166 FXUS63 KGRB 282334 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 634 PM CDT Sun Jun 28 2026 Updated aviation portion for 00Z TAF issuance .KEY MESSAGES... - Small chance of thunderstorms (20-30%) over central and north- central Wisconsin this afternoon. - Strong to severe storms possible tonight and again on Monday night. Main hazards would be damaging winds, large hail, and heavy rain. - Periodic chances for thunderstorms Tuesday through the end of the week. Some of these storms could become strong or severe. - High heat and humidity will result in heat-related impacts for much of the upcoming week. Most oppressive conditions expected Monday and Tuesday. - An Extreme Heat Warning is in effect Monday afternoon and evening for central Wisconsin and the Fox Valley. An Heat Advisory is in effect for the rest of northern and northeastern Wisconsin. && .DISCUSSION... Issued at 228 PM CDT Sun Jun 28 2026 Severe Weather Potential Today and Tonight... A decaying MCS will bring a brief chance of rain to the area along with widespread high cloud cover, but is expected to have minimal impact during the afternoon. Assosciated precipitation will have around a 20-30% chance of reaching the surface. The main focus of the active weather today will be for storms tonight (60-90% chance) as a surface warm front lifts into the region. Keeping with previous forecasts, the LLJ now ramps up a couple hours sooner, with short-term guidance suggesting initation as early as a couple hours before midnight across western and central Wisconsin before expanding storms eastwards into the rest of the area. The warm front will bring a surge of instability and ample moisture, providing the means for organized convection and strong to severe storms overnight. Damaging winds and very heavy rainfall will be possible with any storms. Abundant PWATs pushing upwards of 2 inches do suggest that some areas may see very localized rainfall amounts over an inch under the stronger storms. This will likely not be widespread by may need watching if storms train over an area. The area is in the Marginal Risk (5% chance) of excessive rainfall. As for hail, models have increased the available instability aloft through the hail growth zone over the last 24 hours, which would support getting hail to the surface despite the deeper warm layer. Finally, the earlier start time has also moved up the departure time of precipitation Monday morning, with drier conditions spreading across the area by the mid-morning hours as capping establishes itself aloft behind the warm front. Storms Monday Night and Tuesday Night... Ample moisture and heat will provide the instability for storm development through the upcominn work week. However, lingering warm air aloft will limit surface based storms at times. Thus, the placement of the upper ridge and assosciated 'heat dome' over eastern CONUS will remain the critical components to watch for convective potential for our area. The first shortwave will cross the Upper Midwest Monday night into Tuesday, but will largely inititate in Minnesota. This system will then spread eastwards through the evening, but capping over our area should help weaken storms as they arrive. This will limit the best severe potential to our west, with the Marginal Risk currently limited to portions of central to north- central Wisconsin. This scenario then repeats Tuesday evening as the next shortwave arrives, but this time the ridge will be slightly more east, possibly bringing the storms more into our area. That said, the details of convection each day are muddy, largely depending on when/where storms developed the previous day. That said, the upper ridge is expected to continuing shifting eastwards through the work week, bringing us into the line of fire of any shortwaves along the upper ridge. Any storms Monday and Tuesday will have the potential to be strong to severe given the instability and moisture around. The most likely hazard will be very heavy rainfall, especially if storms repeat each day and soils become heavily saturated. Dangerous Heat... Active weather aside, the heat accompanying the upper ridge will be a hazard itself. Dewpoints well into the 70s accompanied by high temperatures into the 90s will bring heat indices well into the upper 90s to mid-100s Monday and Tuesday. With the strong heat signal over central Wisconsin and probabilistic guidance still suggesting around 60-80% chance of exceeding 104 heat indices, decided to convert the Extreme Heat Watch into an Extreme Heat Warning for all of central to east-central Wisconsin. The most likely areas to get the extreme heat will be central Wisconsin into the Fox Valley, but also included the lakeshore areas for the inland portions of the counties. Those living along the shoreline of Lake Michigan and north of Sturgeon Bay should see significantly lower impacts than those further inland. North of the Extreme Heat Warning, heat indices will remain just below advisory criteria during the afternoon, lingering in the 95-99 range. However, overnight temperatures are unlikely to drop below 75 in many areas, which typically means little relief from the heat for those without shelter and means of cooling. Given that this makes for a long stretch of heat, and also that the forecast keeps overnight temperatures up even as high temperatures drop slightly by Wednesday, decided to issue a Heat Advisory for the rest of the region. As we get into the mid to late week, heat indices should see a minor drop, but temperatures are currently forecast to remain in the upper 80s to lower 90s each day. The main complicating factor for headlines during this period will be convective weather, as any storms could provide some relief and lower the daytime high in some areas. On the other hand, the forecast keeps heat indices for most of the area above 70 through Friday, which would compound heat fatigue effects for those without shelter as mentioned above. && .AVIATION...for 00Z TAF Issuance Issued at 628 PM CDT Sun Jun 28 2026 Cloudy to mostly cloudy skies were noted early this evening along with low, mid, and high clouds. CIGs ranged from MVFR across central Wisconsin, to VFR across much of the rest of the region. An area of showers and thunderstorms across far east-central Wisconsin should slide southeast around the start of the TAF period. A thunderstorm complex is expected to develop to the west this evening north of an advancing warm front, then track through the TAF sites during the overnight hours and into Monday morning. This complex is expected to lower conditions to MVFR and eventually IFR as the storms move through the region. Highest confidence is across central Wisconsin, with a prevailing group for thunderstorms, with lesser but still high enough for a TEMPO group across north- central and east-central Wisconsin TAF sites. Some of these storms could be strong to severe, with damaging winds and large hail. Conditions should eventually improve back to VFR throughout the day on Monday as a warm front lifts north and skies clear from south to north. Winds will generally be southeast 10 to 20 knots, shifting to the south on Monday behind the warm front. && .GRB WATCHES/WARNINGS/ADVISORIES... Heat Advisory from noon Monday to 7 PM CDT Tuesday for WIZ005- 010>013-018>021-073-074. Beach Hazards Statement from 4 AM CDT Monday through Monday evening for WIZ022-040-050. Extreme Heat Warning from noon Monday to 7 PM CDT Tuesday for WIZ022-030-031-035>040-045-048>050. && $$ DISCUSSION.....Uhlmann AVIATION.......Kurimski