241
FXUS63 KGRR 212254
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
654 PM EDT Fri Aug 21 2026
.KEY MESSAGES...
- Scattered showers/thunderstorms today into Saturday
- Cooler and dry Sunday through Tuesday, midweek rain chances
&&
.DISCUSSION...
Issued at 314 PM EDT Fri Aug 21 2026
- Scattered showers/thunderstorms today into Saturday
Scattered thunderstorm cells have developed along an inland
surface trough / confluence zone east of US-131 and will move east
this evening. These are ahead of diminishing convection from
Wisconsin with midlevel MCVs apparent on radar. The storms are in
an area of MLCAPE 500-1000 J/kg. Modeled effective shear is no
more than 20 knots, though it`s possible the MCVs could boost the
shear values somewhat and provide greater longevity to the cells.
Small hail and wind gusts to 40 overall are possible today.
Additional scattered storm cells are likely tonight, with elevated
bases via 850 mb moisture, then may become more surface based as
they move toward Mid Michigan later Saturday. CAPE values will
generally be 500-1500 J/kg and effective shear is likely to remain
no more than 20-25 knots. Lapse rates both at low and mid levels
should be fairly modest during much of this activity which should
also help keep severe wind/hail potential low.
QPF mean is about 0.10 to 0.25, though more realistically, amounts
will be more hit or miss, with a few isolated totals closer to 1
inch possible.
- Cooler and dry Sunday through Tuesday, midweek rain chances
Northwest flow Sunday and Monday will provide slightly cooler,
drier, more comfortable air as the upper-level trough turns cutoff
low over the eastern/northeastern Great Lakes region. A minor
return of moisture and warmer air occurs from late Tue into Wed,
with scattered thunderstorms again possible with the next frontal
wave.
&&
.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 654 PM EDT Fri Aug 21 2026
Scattered showers and isolated thunderstorms are possible over the
next several hours, though coverage is too low for TAF inclusion
of any thunder threat with 10-20% impacts for terminals. Chances
increase later this evening into tonight with a pre-frontal trough
followed by a cold front. Given high variability in short range
model guidance and questions on coverage have maintained previous
PROB30s for all terminals. Winds then increase from the northwest
behind the cold front with gusts to 25 knots expected. The other
concern is high dewpoints favor a period of low clouds and patchy
fog near daybreak, particularly in any thunderstorms. Mainly MVFR
is favored at this time, but IFR cannot be ruled out in
thunderstorms.
&&
.MARINE...
Issued at 314 PM EDT Fri Aug 21 2026
Ongoing Beach Hazards Statement / Small Craft Advisory for near
Big and Little Sable Points through Fri evening is fairly low
confidence given latest data, as south winds 10-15 knots may only
build up 2 to 4 foot waves with a moderate swim risk before
subsiding tonight. Scattered thunderstorms are possible over the
lake tonight with a low chance for gusts to 30 knots.
More likely hazards from wind, waves and currents for this weekend
as north-northwest winds increase behind a cold front. There
remain some differences in the models regarding the strength of
winds at times, but overall, waves should build to 3 to 6 feet at
most beaches later Saturday morning. Then after a slight lull
Saturday evening, winds likely strengthen and waves build again
Saturday night into Sunday.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement until 8 PM EDT this evening for MIZ037-
043.
Beach Hazards Statement from Saturday morning through Sunday
evening for MIZ037-043-050-056-064-071.
MARINE...Small Craft Advisory from 8 AM Saturday to 11 PM EDT Sunday for
LMZ844>849.
Small Craft Advisory until 8 PM EDT this evening for LMZ848-849.
&&
$$
DISCUSSION...CAS
AVIATION...Thomas
MARINE...CAS
NWS GRR Office Area Forecast Discussion
