661 FXUS63 KGRR 061144 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 744 AM EDT Sat Jun 6 2026 .KEY MESSAGES... - Isolated Thunderstorms Possible Today - Increasing Chances for Rain and Thunderstorms Monday into Tuesday - Warm and Humid With Slight Chances (20 percent) for Thunderstorms && .DISCUSSION... Issued at 308 AM EDT Sat Jun 6 2026 - Isolated Thunderstorms Possible Today The line of thunderstorms currently moving through the area will exit by 5am. Instability builds back in during the day with the mean HREF surfaced based CAPE values around 1000 J/kg and shear around 35 knots. Even with these values the HREF members are not excited about thunderstorm chances later this morning and afternoon. Other guidance has also decreased on convection later today. This could be due to the lack of lift in the lower levels, but with 500mb positive vorticity advection and the front moving through, will keep a 20 to 30 percent chance with the best potential east of I-69. - Increasing Chances for Rain and Thunderstorms Monday into Tuesday The upper level ridge builds back in for Sunday, but the shortwave over Texas will weaken the ridge bringing with it rain and thunderstorms for Monday and Tuesday. Heavy rain will be possible with precipitable water values around 2 inches. Currently we are in the day 5 Excessive Rainfall Outlook from WPC. Depending on the evolution of the shortwave, rain and thunderstorms could linger into Wednesday. - Warm and Humid With Slight Chances (20 percent) for Thunderstorms Temperatures gradually warm through next week with the best potential for 90s on Thursday as 925 mb temperatures will be in the 24 to 25 C range. However within the southwest flow and the humid environment with dew points in the 60s and 70s, thunderstorms chances could play a role in how warm we actually get. Still worth monitoring as heat indices could be in the 90s multiple days in a row and may approach the low 100s. && .AVIATION /12Z TAFS THROUGH 12Z SUNDAY/... Issued at 744 AM EDT Sat Jun 6 2026 There is a low chance for precipitation at the terminals now that an area of showers and thunderstorms has exited to south of the forecast area. The biggest forecast challenge will be at MKG where marine fog has resulted in LIFR conditions. Conditions are expected to improve during the day but there is considerable uncertainty regarding the exact timing. Our best guess now is that VFR conditions will be realized by noon coincident with the onset of a lake breeze that will promote mixing of the nearshore marine boundary layer. Elsewhere, predominantly VFR conditions are expected although a brief window of MVFR ceiling restrictions this morning can`t be completely ruled out. && .MARINE... Issued at 308 AM EDT Sat Jun 6 2026 For the rest of today thunderstorm chances are low. Winds will shift more to the northwest with the front moving through this afternoon. High pressure then builds into Sunday with winds and waves remaining below Advisory and Statement levels through next week. Thunderstorms will be likely Monday into Tuesday with lower chances lingering through the rest of the week. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...Dense Fog Advisory until 2 PM EDT this afternoon for LMZ846>849. && $$ DISCUSSION...RAH AVIATION...TJT MARINE...RAH

NWS GRR Office Area Forecast Discussion