528 FXUS63 KGRB 291720 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 1220 PM CDT Mon Jun 29 2026 Updated aviation portion for 18Z TAF issuance .KEY MESSAGES... - An Extreme Heat Warning is in effect from this afternoon through Tuesday for central Wisconsin and the Fox Valley. A Heat Advisory is in effect for the rest of northern and northeastern Wisconsin for the same time period. - High heat and humidity will result in continued heat-related impacts for the middle to late part of the week. - Gusty onshore southerly winds will result in high waves and dangerous currents on Lake Michigan beaches through Tuesday evening. - Periodic chances for thunderstorms expected at times this week. Some of these storms could become strong or severe. Main hazards would be damaging winds, large hail, and heavy rain. && .DISCUSSION... Issued at 1257 AM CDT Mon Jun 29 2026 Severe Weather Potential This Morning... Convection is having issues getting going across the region as a warm front lifts north across the region. A recent KGRB RAOB sounding indicates this activity is fighting several capping inversions and dry air aloft, which will probably not be overcome overnight. Therefore, isolated to scattered thunderstorms are anticipated this morning instead of a huge MCS rolling through the region. This dry air and elevated warm layers should act to limit the severe weather potential this morning. Storms tonight and Tuesday Night... Ample moisture and heat will provide the instability for storm development through the upcoming week. However, lingering warm air aloft will limit surface based storms at times. Thus, the placement of the upper ridge and associated '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 tonight into Tuesday, but will largely initiate 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 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 today and Tuesday. With the strong heat signal over central Wisconsin and probabilistic guidance still suggesting around 60-80% chance of exceeding 104 heat indices, will keep the current headlines of 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. There is also a signal on Tuesday that southern Oconto and southern Marinette counties may reach Extreme Heat Warning criteria Tuesday afternoon; however, will hold off on any upgrades for these areas since overnight convection or clouds could impact temperatures on Tuesday. 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. Depending on how these convective trends and clouds play out, an extension of heat headlines is not out of the question. 4th of July Weekend... Taking a peek into the 4th of July weekend, current trends keep the dangerous heat across the region on Friday, then push the warmest air to the south Saturday and Sunday as a semi- stationary front remains across Wisconsin. This will come with a downside, as there will be lingering chances for showers and thunderstorms at times as the front becomes the focus for convection as several shortwaves track along the zonal flow across the western Great Lakes region. At this time the best window for convection appears to be Friday afternoon and Friday night as well as Saturday afternoon into Saturday night; however, given how far out this forecast is this could easily move to a different periods based on what happens earlier in the week. Although the risk for severe weather is difficult to assess this far out, the warm, moist airmass will provide instability, which means strong to severe storms are certainly a possibility for the weekend. Currently temperatures look to stay in the upper 80s to lower 90s on Friday, then cool slightly into the 80s Saturday and Sunday. Heat index values on Friday will still be well into the 90s, with values possibly approaching 100, cooling into the lower 90s by Saturday and Sunday. Despite the "cooler" temperatures, we will be coming off a prolonged period of hot weather; therefore an extension of warm temperatures through the weekend may have a compounding effect. && .AVIATION...for 18Z TAF Issuance Issued at 1220 PM CDT Mon Jun 29 2026 Low clouds continue to lingering the region this afternoon, providing IFR to MVFR ceilings for much of the area. As temperatures continue to rise through the afternoon, ceilings should continue to lift, especially for central to east-central Wisconsin, which should see the greatest improvement in flying conditions. Tonight, some low cloud cover or fog may return as temperatures drop again across the region. This may limit visibility at times in many areas. Winds will be out of the south this afternoon and tonight with gusts up to 15 to 20 knots during the afternoon. && .GRB WATCHES/WARNINGS/ADVISORIES... Heat Advisory until 7 PM CDT Tuesday for WIZ005-010>013-018>021- 073-074. Beach Hazards Statement until 10 PM CDT this evening for WIZ022- 040-050. Extreme Heat Warning until 7 PM CDT Tuesday for WIZ022-030-031- 035>040-045-048>050. && $$ DISCUSSION.....Kurimski AVIATION.......Uhlmann