NWS Milwaukee Forecast Discussion
520 FXUS63 KMKX 040013 AFDMKX Area Forecast Discussion National Weather Service Milwaukee/Sullivan WI 713 PM CDT Thu Sep 3 2026 .KEY MESSAGES... - Periods of showers and storms will be possible through Friday, with tonight`s round capable of producing strong to severe thunderstorms. Damaging winds and heavy rainfall are expected to be the main hazards. - Drier weather expected for the weekend into early next week, with warm and humid conditions persisting. && .UPDATE... Issued 704 PM CDT Thu Sep 3 2026 Rain should hold off this evening, but we are currently monitoring west central MN as the location where thunderstorms may develop and then track into Wisconsin during the overnight hours. Local obs and mesoanalysis data indicate that a primary and secondary warm front are draped over the UP of Michigan and through central Wisconsin, respectively, and both connect to an area of low pressure near Fargo, SD. Theta-e advection has been noted to be strongest in this area late this afternoon into the early evening. As a low level jet kicks in during the overnight hours, the theta-e advection over the boundaries should increase in strength, leading to more widespread convective initiation. This convection is then expected to track ESE along the sfc warm front/CAPE gradient. If this scenario plays out, the NE half of our CWA would be in line to see a complex of storms roll through the area between 5am to 8am Friday morning, while the SW half of the CWA sees more hit or miss storms. Damaging winds would be the main severe weather hazards, though heavy rain and localized flooding would also be possible given the high PWATs from 1.8 to 2 inches over the region, and the high likelihood that storms will track repeatedly over the same areas overnight into Friday morning. One potential failure mode or something that could change the course of the overnight convection is the current convection that is ongoing over north central WI. This could either push the instability gradient southward or overturn favorable instability out ahead of the expected storms. This lends a bit of uncertainty to the exact track of the storms overnight. These storms may also arrive in east central Wisconsin sometime this evening if they hold together. CMiller && .SHORT TERM... Issued 326 PM CDT Thu Sep 3 2026 Tonight through Friday night: We have a surface frontal boundary draped across southern WI this afternoon. It has not moved much since early this morning. We have southerly winds and high dewpoints (greater than 72F) south of a line from the Dells to Watertown to Menomonee Falls, and a slightly different air mass north of there (dewpoints 67-72 and lighter east-northeast winds). This boundary will continue to carry a chance for showers and a few thunderstorms through late evening, despite the meso model forecast reflectivity field showing that area clear. Meanwhile, the low level jet will ramp up again this evening and likely nose all the way into northern WI and the northern portions of east central WI (between Sheboygan and Green Bay). This will be our area to watch for scattered thunderstorms to develop between 8 and 10 PM, and a few could be strong. This would be in an environment favorable for gusty winds (downbursts) and hail with modest CAPE and shear. This cluster of storms is expected to slide southeast and could clip east central WI including Fond du Lac and Sheboygan. The storms that just developed and tracked through Grand Forks, ND this afternoon are what we are watching for our overnight thunderstorm/severe chances. The broken line of storms should arrive in central WI around 1 AM (they may catch up or merge with the LLJ storms in east central WI). The 18Z HRRR is now tracking this line farther north across northern WI and not through east central/southeast WI. This might be picking up on a LLJ and CAPE gradient that is farther north than what the 12Z models and especially the 06Z models were picking up on. If this line of storms tracks into southern WI late tonight, it will exit southeast WI around 8 or 9 AM Friday. Damaging winds would be the main threat, but we cannot rule out hail or an isolated tornado. However, the storm motion will slow down toward morning. With precipitable water values of nearly two inches and the potential for training storms, heavy rain and flash flooding will become a larger concern. If the line misses us, then a stalled outflow boundary will be one to watch for additional convective development Friday afternoon (which the HRRR is showing). Timing of afternoon/evening convection Friday is highly dependent upon how quickly the morning storms and clouds clear. If there is ample time with sunny skies, then there is a higher risk for a few strong/severe storms. Again, damaging winds would be the main threat with hail and tornado a more isolated threat. Cronce && .LONG TERM... Issued 326 PM CDT Thu Sep 3 2026 Saturday through Thursday: The stalled frontal boundary is expected to get pushed to the southwest of Wisconsin on Saturday as the upper ridge lifts into MN and a more amplified trough develops over the eastern Great Lakes. The frontal boundary may trigger a few showers and storms (similar location as a lake breeze) midday through evening Saturday so we are carrying chance pops. With northeast to easterly winds across all of southern WI on Sunday and the frontal boundary shunted to our west, we have a dry forecast on Sunday and Monday. Highs will be much lower than previous days, ranging from the upper 70s east to the lower 80s west on this holiday weekend. Our precip chances will return to southern WI Tuesday as the warm and humid air returns due to low pressure tracking from the Northern Plains into Ontario. This will be another situation where a frontal boundary could stall over southern WI and be the focus for continuous chances for showers/storms through the rest of the work week. Cronce && .AVIATION... Issued 713 PM CDT Thu Sep 3 2026 VFR should persist through the evening, though some lakeshore terminals may see some marine fog advect inland around 06z in afterward, introducing some vis restrictions. Thunderstorms are expected to start as early as 06z in east central WI with their number/coverage becoming more widespread toward daybreak on Friday. Ceilings with convection are expected to be between 1500 to 3000 feet. Areas over southwest Wisconsin may miss out on the lions share of the thunderstorms activity and stay in VFR. CMiller && .MARINE... Issued 326 PM CDT Thu Sep 3 2026 A frontal boundary will remain across the Great Lakes region through Friday. As this frontal boundary waffles north to south across the lake from day to day, generally east to northeast winds are expected north of the front, with east to southeast winds south of the front. On and off thunderstorms will be possible along and north of this frontal boundary through at least Friday night. Then high pressure around 30.1 inches builds over Hudson Bay on Saturday, while low pressure around 29.6 inches moves into the northern Great Plains. Similar to earlier week storms, widespread severe weather is not anticipated, though isolated stronger storms with hail and gusty winds are possible. Cronce && .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