Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
Issued by NWS Milwaukee/Sullivan, WI
803 FXUS63 KMKX 160844 AFDMKX Area Forecast Discussion National Weather Service Milwaukee/Sullivan WI 344 AM CDT Wed Jul 16 2025 .KEY MESSAGES... - Very warm and humid conditions today with maximum heat indices in the lower 90s for the first half of the day. Increased shower and thunderstorm chances through the afternoon (50-80%) with lower chances (20%) lingering late this evening. - Continued potential (risk 2 out of 5) to see a broken line of strong to severe thunderstorms this afternoon/evening capable of producing damaging winds. - Heavy rainfall with 1-2 inches will be possible this afternoon/evening, especially for areas north of I-94 where localized pockets of >2 inches will be possible and result in minor flood concerns for low-lying and urban areas. - Looking cooler and drier Thursday into Friday with high temps in the 70s and lows in the 50s to around 60F. May see elevated swim risk conditions Thursday, especially for areas south of Port Washington to the WI/IL lakeshore border. - Unsettled weather returns for the weekend with 30-50% shower and storm chances Saturday and Sunday night. && .SHORT TERM... Issued 339 AM CDT Wed Jul 16 2025 Today and Tonight: Will warm up fairly quickly through the morning with 80s by mid- morning and muggy dewpoints creeping into the 70s. These conditions will set the stage for our thunderstorm and heavy rainfall potential this afternoon as a mid-level shortwave trough and supporting upper- level dynamics work their way across southern WI. The latest 00z suite of models continue to favor a broken line of thunderstorms along with moderate to heavy rainfall to develop over southwestern WI early this afternoon and progress east-norteastward as an MCV is progged to lift through the early evening. By sunset the bulk of upper- level forcing shifts east as a surface cold front pushes through southern WI. Looking at northerly winds with a cooler and drier airmass to settle in overnight into Thursday behind the cold front. Severe Thunderstorm Potential: While models have waffled over the past few days, we can now see the whites of the MCV eyes which will be one of the main focuses for this afternoon stronger to severe thunderstorm potential. Currently the MCV sits over the NE/SD/IA border with a decaying area of convection along it. Expecting the downward trend in the convection to continue as much of the CAM guidance along with short-range models prog this feature to lift across IA through the morning then pushing into southwestern WI early this afternoon. System is progressive and looks to push out over Lake Michigan later this evening. Accompanying the MCV will be a surface cold front behind it. So ample surface level forcing to pair with the mid-level shortwave trough along with a narrow band of 700mb frontogenesis, 850mb WAA, and nose of a 25-30kt LLJ to support the convective development this afternoon. While there is always a degree of uncertainty when it comes to MCV, there has been a consistent signal between the models for a north to south orientated line of thunderstorms to develop as the MCV moves across southern WI. Main timing window for this activity is between 17z-00z. With ample surface and upper-level forcing aligns in the warm sector of this system, the question shift to severe potential. Overall, instability builds ahead of the MCV with HREF min SBCAPE exceeding 1000 J/kg and mean SBCAPE values approaching 2000 J/kg. However the higher instability values favor southern half of the CWA. Meanwhile the deep layer shear (0-6km) is fairly meager (20-30kt) with the higher values (35 kt) favoring the northern half of the CWA. So while the severe potential exist across all of southern WI, there is a bit of an offset between these higher values of these two parameters. Where the higher values overlap will favor the better severe potential, which based on the 00-06z CAMs is along and on either side of the I-94 corridor. Main concern with any stronger to severe thunderstorms embedded within the line will be the damaging wind threat as DCAPE values are progged to exceed 1000 J/kg and steep low-level lapse rates (>7C/km). As stated above overall shear looks minimal and same can be said for the 0-1km shear with most models progging values less than 20 kt. While the overall tornado potential remains low, cannot complete rule out the potential for a brief spin up or two given the MCV forcing producing a locally enhanced pocket of 0-1km shear near