034 FXUS63 KGRR 092346 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 746 PM EDT Mon Jun 9 2025 .KEY MESSAGES... - Round of Thunderstorms this Afternoon and Evening - Additional Thunderstorm Chances Late Week && .DISCUSSION... Issued at 253 PM EDT Mon Jun 9 2025 - Round of Thunderstorms this Afternoon and Evening As daytime instability has increase to around 500-1000 J/kg this afternoon we are already seeing showers and storms develop ahead of the main line currently moving across Lake Michigan. We will also see a core of slightly stronger 850mb winds 30-35 knots move in with the line. Sounding profiles have an inverted V look to them signifying higher cloud bases and drier air at the surface. With the synoptic lift moving in with the upper level low, modest shear, instability, and dry air at the surface some strong to severe storms are possible with winds being the primary threat and hail as the secondary. Once the line of storms over Lake Michigan moves through, dry conditions are largely expected overnight. Some showers may linger toward US-10 overnight. - Additional Thunderstorm Chances Late Week We remain in the northwest flow with a couple weak shortwave troughs moving through Tuesday/Tuesday night and then again Wednesday night into Thursday. The low level jet noses in Tuesday night, but moisture is lacking. Better moisture is present Wednesday night into Thursday with showers and storms expected to continue off an on through the remainder of the week as a boundary stalls over the area. This matches up with the NBM PoPs of 30 to 50 percent. Temperatures during this time will be in the 70s to low 80s with lows in the 50s. Friday looks to be the coolest day of the week with areas north of I-96 potentially remaining in the 60s. && .AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/... Issued at 746 PM EDT Mon Jun 9 2025 Generally high confidence for terminals to remain above IFR thresholds overnight now that thunderstorms have exited the area and because we expect at least some wind to persist overnight. We are seeing a trailing deck of high MVFR ceilings (generally above 4000 ft AGL) that may impact the JXN, LAN, and possibly BTL terminals mainly before 02Z. Winds do remain quite brisk at some locations (including GRR) at the time of this writing, but we expect wind speeds to decrease substantially as we approach sunset and associated stabilization of the boundary layer takes place. Rainfall was scant in coverage overall, but the BTL terminal did get some decent accumulations so there is a non-zero chance for MVFR visibility restrictions in fog there, maybe even brief IFR, if winds manage to decouple. && .MARINE... Issued at 253 PM EDT Mon Jun 9 2025 Scattered thunderstorms this afternoon could bring gusty winds and hail. Once storms pass dry conditions are expected until Wednesday night. Winds may approach small craft advisory right along the shoreline this afternoon, but the colder water temperatures should keep most of these gusts at bay. Winds look to remain below Small Craft Advisory levels and in turn wave heights are expected to be around 3 feet or less through the remainder of the week. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...RAH AVIATION...TJT MARINE...RAH