs showing the boundary extending from Rockford, IL to Monroe to Lone Rock. Further north, a warm frontal boundary is apparent from Mauston towards the Rhinelander vicinity. The northern warm front & southern outflow boundary form the eastern bound on an unstable warm sector in place over west-central and southwest Wisconsin. This warm sector will attempt to work toward south-central & southeast Wisconsin through the afternoon, allowing the atmosphere to recover for additional storm development as a cold front approaches from the northwest. Some redeveloping storms will have the potential to be severe, with chances being greatest along & west of I-39 where instability will be greatest. Large hail and damaging winds are the primary hazards, though an isolated tornado can`t be ruled out. Stay weather aware through this evening. Conditions will dry out after midnight as the cold front pushes out of the area. This Afternoon & Evening: Complex set up for re-developing thunderstorms will be in place across southern Wisconsin during the ~2-9 PM time frame as a cold front moves in from the west. Anticipating general thunderstorm potential areawide during this window as the front moves in, with all storms capable of producing brief heavy downpours and cloud to ground lightning. Widespread flooding potential is low given expected faster storm motions. Any strong/severe storms focusing over the more refined portions of the region getting into the surface warm sector/best instability recoveries. Observational and high-res model trends suggest that this will be along & west of I-39, where a brief window of sunshine will precede the encroaching cold front. Borne out in ongoing activity near La Crosse, modest but sufficient effective shear will be supportive for organized activity (both cells & clusters) capable of damaging winds and some large hail. While directional wind shear is marginal, an isolated tornado can`t be ruled out, particularly in discrete cells that interact with any of the surface boundaries. Will be monitoring radar trends closely for any warnings. Stay weather aware this evening, particularly if planning to be outdoors. Quigley && .LONG TERM... Issued 205 PM CDT Fri Aug 21 2026 Saturday through Friday: Synopsis: Back side of a passing mid-level wave will linger across the western Great Lakes on Saturday, combining with lift along a back door cold front/lake breeze to support scattered thunderstorm development over mainly east-central & southeast Wisconsin during the afternoon hours. High pressure will move through the western Great Lakes Sunday into the beginning of next week, bringing dry and pleasant conditions Sunday through Tuesday. The next upper disturbance is forecast to swing through the region Tuesday evening into Wednesday, bringing the next chances for showers and thunderstorms. Lingering timing uncertainties of the upper level wave & affiliated surface boundaries make the specifics of any strong/severe storm potential unclear at this time, with trends being monitored in coming forecasts. High pressure will build back into the area by Thursday, resulting in quieter conditions. Saturday: Anticipating diurnal thundershower development between ~12- 7 PM as a combination of warming surface temperatures and cool temperatures aloft lead to modest destabilization. Current expectation is for highest precip chances to focus in east-central & southeast Wisconsin, where lift from a backdoor cold front/lake breeze will provide a focus for convective initiation. Forecast soundings point toward weaker effective shear & thus a less organized storm mode relative to today, but can`t entirely rule out an isolated stronger storm with gusty winds or small hail in locations benefiting from full sunshine through the morning/early afternoon hours. Will be monitoring trends. Quigley && .AVIATION... Issued 205 PM CDT Fri Aug 21 2026 Mixture of flight categories prevails early this afternoon behind earlier SHRA & TSRA. Have accounted for current trends in the near- term forecasts at all terminals, with the general expectation for CIGs to lift while winds turn south-southwesterly as the afternoon progresses. Continue to monitor for additional SHRA & TSRA development later in the afternoon as a cold front approaches from the northwest. Development of precip will be heavily dependent on atmospheric recovery in the wake of morning activity, with the eastern extent of better recovery in question as of this forecast. Have thus trended TSRA mentions based on relative confidence from west to east in the 18Z update. Have inserted TEMPO groups at MSN and JVL, where confidence in recovery is higher, while maintaining existing PROB30 groups further east. Will continue to monitor radar trends this afternoon & refine where necessary. Precip chances will diminish by mid-late evening as the approaching cold front clears to the southeast of the region. Quigley && .MARINE... Issued 205 PM CDT Fri Aug 21 2026 South to southwest winds will increase today as a low pressure trough of 29.8 inches approaches southern Wisconsin from the Minnesota Arrowhead. Ongoing thunderstorms over the far southern open waters will vacate this afternoon, with more storm development possible into this evening. A few storms could be strong with gusty winds, and hail. The aforementioned trough will cross Lake Michigan from north to south tonight and bring a wind shift to the northwest. Then look for gusty northerly winds to develop along a cold front that will track from north to south down Lake Michigan Saturday evening. A few thunderstorms are possible along this front. Northerly winds will persist through Sunday as low pressure around 29.6 inches tracks from Lower Michigan to Ontario. Variable winds are expected for Monday and Tuesday as high pressure of 30.1 inches crosses the Upper Great Lakes. Widespread/prolonged Small Craft Advisory conditions aren`t expected through the period in nearshore zones. Will be monitoring for a brief period of advisory conditions next Tuesday, though confidence on the eventual need for headlines is low at this time. Thunderstorms currently moving through the region will clear out by early afternoon, with additional storm development occurring along a cold front this evening. A few of these storms could be strong with gusty winds and hail. Quigley && .MKX WATCHES/WARNINGS/ADVISORIES... WI...None. LM...None. && $$ Visit us at weather.gov/milwaukee Follow us on Facebook, X, and YouTube at: www.facebook.com/NWSMilwaukee www.x.com/NWSMilwaukee www.youtube.com/NWSMilwaukee