it. Severe potential will quickly wind down after 00z as the MCV moves out over the lake and the cold front pushes through the area. Heavy Rainfall Potential: On the other side (northern portions) of MCV, there is a potential to see heavy rainfall mainly across our central WI counties (Marquette over to Sheboygan Co.). This is where the higher PWATs exceeding 1.75 and even 2 inches align with the warm frontal feature and the MCV. This is where a more west to east orientated band of convection could develop and move over the same area producing 1-2 inch rainfall with localized pockets potential exceeding 3 inches. However, at this time overall confidence to see widespread flash flooding and and flooding remains on the lower side as the latest 00- 06z model trend this west to east line to track a bit further north into the Fox River Valley. Also the progressive nature of this activity along with this area not seeing any significant rainfall recently favors any Flash Flood concerns to be localized. Nevertheless will be something to monitor through the morning to see if trends shift things a bit further south and slows down. Wagner && .LONG TERM... Issued 339 AM CDT Wed Jul 16 2025 Thursday through Tuesday: A few showers are possible Thursday morning, although the forecast is trending drier. The cold front will finally make it into southern WI by midday and clear the WI/IL border by late afternoon. High pressure, lower dewpoints and cooler temperatures will be a welcome relief for Thursday night and Friday. A little bit of the heat and humidity will begin to return Saturday, along with shower and thunderstorm chances. A weak shortwave is expected to track along a stalled frontal boundary that should be draped across northern IL Saturday morning. That shortwave will be convectively-induced, so there is a lot of uncertainty in its timing and track. Meanwhile, a synoptic shortwave should be crossing northern WI. Between the two ripples in the upper flow, there will be thunderstorm chances for southern WI Saturday afternoon and evening, but there is uncertainty about strength and coverage. A similar setup Sunday may bring additional storms, but there is more uncertainty in this occurring. One more upper trough is expected to track across the Upper Midwest Monday-Tuesday. After that, models diverge significantly, with some bringing an upper ridge with heat and humidity to southern WI, and others bringing unsettled weather with repeated shortwaves. Cronce && .AVIATION... Issued 339 AM CDT Wed Jul 16 2025 VFR conditions and light southerly winds early this morning. Will see winds increase through the morning along with cloud cover ahead of an approaching low and cold front. Expecting a line of thunderstorms to develop early this afternoon (17-18z) across southwestern WI and push eastward through the evening. With any thunderstorms impacting southern WI terminals can expect heavy rains and gusty winds dropping visibilities and ceiling down to lower MVFR/IFR levels. Will see the heavier shower and thunderstorm activity push out of the region later this evening (00z-03z), but some showers may linger through 006z across central WI. Then northerly winds expected behind the cold front overnight into Thursday along with improving flight conditions. Wagner && .MARINE... Issued 339 AM CDT Wed Jul 16 2025 Southerly winds will increase this morning ahead of an approaching low pressure and accompanying front. Expect the low pressure over IA to move across southern WI this afternoon and cross the middle portion of Lake Michigan through the evening. Accompanying this system will be increased thunderstorm chances which may produce strong, gusty winds across Lake Michigan through the late afternoon and evening. Will first see northerly winds gradually build down across the northern half of the lake through the afternoon as the front shifts southeast ahead the low pressure, which will move across the Lake later this evening/tonight. Expect breezy northerly winds to migrate into the southern half of the lake overnight and persist into Thursday as high pressure builds into the Upper Midwest. Lighter, shifting winds are expected for Friday as the high pressure moves over the Upper Great Lakes. Increasing southerly flow then returns for the start of the weekend. Wagner && .MKX WATCHES/WARNINGS/ADVISORIES... WI...None. LM...None. && $$ Visit us at weather.gov/milwaukee Follow us on Facebook, Twitter, and YouTube at: www.facebook.com/NWSMilwaukee www.twitter.com/NWSMilwaukee www.youtube.com/NWSMilwaukee