570 FXUS63 KGRR 060708 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 308 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 /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 140 AM EDT Sat Jun 6 2026 Scattered showers and thunderstorms are moving through the area causing various flight conditions from IFR to VFR. Expect conditions to bounce around through 9Z before storms shift south of the area. Heavy rain is likely with any thunderstorm and stronger storms may produce a brief burst of stronger winds 40 to 50 knots. After 12Z conditions are expected to improve to VFR. Isolated storms are possible during the late morning and early afternoon before the front moves through. Confidence in thunderstorms impacting any one airport is low, but have included Prob30s where confidence is a little higher at JXN and LAN. && .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...None. && $$ DISCUSSION...RAH AVIATION...RAH MARINE...RAH

NWS GRR Office Area Forecast Discussion