306
FXUS63 KGRR 311915
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
315 PM EDT Mon Aug 31 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 /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 122 PM EDT Mon Aug 31 2026
Radar shows a band of convection over the lake moving east. This
precipitation is on the leading edge of mid level temperature
advection and is moving into an area with higher instability.
We`ll continue to monitor for additional development.
A LLJ will move overhead tonight resulting in some LLWS during the
late evening and early overnight. Given recent rain, some MVFR fog
is possible toward morning for a few hours.
&&
.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.
&&
$$
DISCUSSION...CAS
AVIATION...04
MARINE...CAS
NWS GRR Office Area Forecast Discussion
