479 FXUS63 KMKX 300115 AFDMKX Area Forecast Discussion National Weather Service Milwaukee/Sullivan WI 815 PM CDT Mon Jun 29 2026 .KEY MESSAGES... - Extreme Heat Warning in effect for all of southern WI tonight through Wednesday. Additional heat headlines may be needed for the second half of the week, but some uncertainty remains due to clouds and rain chances. - Thunderstorm chances return Tuesday night through the end of the week as the hot and humid pattern continues. - High swim risk conditions for Ozaukee and Sheboygan County beaches this evening, with moderate swim risk conditions for Milwaukee and Racine Counties. && .UPDATE... Issued 815 PM CDT Mon Jun 29 2026 Convective initiation is occurring near the cold front over the ern Dakotas into ne NE early this evening. The associated low pressure area of 995 mb over ern ND will deepen to 985 mb over sw Manitoba by 12Z Tue as the main upper wave swings nwd from the Dakotas. Thus the cold front will weaken as it lifts newd from wrn MN into ne MN. The 850-300 mb flow remains swly tnt over said region, while the forward propagating corfidi vectors have a sswly flow. Thus expect any MCSs to track newd through MN toward nw WI. Otherwise sswly sfc winds will maintain a hot and humid airmass over srn WI into Tue and Wed. The Extreme Heat Warning is in effect through Wed at this time. Showers and storm chances of 20-40 percent are forecast Tue nt along and west of a line from Darlington to Madison to Sheboygan then shifting even farther toward central WI on Wed as the main shortwave track runs from the central Great Plains to MN and nrn WI. Gehring && .SHORT TERM... Issued 247 PM CDT Mon Jun 29 2026 Tonight through Wednesday: Hot and humid is the name of the game through the first half of the week as the upper-level ridge is set up over the Midwest with a blocking high over the southeastern CONUS. Extreme Heat Warning has been extended through at least Wednesday at this point given the prolonged nature of daytime heat indices expected to rise above 100F each afternoon and overnight heat indices in the upper 70s. Areas immediately along the lakeshore of Lake Michigan along with any onshore wind component may be cooler by a few degrees, but still will see impacts from the heat/humidity regardless. Even with cloud cover lingering this afternoon, we are seeing heat indices above 100F and even higher with pockets of clearing and dewpoints running warmer than models suggested. Thus, have higher confidence of seeing similar heat indices Tuesday into Wednesday. While the hot and humid conditions are the main story, these conditions are also favorable ingredients for thunderstorm activity. It will not take much to trigger a storm or two to develop with these conditions, however, it needs a trigger to initiate development and tap into the moisture and instability settled across the region. Each CAM has a different solution and potential trigger for any activity overnight and Tuesday, but its tough to pinpoint if and what type of trigger would be. The 12z NAM nest, and ARW have convection upstream be the focus for some showers and storms to develop overnight and track across and north of the area, with the RRFS being more aggressive with deeper develop more into Tuesday off of something coming off the storms that may develop in the Plains tonight (which seems most unlikely scenario, but not impossible). Meanwhile the HRRR and NSSL keep us dry and any convection to the north. So while potential is there and cannot rule out seeing a few storms trigger along remnant boundaries or a gravity wave from upstream storms, the influence and subsidence from the ridge may ultimately limit any of this activity Tuesday, but Wednesday might have better potential as the ridge axis shift further east and upper- level jet influence creeps toward our western CWA. Nevertheless, it does bear watching the mesoscale trends and how the environment evolves overnight through Tuesday. Wagner && .LONG TERM... Issued 247 PM CDT Mon Jun 29 2026 Wednesday night through Monday: Hot and humid conditions persist into the second half of the week with additional heat headlines possible given persisting +100F heat indices. However, pattern remains more uncertain as the ridge axis slide further east and potential for daily shower and thunderstorm chances increase. Models hint at a bit more upper-level support in the form of mid-level vorticity lobes overrunning the ridge along with LLJ and upper-level jet moving more in place. Thus, could see the extreme heat pattern break down a bit into the holiday weekend. Nevertheless, still looking at above normal temps and muggy conditions accompanying the daily storm chances for the end of the week. Wagner && .AVIATION... Issued 815 PM CDT Mon Jun 29 2026 Sct035-045 cumulus or stratocumulus will continue tnt-Wed with areas of broken cloud cover possible at times. Gehring && .MARINE... Issued 247 PM CDT Mon Jun 29 2026 Southerly winds will continue this afternoon into the evening but gradually shift southwesterly. Given the humid airmass and cooler airmass will be potential for fog over Lake at times, particularly the northwestern quadrant of the Lake along northeastern WI to mid lake. Otherwise, with low pressure developing over the Plains and high pressure lingering over the Southeast US, expect breezy conditions to continue through much of the week. The hot and humid airmass settled over the region will also bring daily thunderstorms chances to portions of the lake through the end of the week. Wagner && .MKX WATCHES/WARNINGS/ADVISORIES... WI...Beach Hazards Statement...WIZ052-WIZ060 until 10 PM Monday. LM...Dense Fog Advisory...LMZ563 until 7 AM Tuesday. Small Craft Advisory...LMZ643-LMZ644-LMZ645-LMZ646 until 10 PM Monday. && $$ 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