Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
Issued by NWS Milwaukee/Sullivan, WI
335 FXUS63 KMKX 211100 AFDMKX Area Forecast Discussion National Weather Service Milwaukee/Sullivan WI 600 AM CDT Fri Aug 21 2026 .KEY MESSAGES... - Showers and thunderstorms (non-severe) are likely for east central WI this morning, with a chance elsewhere. - Scattered showers and thunderstorms (30 to 50 percent chances) with passing cold front are expected this afternoon and evening. Damaging winds are the main threat. - Small chances (20 to 40 percent) for a shower or storm Saturday afternoon for portions of east central and southeast Wisconsin. && .UPDATE... Issued 600 AM CDT Fri Aug 21 2026 The ongoing showers and thunderstorms over central WI are focused along the nose of the low level jet and 700mb moisture axis. There is also weak 500mb vorticity advection and a coupled upper jet feature. The expectation is that the storms could expand southward into portions of south central WI (but north of Madison) this morning, but also gradually diminish as they approach Lake Michigan due to the LLJ weakening. The axis of MUCAPE greater than 500 j/kg is on the tail end of these storms, from Juneau/Adams counties to La Crosse, so the storms are not overly strong. Winds will be steady out of the southwest today, and we can expect an increase in the dewpoints due to moisture advection this afternoon. This will help increase our instability, especially if we get plenty of sunshine behind the morning convection. Isolated to scattered storms should develop over south central WI by mid afternoon. The trigger point for these is a little uncertain, as we will have an upper trough overhead with weak vorticity advection and then a surface trough approaching. Nevertheless, with up to 2000 j/kg of CAPE and bulk shear of 20 to maybe 30 kt, a few strong to severe storms are possible this afternoon and evening. Damaging winds are the main threat, but with lower- end severe potential of gusts up to 60 mph. Hail is possible but without the balanced instability/shear environment it will be difficult to sustain an updraft. The tornado potential is non- zero, but also seems pretty small. The 0-3km shear vectors are only around 20 kt, but any localized boundaries (outflow, surface front, lake breeze, etc.) could help increase that speed. The conditions are seeming favorable enough for SPC to upgrade most of southern WI and northern IL into a Slight Risk for severe storms. Cronce && .SHORT TERM... Issued 1100 PM CDT Thu Aug 20 2026 Tonight through Saturday night: Tonight should remain largely quiet outside of a few light showers nudging into the region but despite some PVA pushing through and low level WAA the low level moisture may be too dry initially to bring showers to the ground. Around daybreak Friday we expect some low level moisture to allow for precip chances to increase for a brief period in the morning. The forcing appears to be largely focused along the shortwave with supplementary WAA and better moisture but CAMs do not seem to favor widespread showers in the morning with better chances focused further west closer to the surface front. As the front pushes east moisture seems to improve into Friday afternoon and evening. CAMs seem to favor some development of convection Friday late afternoon on the western half of the CWA with a secondary development potential into the early evening closer to the lake. Given higher instability (>2000 J/kg) and enough shear (30-35kts) we should see a stronger storm or two for a brief period but the lack of better shear should limit the potential to just a few storms at most with the primary concerns being 1 inch hail and brief damaging winds. Quieter conditions overnight Friday into Saturday morning as the surface low pushes out. However, Saturday late morning and afternoon we will likely see a backdoor cold front combined with lake breeze convergence zone in the nearshore region bring additional precip chances for eastern portions of the CWA. There is some uncertainty for this primarily with respect to low to mid level moisture and how widespread it will be but some showers and perhaps a few storms will be possible with this. If we can manage a few storms we could see some become strong given a decent amount of deep layer shear though this differs significantly between the CAMs and synoptic scale models so we will have to monitor those conditions through Friday. This will be worth monitoring Saturday afternoon given some potentially sneaky conditions. Chances will rapidly decrease Saturday evening as we lose instability and forcing pushes out. Kuroski && .LONG TERM... Issued 1100 PM CDT Thu Aug 20 2026 Sunday through Friday: Sunday and Monday will feature high pressure building into the region keeping things dry through Monday. Things have trended overall drier into Tuesday with the high pressure lingering a bit longer with Tuesday night Wednesday becoming our next best chance for showers and storms as and 850mb front and upper level shortwave swing through with some WAA. Still some uncertainty in track and timing but models generally agree on this pushing through bringing precip with likely some storms as well. In addition, deep layer shear appears to be strong in the 40-50kt range which would bring some severe risk if the timing of storms is into the evening. After Wednesday, uncertainty increases quite a bit though in general higher pressure seems to be pushing in with drier conditions overall more likely. Kuroski && .AVIATION... Issued 600 AM CDT Fri Aug 21 2026 Storms (non-severe) are likely for east central WI, but are looking less likely for south central and southeast WI this morning. Cloud bases in any storms toward central WI could drop to 2500ft, but would be around 5000ft elsewhere. Look for steady southwest winds across southern WI today with a general lull in storm activity. Then isolated to scattered storms are expected to develop in south central WI mid afternoon and trek eastward through early evening. A few strong to severe storms are possible with damaging winds the main threat. Winds will become northwest this evening after the passage of a cold front. Cronce && .MARINE... Issued 600 AM CDT Thu Aug 20 2026 South to southwest winds will increase today as a low pressure trough of 29.8 inches approaches southern Wisconsin from the Minnesota Arrowhead. Thunderstorms are expected at times today through tonight. The 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. 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