712 FXUS63 KGRB 210345 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 1045 PM CDT Fri Aug 20 2021 Updated aviation portion for 06Z TAF issuance .SHORT TERM...Tonight and Saturday Issued at 351 PM CDT Fri Aug 20 2021 The main focus from this forecast period is the passing of a weakening cold front on Saturday, which will bring a broken line of showers and possible storms ahead of it. Persistent south/southwest low-level winds will continue to lift warmer air across the area overnight, allowing for fog-free conditions and mild low temperatures mainly in the middle to upper 60s. Meanwhile, clouds and a broken line of showers and storms will move into central and north-central WI after midnight ahead of an approaching cold front. But, the trend continues with the line weakening and decreasing in coverage as it reaches the forecast area. Kept the chance PoPs moving from west to east across the area through late Saturday afternoon as there is some potential for the showers and storms to remain somewhat intact by the time it reaches the eastern half of the forecast area around midday. There is some indication of the cold front slowing down during the afternoon, which could allow for redevelopment in far eastern WI. If anything redevelops, the showers and storms would likely be in the pop-up fashion due to the lack in deep-layer shear paired with marginal instability. Due to the lingering warm air ahead of the cold front, high temperatures will be above normal ranging from the upper 70s to middle 80s. The cold front should exit the region to the east by Saturday evening. .LONG TERM...Saturday Night Through Friday Issued at 351 PM CDT Fri Aug 20 2021 The main forecast concerns in the extended portion of the forecast will be the potential for showers and thunderstorms throughout the week. Temperatures will start out well above normal before cooling toward normal for the end of the work week. Saturday night through Sunday: High pressure will build across the area as the cold front shifts east across Lower Michigan. This will allow for quiet weather under partly cloudy skies. Otherwise, overnight lows are expected to be in the mid to upper 40s central/north-central to the 50s elsewhere. Sunday night through Monday: The surface ridge is expected to shift off to the east of the area Sunday night as a low pressure system moves from southern Manitoba to near James Bay by Monday afternoon. This will drag weak surface trough/cold front through northeast Wisconsin from west to east. Aloft, a weakening shortwave is expected to lift near or just north of the UP/WI border. Enough instability (around 1000J/kg) will be in place to touch off a few showers and thunderstorms with the weak forcing along the surface trough. Still looks like most places will remain dry, but still worth keeping small chances for showers and thunderstorms through late morning or early afternoon. Shear values are only progged to be around 20 to 25kts, so if any stronger storms develop, they would likely remain pulse-type thunderstorms with limited chances for severe weather. Overnight lows are expected to be in the mid to upper 50s to around 60. High temperatures are forecast to be in the mid 80s. Monday night through Wednesday: A warm front is expected to lift northward toward northern Wisconsin late Monday night through the day Tuesday. This will lead to increasing cloud cover on WAA and increase moisture into the area. As isentropic upglide increases, expected showers and thunderstorms to develop, especially late Tuesday morning into the afternoon. Tuesday night into Wednesday, a surface low and associated cold front are expected to pass through the area, bringing an even greater chance for showers and thunderstorms. Instability is expected to increase into the 1000- 2000 J/kg range along with deep-layer shear values increasing to around 25 to 30 kts. This would indicate an increasing potential for strong to severe thunderstorms; however, the exact details (timing of the front, exact amt of instability/shear) will have to be ironed out before overall threat can be determined. Overnight lows are expected to be in the upper 50s to mid 60s. High temperatures are forecast to be in the mid to upper 80s Tuesday before cooling into the upper 70s to low 80s Wednesday. Rest of the extended: Models differ on the exact timing and details of the next system to impact the area toward the end of the week into the next weekend; however, it does look to be unsettled through at least Friday. Temperatures for that time period will likely trend a bit cooler with most locations remaining in the 70s for high temperatures. && .AVIATION...for 06Z TAF Issuance Issued at 1045 PM CDT Fri Aug 20 2021 After a period of mostly clear skies, clouds will return after midnight spreading from west to east across the area ahead of a cold front. The front will push a broken line of showers, and possibly a few storms, from west to east on Saturday. Low confidence whether storms from Minnesota will make it into the central WI taf sites. But in general, rain chances will gradually decrease as the front moves east. Highest chances of rain will occur over north- central WI, where a brief period of IFR cigs is possible where rain occurs. Further east, continued to use the prob30 group for thunderstorms over the eastern WI taf sites for a few hour window Saturday afternoon due to uncertainty about coverage. LLWS is expected to develop around midnight and continue for a few hours into early Saturday morning, but should only impact the central and north- central WI TAF sites. Once the front clears the region by late afternoon or early evening, mostly clear skies and good flying weather will return to northeast WI. && .GRB WATCHES/WARNINGS/ADVISORIES... Beach Hazards Statement from 10 AM CDT Saturday through Saturday evening for WIZ022. && $$ SHORT TERM.....Hykin LONG TERM......Cooley AVIATION.......MPC