119 FXUS63 KGRB 281956 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 256 PM CDT Wed Aug 28 2019 Forecast discussion for routine afternoon forecast issuance .SHORT TERM...Tonight and Thursday Issued at 256 PM CDT Wed Aug 28 2019 The main forecast challenge for the short term is timing out the passage of the cold front on Thursday, and assessing the severe thunderstorm potential corresponding to the frontal passage. Today, gusty winds are expected to continue through the afternoon and evening as a tight pressure gradient lingers across the region with the passage of an upper level trof. By the late afternoon to evening, this initial trof is expected to move out east, allowing high pressure to build back in for the overnight. This will bring clearing skies overnight, along with calmer winds. Overnight low temperatures are expected to be in the middle 40s to lower 50s. Thursday brings in the main focus of the short term, as a cold front moves into the region. The front will be accompanied by an upper level shortwave and the right entrance region of a relatively strong upper level jet (100-110 knots). Additional upper level support is also present, with strong winds in the mid to upper levels and bulk shear around 50-60 knots, both of which will support organization of any developing storms. The main things lacking for more widespread severe weather in the region, are instability and moisture. Therefore, the main thing to keep an eye on will be the weak WAA tonight, ahead of the cold front and how much moisture can get back into the region by Thursday morning, before the front moves through. The GFS and ECMWF both keep CAPE within the 500-1000 J/kg range through the late afternoon, with a more stable mid layer ahead of the front. The NAM brings in much higher instability by the late day, in excess of 1500 J/kg. Given that the front is still further south than previously forecast, which would delay moisture tonight, currently suspect that the NAM is a bit exaggerated. That said, support for some storms does exist, and with the ample upper level support, some scattered strong to severe storms are possible, especially later in the day with more diurnal heating. Given the potential for diurnal heating to increase the severe threat later in the event, SPC has increased the marginal risk area to encompass more of northeastern Wisconsin than the previous issuance. A slight risk area also stops just south of the Fox Valley. High temperatures tomorrow will range from the upper 60s in the north, to the lower 80s in the Fox Valley. .LONG TERM...Thursday Night Through Wednesday Issued at 256 PM CDT Wed Aug 28 2019 Showers and thunderstorms should have exited eastern Wisconsin by Thursday evening, with clearing skies to follow. A surface high builds in for Friday and the Labor Day weekend, though Friday night and Saturday could turn out to be cloudy as a shortwave trough moves through the northwest upper flow. Some sprinkles or light showers are not out of the question south of highway 10 Saturday, but left them out of the forecast. Temperatures should be a few degrees below normal for this time of the year. An upper trough and surface cold front will bring another chance of showers and thunderstorms Monday night and Tuesday. && .AVIATION...for 18Z TAF Issuance Issued at 153 PM CDT Wed Aug 28 2019 Gusty winds through the afternoon will be the main aviation concern for today, with some gusts up to 20 to 25 knots. VFR conditions are otherwise expected, as clouds slowly lift through the day and skies clear from the western to eastern TAF sites this evening and tonight. A front is expected to sweep through the region starting this morning, bringing a round of showers and thunderstorms through the region tomorrow. By the end of the TAF period, the only areas impacted by active weather are expected to be RHI and potentially AUW and CWA, depending on the speed of the front. && .GRB WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM.....Uhlmann LONG TERM......RDM AVIATION.......Uhlmann