textproduct: Grand Rapids

KEY MESSAGES

- Multiple Rounds of Showers and Thunderstorms, Warm and Humid

UPDATE

Issued at 1002 PM EDT Mon Aug 31 2026

Current thinking is that chances for thunderstorms overnight (which were already low and confined to the US10 corridor) continue to dwindle. Latest sounding from GRB modified with current surface observations suggests a well capped environment is beginning to form with the loss of nocturnal heating. Many of the CAMs suggested convection being ongoing or at least imminnet, which has failed to materialize. Given capping enhancing from here and the placement of the low- level jet, this appears unlikely as of now to change significantly. The 01/00z HRRR has initialized well and keeps any convection across our northern CWA mainly limited to showers.

Given this, lower debris cloud cover and potentially greater insolation may occur tomorrow. Will let the overnight shift re- evaluate if a heat advisory is needed once the rest of the 01/00z guidance comes in.

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 /00Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 717 PM EDT Mon Aug 31 2026

The band of showers and storms that moved across the terminals a few hours ago have weakened and moved south of the border. Another area of light rain showers moving east across the lake will likely remain north of the terminals.

Some LLWS is possible later this evening as a LLJ moves across the region. Otherwise, MVFR fog is possible overnight due to abundant low level moisture.

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...Beach Hazards Statement until 11 PM EDT this evening for MIZ037- 043-050-056. MARINE...Small Craft Advisory until 11 PM EDT this evening for LMZ846>849.