295 FXUS63 KGRB 302343 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 643 PM CDT Fri Jul 30 2021 Updated aviation portion for 00Z TAF issuance .SHORT TERM...Tonight and Saturday Issued at 253 PM CDT Fri Jul 30 2021 Main forecast issue will be extent/potential severity of thunderstorms on Saturday. The 19Z MSAS surface analysis showed an area of high pressure that stretched from eastern Lake Superior southwest through eastern WI into northwest IL. A cold front was located from southern Manitoba through northwest ND. Visible satellite imagery indicated a large band of clouds/scattered showers and storms from SD east- southeast into the western Great Lakes region associated with a weak system. The high pressure will slowly shift east this evening, allowing for the cold front to approach northern sections of the Great Lakes toward daybreak. Accompanying the cold front will be an embedded mid-level shortwave trough moving southeast within the broad northwest flow aloft. Have kept a small chance pop over far northern WI after midnight, otherwise partly cloudy skies and hazy conditions to exist with smoke from western wildfires drifting overhead. Min temperatures to mainly be in the middle 50s to around 60 degrees. The cold front and shortwave trough are forecast to push southeast through the forecast area Saturday afternoon (early to mid- afternoon north/late afternoon-early evening south). The air mass over the region will be moderately unstable with SBCAPES of 1000- 1500 J/KG, 0-6km bulk shear of 30-40 knots and mid-level lapse rates of 5.5 to 6.0 C/KM. Anticipate scattered showers and thunderstorms to move across northern WI late Saturday morning into Saturday afternoon, then spread across central and east- central WI Saturday afternoon. Some of these storms may become strong to locally severe across central/east-central WI where stronger instability to be present. Marginally large hail and gusty winds would be the primary threat. Max temperatures on Saturday to be in the middle to upper 70s north/near Lake MI, upper 70s to around 80 degrees south. .LONG TERM...Saturday Night Through Friday Issued at 253 PM CDT Fri Jul 30 2021 Northwest upper flow and surface high pressure will make for mainly cool and dry weather Sunday through Tuesday. Temperatures should be 5 to 10 degrees below normal with comfortable relative humidity. A few weak upper troughs will move around the upper ridge over the Rockies and Plains states during the middle of the week, with a chance of afternoon showers or thunderstorms. Temperatures will be close to normal. Upper heights will rise towards the end of the week, as the upper ridge slowly edges east. Southerly low level flow will bring warmer and more humid air into the region, though warming mid level temperatures may inhibit convection most of the time. Highs will be 5 to 10 degrees above normal by Saturday. && .AVIATION...for 00Z TAF Issuance Issued at 633 PM CDT Fri Jul 30 2021 The primary aviation weather concern will be the impact of a cold front dropping south across the area tomorrow. Moisture will be limited and forcing rather weak, so the timing of convection associated with the front is somewhat uncertain. Opted to keep the mention of thunder close to the front, which means it won't make it into the KOSH/KMTW TAF sites until the next issuance. A secondary issue is the impact of smoke from western wildfires. Relied heavily on HRRR output for this aspect of the TAFs. Alluded to the smoke aloft with a SCT skycon. The near SFC smoke fcst indicates the highest concentrations will occur late tonight into mid-morning Saturday, went with 4-6SM vsbys for this period. && .GRB WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM.....Kallas LONG TERM......RDM AVIATION.......Skowronski