227 FXUS63 KGRB 162255 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 555 PM CDT Wed Apr 16 2025 Updated aviation portion for 00Z TAF issuance .KEY MESSAGES... - Showers and thunderstorms return Thursday night and continue through Friday. Some storms Friday afternoon could become strong to severe in the Fox Valley/Lakeshore areas. && .DISCUSSION... Issued at 359 PM CDT Wed Apr 16 2025 High pressure brought sunny skies and dry conditions this afternoon, with low relative humidity leading to elevated fire weather conditions in the grasslands and marshes. High and mid-level clouds were approaching from the southwest. Quiet weather continues through tonight and Thursday morning, with patches of mid-level clouds impacting the area. Lows tonight will range from the upper 20s northeast to the lower to middle 30s elsewhere. A 35-40 kt low-level jet and increasing WAA will bring a chance of showers by mid to late Thursday afternoon, especially in C/NC WI. Elevated instability remains southwest of the region until evening, so have left out any mention of storms at this time. High temperatures should reach the middle 50s to lower 60s in most areas, with cooler readings around 50 near Lake Michigan. An 850 mb warm front will lift north across the forecast area Thursday night, and a surface cold front will edge into the northwest part of the area overnight. Showers and scattered thunderstorms will develop, with the best chance of thunder occurring over the southern half of GRB CWA. Although only modest elevated CAPE is forecast, the arrival of very steep mid-level lapse rates (7-8 C/KM) and strong deep layer shear (50-65 kts) is supportive of at least small hail with the elevated storms. Lows will be in the 40s to around 50. On Friday, the cold front will continue to move slowly southeast during the day, as a weak surface low lifts northeast along the boundary. In addition, a 135 kt jet streak is expected to move into the region, providing strong upper level divergence, especially over the SE part of the forecast area. The strongest instability will also reside over the SE CWA, where MUCAPE of 700-1200 j/kg is expected, along with mid-level lapse rates of 7-7.5 C/KM. Deep layer shear is very strong, roughly 60-75 knots. Agree with SPC`s Marginal risk of severe over the Fox Valley and lakeshore areas, especially as the front moves through during the early to mid afternoon. The risk would be greater if we were not expecting abundant cloud cover and ongoing shower activity. Given the elevated nature of the instability, suspect the main threat will be large hail. Showers and a few lingering storms will diminish Friday evening as the front exits. Highs on Friday will range from around 50 far northwest to the 60s southeast. Generally quiet weather is expected for the rest of the week, with showers possible Sunday night into Monday as a low pressure system tracks SE of the region, and another chance Tuesday night into Wednesday as an occluded front pushes through the area. && .AVIATION...for 00Z TAF Issuance Issued at 549 PM CDT Wed Apr 16 2025 VFR conditions will prevail through Thursday morning. Low level wind shear will develop late tonight into Thursday morning before surface winds increase by late morning. Gust to around 30 knots are possible Thursday afternoon. CIGS are expected to rapidly drop into the MVFR/IFR category late Thursday afternoon into Thursday evening and continue into Friday morning. Showers will be on the increase later Thursday afternoon into Thursday night. The chances of thunderstorms return late Thursday night and continue into Friday. Some stronger storms are possible on Friday across east- central Wisconsin that could produce strong winds and hail. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....Kieckbusch AVIATION.......Eckberg