386 FXUS63 KGRR 051031 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 631 AM EDT Wed Aug 5 2026 .KEY MESSAGES... - Periods of Rain and Thunderstorms Into Next Week && .DISCUSSION... Issued at 205 AM EDT Wed Aug 5 2026 - Periods of Rain and Thunderstorms Into Next Week The moisture and instability axis with the front currently extends from north central IL into the eastern UP. This is where scattered showers and a few thunderstorms have developed over the past few hours. This axis will slowly shift east into western Michigan this morning. MUCAPE values around 500 to 1000 J/kg will advect into the area throughout the day as well continuing the potential for thunder. Not expecting any severe storms with shear around 20 to 30 knots. However precipitable water values approaching 2 inches and the slow moving front could result in training over the same area creating an environment where some spots could see higher rainfall amounts in the 1-3 inch range. Overall trends for these higher amounts have decreased slightly, but the HREF still shows a signal. A lull in showers and thunderstorms is possible this afternoon before we see another surge of positive vorticity advection move in this evening. Instability drops off around 11pm with scattered showers likely continuing across much of the area overnight. Showers and thunderstorms will likely be focused along and south of a Holland to Alma line during the day Thursday. Instability on the HREF picks up a little higher than today with values around 1000 to 1500 J/kg. Could see more of a diurnal trend with thunderstorm activity where chances become more likely during the afternoon and then drop off as we get closer to sunset. After Thursday the pattern becomes more uncertain as we remain in a broad upper level trough with the potential for multiple shortwaves to move through the region. Each shortwave will bring chances (20 to 40 percent) for showers and thunderstorms. Not any one day looks to be a washout as these shortwaves will quickly move through. Either way, keep an eye on the forecast if you have any outdoor plans as timing will likely change as we get closer. && .AVIATION /12Z TAFS THROUGH 12Z THURSDAY/... Issued at 631 AM EDT Wed Aug 5 2026 A lull in the rain showers has developed with dry conditions likely until late this morning when showers and thunderstorms redevelop. Another lull is possible during the late afternoon with another round moving in between 00-06Z Thursday and lingering into Thursday. Localized heavy rain is possible with heavy rainfall rates and accumulations of 1 to 3 inches. Reduced visibilities will be possible with any shower or storm. MVFR ceilings will slowly move in this evening and overnight. Showers and storms may bring brief periods of MVFR conditions. Fog may also develop as showers exit the area or taper off overnight. && .MARINE... Issued at 205 AM EDT Wed Aug 5 2026 Scattered showers and a few thunderstorms are expected through tonight and may linger south of Holland into Thursday. Lower visibilities will be possible within any shower or thunderstorm. No severe thunderstorms are expected. Largely southwest winds around 5 to 15 knots are expected today before becoming more northerly Thursday. Southwest winds return Friday before becoming westerly Saturday. Periods of showers and thunderstorms exist this weekend into next week, although there is uncertainty with the exact timeframes for showers or storms to occur. Overall winds and waves are expected to remain below Small Craft Advisory and Beach Hazard Statement levels. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...RAH AVIATION...RAH MARINE...RAH

NWS GRR Office Area Forecast Discussion