147 FXUS63 KGRB 291815 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 115 PM CDT Mon Jun 29 2026 Forecast discussion for routine afternoon forecast 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 115 PM CDT Mon Jun 29 2026 Storms Potential the Next Couple of Days... 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. Tuesday the ample heat and moisture in the region during the afternoon will provide for significant instability at the surface under relatively weaker capping than today. Timing of convective initiation remains tricky, but generally suggest development along a weak surface boundary before following the instability into our area. Shear around 40-50 knots will serve to organize storms and will likely lead to more progressive systems that move relatively quickly across the area. Therefore would expect damaging winds and heavy rainfall to the be primary severe weather concerns for the region. Additional convection is then possible again overnight as another guidance brings another weak shortwave and accompanying warm air advection into the region late overnight into Wednesday. If we get two rounds in the same areas, may need to watch for any lingering boundaries and intensification. Wednesday... Active weather potential continues into Wednesday as get closer to the edge of the 'heat dome' to our east. A surface boundary stretching over the Upper Midwest through northern Wisconsin on Wednesday, which may serve to sustain any ongoing overnight convection mentioned above or to help redevelop additional storms during the afternoon and evening period later in the day. Storm timing/location will heavily depend upon the details of convection the previous 48 hours; but strength potential-wise there will be ample heat and instability to work with to produce some stronger storms during the afternoon and evening. Dangerous Heat... Dangerous heat works its way into the region this afternoon. Dewpoints have already pushed well into the 70s across the region, making the outdoors feel very muggy if not tropical. As cloud cover scatters out expected temperatures to make a push towards the 90s across central to east-central Wisconsin, pushing heat indices into the upper 90s to lower to mid 100s. Only northern Wisconsin may see temperatures a few degrees cooler, as the robust low clouds cling on for a few more hours and lower daytime highs a couple of degrees. Still, probabilistic guidance remains in good agreement on heat indices over 104 today and again on Tuesday, so will continue the Extreme heat Warning. 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 remains a a signal on Tuesday that southern Oconto and southern Marinette counties may reach Extreme Heat Warning criteria Tuesday afternoon; however, will continue 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 heat related impacts than those further inland. North of the Extreme Heat Warning, heat indices are expected to hit the 95-99 range, which would be just below typical heat criteria. 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, the Heat Advisory remains in the forecast. 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 while heat indices remain in the 90s. 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... Looking ahead to the 4th of July weekend, current trends suggest the heat will linger in the region on Friday before pushing southwards over the weekend. 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, relying heavily on peak heating for instability. With how far out this forecast still is, changes in the timing are certainly possible. Storm strength also remains difficult to assess this early, but given the ample expect moisture and instability, strong to severe storms are certainly a possibility for the weekend. Temperature-wise we are expected to cool slightly into the 80s Saturday and Sunday but 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. As mentioned for heat above, compounding extended heat may still a compounding effect for the region despite the 'cooler' temps, especially as people are more prone to spend their extended time outdoors for the holiday. && .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.....Uhlmann AVIATION.......Uhlmann