900 FXUS63 KGRB 081715 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 1215 PM CDT Fri Oct 8 2021 Updated aviation portion for 18Z TAF issuance .SHORT TERM...Today...Tonight...and Saturday Issued at 342 AM CDT Fri Oct 8 2021 WV imagery showed an upper low over northern IL, with multiple short-wave troughs wrapping around it. One weakening deformation zone (and associated showers) was slowly lifting north out of WI, while another short-wave and pocket of low-level moisture convergence was generating a compact area of showers and embedded thunderstorms over southeast WI and southern Lake Michigan. These showers will likely move into the southeast part of GRB CWA within the next hour or two. Widespread low stratus and areas of fog were observed across the forecast area. The previously-mentioned area of showers will likely impact parts of the Fox Valley and lakeshore areas early this morning before waning. However, as the upper level low drifts northeast, and moves toward east central WI this afternoon, the associated lift will combine with CAPE of 500-800 j/kg to produce numerous showers and a few thunderstorms in the Fox Valley and parts of northeast WI. Expect the shower activity to be scattered elsewhere across the forecast area, with overcast skies prevailing. High temperatures should reach 65 to 70 degrees. The short-wave will continue to shift northeast tonight, with scattered light showers gradually ending from southwest to northeast. Expect areas of fog to redevelop overnight, with low temperatures only dropping into the middle to upper 50s. On Saturday, an upper level ridge will keep the region dry, and may break up the cloud cover enough for some brief periods of sunshine during the afternoon. High temperatures should range from the upper 60s to middle 70s; warmest in central WI. .LONG TERM...Saturday Night Through Thursday Issued at 342 AM CDT Fri Oct 8 2021 An active setup in the long term forecast due to broad southwest flow and several waves/lows moving towards or near the state over the next week. Main focus is on precip potential and timing. Saturday night through Sunday night...A low pressure system will track from the Northern Plains to just north of Lake Superior. Ahead of this system LL warm and moist air advection will stream into Wisconsin, resulting in pwats around 1.0 to 1.5 inches, which is 200-percent of normal for this time of year. Additionally, the LFQ of an upper jet will provide lift. Even with all this, medium range models are not overly enthusiastic with QPF and precip potential across the area, focusing closer to the low center and stronger dynamics. Warm advection around 850mb will also create a strong capping inversion which could suppress development. If the cap is overcome, instability ranges anywhere from a couple hundred J/kg, to 1200 J/kg across far northern WI, along with steep mid- level lapse rates of 7.5 to 8.0 C/km. SPC did include northern WI in the Day 3 Marginal Risk category, so this time period warrants some watching for a few strong thunderstorms, mainly Sunday afternoon, but confidence is low at this time. Monday and Tuesday...Just as the Sunday system clears out late Sunday night/Monday morning, another one rapidly moves from the Southern Plains towards Lake Michigan. This will keep a chance of showers in the forecast from Monday into midday Tuesday. Isolated thunder is possible at times, but instability is very limited by this time. Wednesday through Friday...Models are in decent agreement showing a dry period from late Tuesday through at least midday Wednesday. Then, another system is progged to eject out of the Rockies and move across the Plains taking a north/northeast track towards Manitoba or Ontario, differences arise this far out. Regardless, a tightening pressure gradient could bring some windier conditions for Wednesday into Thursday, and the system itself will bring rain chances from late Wednesday through Thursday night. Specific details will need refinement as the time period gets closer. Temperatures...Minor tweaks to temperatures from the previous forecast with above normal readings expected through the week, especially with overnight lows. Some record high minimum temperatures could be at jeopardy early in the week. && .AVIATION...for 18Z TAF Issuance Issued at 1214 PM CDT Fri Oct 8 2021 An upper trough lifting slowly northeast across the region will produce scattered showers and isolated thunderstorms this afternoon and evening, with only a slight chance of showers later tonight and Saturday. Abundant low level moisture will make for low clouds, patchy fog and IFR conditions late tonight through around 15z Saturday, with VFR conditions by afternoon. Surface wind speeds will remain light. && .GRB WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM.....Kieckbusch LONG TERM......KLJ AVIATION.......RDM