395 FXUS63 KGRB 090353 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 1053 PM CDT Tue Jul 8 2025 Updated aviation portion for 06Z TAF issuance .KEY MESSAGES... - Showers/storms likely (60-80% chance) late Friday into Saturday. Confidence in severe storms is low, but locally heavy rain may occur. && .DISCUSSION... Issued at 213 PM CDT Tue Jul 8 2025 Scattered Storms Through This Evening... Broad mid-level trough will pass across the northern Great Lakes this afternoon into early evening. Overall, limited synoptic forcing and modest low-level convergence should tend to keep convection isolated to scattered and fairly disorganized, with the higher chances along the WI/MI border. Mid-level lapse rates should be rather weak, but RAP/SPC mesoanalysis suggest MLCAPE reaching 1000-1500 J/kg across eastern Wisconsin this afternoon. With 30-40 kts of effective bulk shear, hail or gusty winds could not be ruled out with any more persistent cores, especially across far northeast Wisconsin where temps aloft are cooler and forcing from the shortwave may be a bit stronger, but the overall threat looks quite limited. SPC did add a marginal (level 1 of 5) risk for severe storms for a small area of northeast Wisconsin to account for this risk. Storms may persist into the evening before diminishing as instability wanes. Mid Week into Early Next Week... Surface ridging will provide dry weather for the mid-week period. The next period of focus for more impactful weather comes Friday into Saturday as a shortwave trough emerging from the central Rockies interacts with a broader trough approaching from the northern plains. Rich moisture will be advected northward in advance of this system with precipitable water values forecast to exceed the 90th percentile relative to climo, based on the NAEFS. Although synoptic and mesoscale details remain unclear, the environment would support the potential for locally heavy rainfall. Right now, the NBM shows the footprint of highest probabilities for at least 1" of rain during this time (30-50%) across parts of Minnesota and western Wisconsin. The degree of destabilization remains unclear on Friday, and with relatively weak deep layer wind shear expected, the overall severe weather threat looks rather low for now, with the various machine-learning outputs showing general 5-15% probabilities for severe weather across the area on Friday. The timing of the wave could impact rain/storm chances heading through Saturday. Otherwise, a typical mid-July weather pattern will continue late this weekend into early next week with quasi-zonal flow across the northern tier of states and any showers/storms tied to lower predictability shortwave troughs. No clear precipitation signal is evident at this time. Temps generally look seasonable over the next week with a slow climb for mid to late week along with increasing humidity levels late this week. && .AVIATION...for 06Z TAF Issuance Issued at 1052 PM CDT Tue Jul 8 2025 Patchy fog is possible after midnight mainly over north-central WI and near Lake Michigan. Have included mentions of VSBY reductions at RHI and MTW. Otherwise, sct-bkn IFR/MVFR stratus will settle across all but central WI. The lower CIGS lift on Wednesday morning, but could still remain MVFR Fox Valley to the lakeshore. By afternoon, all terminals will see scattered VFR cu. Winds will be light through the entire TAF period. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....JM AVIATION.......JLA