Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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884 FXUS63 KGRB 210418 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 1118 PM CDT Mon May 20 2024 Updated aviation portion for 06Z TAF issuance .KEY MESSAGES... - Impactful strong to severe storms are anticipated across portions of the area Tuesday. The areas most likely to see severe weather will be central to east-central WI and southwards. Damaging winds, large hail, and a few tornadoes will be possible with stronger storms. - Heavy rainfall on Tuesday may also pose a flooding concern. && .DISCUSSION... Issued at 331 PM CDT Mon May 20 2024 Short Term...Tonight and Tuesday The upper trough that brought rain and some thunderstorms to areas of central and east-central Wisconsin will gradually move eastwards and out of the region by the evening hours today. A few showers and some brief thunder may still cross portions of the central to southern Fox Valley through Manitowoc, but most of the area will see quieter conditions move back in to the region for the rest of the day. Tonight, the recent rainfall combined with lingering dewpoints and light winds will allow for some ground fog across the area. The densest fog will likely be limited to portions of central to north-central Wisconsin. Tuesday will be the main concern for the forecast period. A strong negatively tilted 500mb trough will approach the area, aiding in the rapid development of a surface low pressure system over Iowa and Minnesota. As this fast moving low lifts towards the region, a surface warm front will come northwards to central to east-central Wisconsin. This late morning to afternoon time period will be the first to watch, as most models bring some initial development ahead of the surface warm front. Precipitable water content at this time will be near their climatological max for this time of the year, so very heavy rainfall will be possible, especially in any convection. This initial round may also be accompanied by strong gusty winds but other severe concerns are not expected for this portion of the system. As we get to the late afternoon to evening, the surface low will continue to deepens and shift northwards lifting the warm front further north. At the same time, the attendant cold front will sweep across the region from the west. This will serve as the trigger for a strong organized fast moving round of convection. Given the strong ambient shear but more modest instability (especially off the surface) suspect storm organization will take the form of a quasi-linear system, potentially with some embedded supercells. Any storms that develop will be fast moving, so wind and large hail will be possible with any convection. With low LCL heights and plentiful ambient helicity, tornadogenesis will be possible with any embedded strong storms as well, with the greatest threat likely being along the interaction between the warm front and cold front across central to east-central Wisconsin. In short, all severe weather threats will be of concern Tuesday evening. The main question will be the northerly extent of severe potential, as areas in northern Wisconsin may see fairly limited severe weather while those along or south of a line from Wausau to Green Bay will see the potential for severe weather. This second round should develop to our west and cross the region fairly rapidly, with drier conditions arriving around midnight, plus or minus an hour or two. Long Term...Tuesday Night Through Monday The main focus in the forecast period will be the Tuesday to Tuesday night system. The extended period is relatively quieter. Quiet conditions follow the Tuesday system, with dry conditions expected across the region for the middle of the week. Temperatures during this period will primarily be in the middle 60s to middle 70s. The next chance for active weather will be around the end of the week as a low pressure system cross southern Canada and clips the northern portion of the area. Timing remains uncertain for this system so the overall thunderstorm strength potential remains uncertain at this time. && .AVIATION...for 06Z TAF Issuance Issued at 1117 PM CDT Mon May 20 2024 Conditions ranged from VFR to VLIFR late this evening as fog and low clouds continued to develop. The fog will continue to expand, but will be limited in the west by the cloud debris streaming in from the storms in MN. Where skies stay clear, look for 1/4 and 1/2 mile VSBYs. Thickest fog looks to be over east-central WI, especially MTW, where the heaviest rain fell today. The low clouds and fog will slowly burn off/lift Tuesday morning. Models continue to have slightly different ideas on how things will play out on Tuesday, with at least a couple waves of showers and storms pushing across the area. A round of showers and isolated storms is expected in the later morning and early afternoon associated with the warm front, and possibly what is left from the overnight storm complex. Then, another stronger round (or two) showers and storms is expected as the cold front sweeps east across the area. The storms could produce very strong winds, large hail and heavy rain. Have included two TEMPO groups at each site when the highest chance for thunder exists, but timing will likely need to be tweaked. Winds off the surface will increase ahead of the cold front Tuesday afternoon/evening, with wind shear expected when winds are not gusting at the surface. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....Uhlmann AVIATION.......Bersch