689 FXUS63 KGRR 010548 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 148 AM EDT Tue Sep 1 2026 .KEY MESSAGES... - Multiple Rounds of Showers and Thunderstorms, Warm and Humid && .DISCUSSION... Issued at 315 PM EDT Mon Aug 31 2026 - Multiple Rounds of Showers and Thunderstorms, Warm and Humid We remain on the northern edge of a heat dome and in a "ring of fire" pattern around the SE CONUS high through at least Wednesday. Predictability has been fairly low in this pattern, with varied model solutions regarding thunderstorm development, as so far the last few days the storms have been based on weak ripples in the mid and upper-level flow and moisture advection at 800-700 mb. Storms this afternoon are likely not to be surface based, and downdraft CAPE is also meager, but they could mix down some 30 mph gusts locally. Heat advisories were considered mainly for near I-94 as NBM highs in the lower 90s and dew points in the lower 70s Tuesday and Wednesday may push the heat index above 100. However, uncertainty in cloud cover and thunderstorm potential leans us toward holding off for now. Thunderstorm potential is very iffy on Tuesday and most models are not enthusiastic in convective development. A plume of higher CAPE and adequate deep-layer shear overhead on Tuesday does support a marginal risk of severe winds or hail if isolated thunderstorms do develop. It`s possible for surface-based storms to develop over Mid/Central Michigan later in the day, or for an upstream complex to cross Lake Michigan, per a few models. But confidence is low, and ended up broadbrushing 20-30 percent chances for precip over much of the area. A somewhat more pronounced shortwave may eject out of the western CONUS and could lead to more thunderstorms, perhaps an MCS, at some time during the day Wednesday, with another marginal or slight risk for severe winds or hail. Despite the worst of the heat getting nudged south by an amplifying ridge/trough pattern over the Central to Northeast US after Wednesday, the majority of ECE members have been retaining MUCAPE over the area through at least Thursday and Friday. The 12z deterministic ECMWF has not been nearly as amplified with the ridge/trough also. This may support additional chances for elevated thunderstorms later in the week, more so favored over southwest Michigan. && .AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 148 AM EDT Tue Sep 1 2026 VFR weather prevails across the area at 06Z with mainly clear skies and no restrictions to visibility currently. Winds aloft will subside considerably in the hours that remain through sunrise. The lowering in wind speeds aloft may allow for some fog to develop around sunrise or in the 11z-13z time frame. Have included this at the western TAF sites. At this point only expecting some MVFR fog. Otherwise expecting VFR weather with some scattered to potentially broken cumulus development today during the heat of the afternoon. Bases will be VFR up around 5,000 feet. Above that some cirrus will continue to advect in from the west with bases at or above 20,000 feet. The item to keep an eye on today is the small potential for showers and thunderstorms this afternoon and evening. At this point feel the threat is too small to include in the TAFs, generally less than 10 percent. If confidence increases we will include going forward, but for now we have dry TAFs. && .MARINE... Issued at 315 PM EDT Mon Aug 31 2026 2 to 5 ft waves have built up between Holland and Ludington as expected this afternoon. South-southwest winds will gradually relax this evening and the wave fields should diminish enough to let the Beach Hazards Statement and Small Craft Advisory expire at 11 PM. Overall weaker winds and lower waves are expected Tuesday and Wednesday, but the main hazard those days will be a chance for scattered thunderstorms to cross the lake once in a while. Any storms Tue or Wed that cross the lake could be capable of stronger wind gusts over 34 knots. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...CAS AVIATION...Duke MARINE...CAS

NWS GRR Office Area Forecast Discussion