866 FXUS63 KGRR 042350 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 750 PM EDT Fri Sep 4 2026 .KEY MESSAGES... - Showers and Thunderstorms This Evening - Drying out and cooling off this Weekend - Rain Possible Tuesday && .DISCUSSION... Issued at 318 PM EDT Fri Sep 4 2026 - Showers and Thunderstorms This Evening The radar this afternoon shows scattered thunderstorms in an area of isentropic ascent and moisture advection from southern Wisconsin into southwest Lower Michigan. The convective-allowing models such as the hi-res ARW and FV3 show the storms across southern Wisconsin moving east-southeast this evening and traversing the southern half of the forecast area. This is reflected in the forecast, although tweaks may be needed of course thanks to the inherent uncertainty in modeling convection that we have seen the past several days. - Drying out and cooling off this Weekend A developing Omega block across the CONUS this weekend results as the central U.S. heat dome is bookended by cut off lows across the NE and NW CONUS. This lowers heights across the central Great Lakes and allows surface high pressure to build in from the northeast with lower temperatures and dew points and a very fine Labor Day weekend from Saturday through Monday. In face, morning lows on Sunday and Monday could be in the upper 40s to lower 50s across the northern half of the forecast area. - Rain Possible Tuesday into Wednesday The surface high retreats east eastward by Tuesday as the Omega block breaks down. The low across the Pacific NW kicks east and flattens the upper high, with surface low pressure tracking across the northern Great Lakes. Return flow of moisture and a surface warm front should kick off some showers and thunderstorms late Tuesday into Wednesday. Another round of storms will be possible as a cold front moves through late Wednesday. && .AVIATION /00Z TAFS THROUGH 00Z SUNDAY/... Issued at 750 PM EDT Fri Sep 4 2026 Last several runs of the HRRR and also this afternoon`s RRFS models develop thunderstorm cells either vicinity or SW of AZO and BTL between 02 and 07 Z, so have gone with prob30 thunderstorm for now. Can`t completely rule out a rogue shower or storm cell affecting the other TAF sites to the north and east during that time frame. Otherwise, IFR ceilings and/or visibility become likely after 06 Z through about 13 Z, improving to MVFR during the late morning. && .MARINE... Issued at 318 PM EDT Fri Sep 4 2026 Showers and thunderstorms could bring brief heavy rain and gusty winds from Grand Haven to South Haven this evening, then fair weather with light offshore winds, generally less than 15 knots, can be expected for Saturday through Monday. High pressure will move east on Tuesday and winds will be on the increase, with a Small Craft Advisory possible. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...Ostuno AVIATION...CAS MARINE...Ostuno

NWS GRR Office Area Forecast Discussion