543 FXUS63 KGRB 062344 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 644 PM CDT Mon Sep 6 2021 Updated aviation portion for 00Z TAF issuance .SHORT TERM...Tonight and Tuesday Issued at 313 PM CDT Mon Sep 6 2021 A very quiet and seasonal Labor Day ongoing with some high clouds drifting across the area, along with some daytime cu. Temps were in the upper 60s to middle 70s. For tonight and Tuesday...a quiet evening is expected as most/all of the daytime cu will diminish late this afternoon and evening, as a few high clouds continue to drift across the area. As the evening progresses, a LLJ will strengthen to 40 kts over northern MN, as a shortwave and cold front push southeast into the western Great Lakes. Look for an area of showers/storms expected to develop ahead of these features. Some models have one main area, while others show two separate areas with one associated with the stronger WAA. If the WAA activity gets going, the activity could arrive a little earlier, but the majority of the shower/storms will arrive after midnight, with the bulk of the activity along/north of Hwy 8 overnight into Tuesday morning. Activity along the front is possible across the entire area Tuesday morning, then will exit into Lake Michigan by 18-19z. Additional isolated-scattered showers and possibly a storm will be possible across northern WI as the upper trough swings into the area. As the surface low deepens over northern Lake Superior on Tuesday, gusty winds will develop, with gusts to 30 mph expected. The organized severe weather threat still looks low, as the storms look to be elevated overnight into early Tuesday. However, MUCAPEs will advect into the area as the LLJ moves east, with models ranging from 1500-3000 J/kg. This, along with steep mid- level lapse rates and effective shear of 35-45 kts, will promote some stronger storms with a severe storm also possible near the MI border. This matches with where the Marginal Risk resides. Wet- bulb heights will be running between 8,000-10,000 ft, so hail will be the primary threat in any storm. Wind profiles support some wind gusts as well. The race will be on later Tuesday morning between the advancing front, the weakening cap, and building surface instability. Still a small chance some surface based convection could get going closer to the lakeshore and with decent shear a strong or severe storm would be possible before the front and storms push east into Lake Michigan. PWATs increase to near 1.75" ahead of the front, so locally heavy rainfall will be possible. Lows tonight will be warmer than last night with most spots bottoming out in the 50s to around 60. Highs will be a little tricky on Tuesday as clouds/precip trends could impact how warm parts of the area will get. Lowered highs over the north (mid 60s) as the most widespread showers/clouds are expected, with 70s across the rest of the area. .LONG TERM...Tuesday Night Through Monday Issued at 313 PM CDT Mon Sep 6 2021 Tuesday night through Wednesday night: The front will quickly shift well east of the area Tuesday evening; however, the upper-level trough axis will shift slowly eastward through late Wednesday afternoon. Continued wrap-around moisture along with yet another shortwave passing through the area Wednesday into Wednesday evening, will lead to scattered showers and possibly a few thunderstorms with the cooler air aloft. The best chance for thunderstorms will be Wednesday afternoon during peak heating. 850mb temperatures will likely be cool enough with northwest flow to keep lake effect clouds and possibly rain showers into north-central WI through late Wednesday evening. Otherwise, the increased cloud cover will allow for cooler high temperatures, mainly in the mid 60s to around 70. Overnight lows are forecast to be in the 40s to around 50s. Thursday into Friday, a surface ridge will build across the area, allowing for quiet conditions with precipitation-free conditions. Aloft, upper-level ridging will slowly build across the area. The combination of these features, will lead to warming temperatures, especially into Friday, when temperatures may be near to slightly above normal. Friday night through Saturday: The next low pressure system and associated cold front will approach the area late Friday night before the front passes through the area Saturday. This will lead to increasing chances for showers and thunderstorms with temperatures warming above normal, into the upper 70s. Rest of the extended: Model solutions are generally pointing toward quieter conditions for the end of the weekend. At this point kept the forecast close to the blend of models for that time period. Temperatures are expected to be near normal. && .AVIATION...for 00Z TAF Issuance Issued at 622 PM CDT Mon Sep 6 2021 A strong system is expected to race through the area during the next 24 hours. There is still considerable uncertainty related to the timing, location, and strength of the convection that will accompany it. 20Z SFC analysis indicated the primary cold front was still way back in ND, which raises some doubt as to how quickly the models are sweeping it east across the area tomorrow morning. Opted to make a few minor adjustments to timing (slower) with the 00Z TAF package, but otherwise stuck with the gist of the previous TAF issuance. May make some more substantial changes later this evening if the evolution of the convection becomes clearer. && .GRB WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM.....Bersch LONG TERM......Cooley AVIATION.......Skowronski