Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
Issued by NWS Milwaukee/Sullivan, WI
696 FXUS63 KMKX 122003 AFDMKX Area Forecast Discussion National Weather Service Milwaukee/Sullivan WI 303 PM CDT Sat Sep 12 2026 .KEY MESSAGES... - Active start to next week, with multiple periods of showers and thunderstorms expected Monday evening through at least Tuesday. Some storms could produce heavy rainfall and some gusty winds. - Gales are possible Monday night into Tuesday morning across the Lake Michigan open waters as increasing south winds develop. A Small Craft Advisory is likely Monday afternoon into Tuesday morning for the nearshore waters. && .SHORT TERM... Issued 303 PM CDT Sat Sep 12 2026 This afternoon through Tuesday: A dry cold frontal passage is expected this afternoon. Despite MLCAPE of 1500 J/KG, weak surface convergence and capping should prevent convective initiation in se WI. The broken stratocumulus cloud cover ahead of and along the front is an indication of the capping. Gradual cold advection on nwly sfc winds will then prevail tnt-Sun. Aloft, a fairly strong and fast shortwave trough will track from srn Canada across the nrn Great Lakes on Sun. The upper wave will help induce a west to east band of mid level frontogenesis across srn WI that could result in a few high based, light showers. Rain chances of 20-30 percent are forecast. A 1025 mb high pressure area will then move across srn WI Sun nt. Low temps in the lower to middle 40s are expected inland from the lake. High temps around 70F are forecast Sun- Mon. For Mon afternoon into Tue, cyclogenesis is expected from the nrn high plains to srn Hudson Bay. A sly low level jet of 50 kt will develop over the Upper MS River Valley Mon afternoon then veer across WI Mon nt-Tue AM. There are timing differences with the onset of low to mid level warm, moist moist advection and frontogenesis. The GEFS and ECMWF are slower and mostly hold off until Mon eve-nt, while the NAM and most CAMs begin widespread showers and scattered storms Mon afternoon especially well north and west of the MKE metro area. Will be following the NBM PoPs which is similar to the slower GEFS and ECMWF. PWATs of 2 inches will then overspread srn WI Mon nt as the thermal ridge shifts ewd and the low level jet veers into central and srn WI. There is some weakening of the approaching cold front for early Tue AM, but overall believe widespread showers and storms will likely occur over srn WI. MUCAPE is expected to remain below 1000 J/KG and elevated with heavy rain the main concern. Flash flooding would be possible if persistent training of storms occur, but there is uncertainty on longevity and placement of the more intense rainfall rates at this time. The antecedent conditions are also fairly dry with low river levels. Lesser rainfall amounts would then be expected on Tue as the low level jet and front weakens and slows as it passes through srn WI. Gehring && .LONG TERM... Issued 303 PM CDT Sat Sep 12 2026 Tuesday night through Saturday: Wswly flow aloft will continue for the week with a stationary front wavering north to south at times, and likely residing over IL much of the time. Rounds of warm, moist advection north of the boundary over srn WI will be possible at times during the week with additional showers and storms. By the end of the week, cyclogenesis may accompany a shortwave trough moving ewd across the Great Plains and bring more showers and storms to the region. Slightly below normal temps are forecast from Wed-Sat partly due to the potential for clouds and rain. Gehring && .AVIATION... Issued 303 PM CDT Sat Sep 12 2026 Areas of MVFR Cigs this afternoon with widespread VFR conditions expected tnt-Sun. Gehring && .MARINE... Issued 303 PM CDT Sat Sep 12 2026 A cold front will move across Lake Michigan late this afternoon with modest southwest winds shifting west northwest. Modest northwest winds will then prevail tonight and Sunday until high pressure around 30.3 inches moves across the lake late Sunday night into Monday morning. Winds will increase and veer south southwest Monday night into Tuesday as low pressure around 29.4 inches develops over Manitoba. Gales appear likely during this time frame. Periods of showers and thunderstorms will accompany the developing low from as early as Monday evening into Tuesday. Winds will trend northerly and weaken behind a cold front Tuesday night into Wednesday. A Small Craft Advisory will likely be needed Monday afternoon into Tuesday morning for breezy south winds and high waves. Gehring && .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