Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
Issued by NWS Milwaukee/Sullivan, WI
076 FXUS63 KMKX 312323 AFDMKX Area Forecast Discussion National Weather Service Milwaukee/Sullivan WI 623 PM CDT Mon Aug 31 2026 .KEY MESSAGES... - Heat & humidity continues through midweek. Afternoon heat indices in the low-mid 90s expected each day through Wednesday, with upper 90s to near triple digits possible in areas experiencing more sunshine. Warm temperatures linger into the weekend, with heat index values in the upper 80s to low 90s Thursday through Sunday. - Isolated thunderstorms possible this evening and again Tuesday afternoon and evening. - Areas of fog expected overnight tonight, with potential for patchy dense fog in low lying areas. - Scattered storm chances return late Tuesday night into Wednesday morning, especially for central Wisconsin. Additional scattered storms will occur on and off Wednesday through Friday. && .UPDATE... Issued 625 PM CDT Mon Aug 31 2026 Forecast remains largely on track early this evening. MCV- affiliated lift continues to move across southern Wisconsin, though an absence of surface boundaries & stout EML-affiliated capping are keeping any precipitation widely scattered & of mostly benign intensity. With a synoptic cold front still well north of the area & an outflow boundary from earlier afternoon storms remaining over northern Illinois, anticipating these trends to continue into the second half of the evening across the majority of the area. Current 15-25% precip probs thus appear reasonable, with no intermediate changes needed at this time. While mean westerly steering flow & considerable capping off the surface front should hold activity north of the region, will be monitoring for any closer calls between isolated cold frontal storms & our northern counties through mid-evening. If an isolated storm snuck in, it could produce some small hail or gusty winds. Quigley && .SHORT TERM... Issued 336 PM CDT Mon Aug 31 2026 Tonight through Tuesday night: A strong capping inversion with 200-250 J/kg of CIN has prevented scattered thunderstorms from nudging over the border into Wisconsin this afternoon. An isolated thunderstorm is still possible, but becoming less likely. Isolated to scattered showers are expected through this evening, ending around sunset. Highs in the mid 80s are expected, with heat index values in the low 90s. After sunset, temperatures will fall into the low 70s and winds calm as a frontal feature stalls over central Wisconsin. With dewpoints also in the upper 60s to low 70s, widespread fog is expected, with patchy dense fog possible in low-lying areas. Fog is expected to burn off shortly after sunrise on Tuesday as southwesterly winds increase again. With WAA through all levels and a morning break in the cloud cover, expecting high temperatures Tuesday to reach the upper 80s to 90 degrees. Heat index values are expected to be in the mid 90s in central Wisconsin where more cloud cover persists, and in the upper 90s farther south. Near the WI/IL border, heat index values may briefly reach 100 degrees. Tuesday afternoon into Tuesday evening, an additional period of isolated to scattered thunderstorms is possible (20-30% chances). Expecting lightning to be the primary threat, but cannot rule out an isolated storm becoming severe. with MUCAPE around 2500 J/kg and bulk shear of 35 to 40 kt. A cap remains in place, albeit weaker (approximately 100 J/kg of CIN), but a strong trigger is lacking for adequately organized storms. Main trigger will be broad WAA aloft, which would lend credence to more of a scattered thunderstorm threat than an organized severe threat. Late Tuesday night into Wednesday, an 850 LLJ noses into central Wisconsin where the weak frontal boundary lingers, bringing more confidence for scattered storms, but still low confidence for severe activity (20-40% chances). MH && .LONG TERM... Issued 336 PM CDT Mon Aug 31 2026 Wednesday through Monday: Wisconsin remains on the northern edge of 500 mb ridging through the end of the work week, with chances for convection/ridge riding MCSs through Friday and lingering high heat and humidity through Thursday. Individual 500 mb shortwaves and LLJs will be the driving force for storms through the week, with exact timing and placement likely not becoming clear until 24 hours from the each event. Currently, highest confidence in widespread storm development for southern Wisconsin is Wednesday night into Thursday, as broad low pressure develops in the central Plains and brings a stronger, more focused LLJ to eastern Iowa and southwestern Wisconsin. This would support a severe threat due to the enhanced CAPE, moisture, and more focused trigger and tend to like the NBM 50-70% PoPs going into Thursday morning. As low pressure deepens in the Northeast U.S. on Friday, high pressure builds into Ontario, bringing drier, northeasterly flow to the Great Lakes and bringing a return to drier conditions and more seasonable temperatures for the weekend into Monday (highs in the low 80s). MH && .AVIATION... Issued 625 PM CDT Mon Aug 31 2026 VFR flight categories prevail across southern Wisconsin early this evening. Widely scattered rain showers will linger through the first half of the evening, particularly in east-central Wisconsin and near the Wisconsin-Illinois state line. Have thus introduced TEMPO -RA groups through 02Z at SBM and JVL in the 00Z forecast. Whether/not state line activity persists long enough to reach the vicinity of ENW remains uncertain, with radar trends being monitored for possible TEMPO groups into the mid-evening hours. Still anticipating areas of fog development overnight, with short-term model guidance hinting at the greatest potential for VIS reductions across the west where cloud cover is forecast to be thinner. Have thus continued VIS reductions & BR mentions at MSN and JVL during the predawn hours in the 00Z forecast. Greater anticipated cloud coverage further east casts some uncertainty regarding fog potential closer to Lake Michigan, so have for the time-being removed any BR mentions at eastern fields given lower forecast confidence. Will be closely monitoring vis trends for any changes to VIS forecasts through the overnight. Quigley && .MARINE... Issued 336 PM CDT Mon Aug 31 2026 Low pressure of 29.5 inches over the Canadian Prairies will lift northeastward into the Hudson Bay through Tuesday, bringing continued breezy southwest winds to Lake Michigan through Tuesday. A Small Craft Advisory is in effect through this evening for gusty southwest winds from Port Washington southward. With a warm, moist airmass moving northward, patchy dense fog is also expected overnight into Tuesday morning. A front from the Canadian low will settle over the Lake tonight, lingering through the week and allowing for on- and-off thunderstorms through Friday. Meanwhile, high pressure around 30.0 inches of the Southeast U.S. will keep winds generally southerly through Wednesday. Thursday, low pressure finally exits into the Canadian Maritimes, bringing the front into the Ohio Valley and allowing winds to shift to northeasterly, remaining northeasterly through Friday. MH && .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