


Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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853 FXUS63 KGRB 200353 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 1053 PM CDT Tue Aug 19 2025 Updated aviation portion for 06Z TAF issuance .KEY MESSAGES... - Patchy dense fog overnight tonight through daybreak on Wednesday, especially central and north-central Wisconsin. - Isolated showers are possible at times through Wednesday. The rest of the week will be dry with the next chance for showers and thunderstorms Friday into Friday night. Severe storms are not expected. - Temperatures will be around normal for much of the upcoming week, with the potential for well below normal temperatures late in the weekend into early next week. && .DISCUSSION... Issued at 211 PM CDT Tue Aug 19 2025 Low amplitude shortwave trough in northwest flow along with ongoing cold air advection will result in small chances for showers through Wednesday. High pressure centered over northern MN and western Lake Superior through Wednesday with low pressure crossing the lower Great Lakes will lead to general northeast low-level winds, with convergence maximized near bay of Green Bay and Lake Michigan. It will be in this zone, where the shower chances will be maximized on Wednesday. Rainfall amounts will be very light, well under 0.25 inch through Wednesday. Given the cooler air flowing across the lakes (+12c at 850mb/5kft), took a glace at potential lake effect processes aiding in the showers, but even with water temps on the lake and the bay around 68-72f (20-21c), delta t/s stay below threshold of 13c which is typically what is needed to see even a weaker lake response. This also keeps us out of any range for potential waterspouts, for now. Other issue through Wednesday will be patchy dense fog late tonight into early Wednesday. Using the HREF data, highest risk of visibility less than 1 mile (30-60%) is located over central and north-central WI. Added mention of patchy dense fog to the HWO. Temps tonight will drop into the 50s north-central into far northeast WI. Highs on Tuesday will mostly rise to the middle to upper 70s. Looking ahead, after a couple days of dry weather later Wed through Thu thanks to Canadian high pressure, approaching cold front brings next chance of showers and storms across the region on Friday. Instability and shear shown by LREF could support isolated strong storm if this fropa occurs during max heating on Friday afternoon, but severe storms are not expected. Behind the front, next weekend looks more fall-like with highs by next Sunday perhaps not even reaching 70. Skies will partly to mostly cloudy with cu and stratocu and it may be breezy at times. Forecast currently will carry small chance of showers on Sunday, especially north and northeast. Pattern would suggest that later forecasts may end up showing higher chance for showers especially Saturday over the north and on Sunday for all areas, along with an increase in cloud cover. Further increase in the showers may be due to lake effect as 850mb temps bottom out at 5-6c. The taste of fall will last through early next week. && .AVIATION...for 06Z TAF Issuance Issued at 1053 PM CDT Tue Aug 19 2025 LIFR/IFR clouds are forecast to spread southwest across the area late this evening and overnight, with some MVFR ceilings likely prevailing over eastern WI. Fog is also expected to develop tonight as winds decrease and enough low-level moisture will remain in place. Mainly IFR/MVFR VSBYs are expected, with some LIFR VSBYs possible in central to north-central WI, where skies will remain clear longer. Some sprinkles or light showers will be possible at times overnight into Wednesday, but should not create any worse flying conditions than the lower clouds and fog. On Wednesday, once the fog lifts, expect lower ceilings to persist early in the day, with a slow improvement through the day as conditions improve to MVFR/VFR. Fog will again be possible Wednesday night into Thursday morning, but likely after 06z Thursday. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....JLA AVIATION.......Bersch