886
FXUS63 KGRR 060832
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
432 AM EDT Sun Jul 6 2025

.KEY MESSAGES...

- Showers and Thunderstorms Likely Today

- Chances (20 to 40 percent) for Showers and Storms Mid-Late Week

&&

.DISCUSSION...
Issued at 405 AM EDT Sun Jul 6 2025

- Showers and Thunderstorms Likely Today

Localized 40-60 mph wind gusts and several narrow swaths of 1 to 3
inch rain totals are possible today as scattered thunderstorms
develop in a moist atmosphere with PW around 2 inches. Rain
showers and perhaps some thunderstorms are favored to develop this
morning in the vicinity and northwest of a line Holland to Grand
Rapids to Mount Pleasant as a wave along the front passes through
with CAPE less than 1000 J/kg. Instability increases during the
afternoon with surface heating and arrival of a 500 mb trough,
reaching about 1500 J/kg to the east of the Holland-GR-Mt Pleasant
line. Broad surface troughing and general low-level convergence
ahead of the cold front will help scattered thunderstorms develop
throughout the afternoon. The storms will produce very efficient
downpours given the high-PW atmosphere today. Effective deep-layer
shear is marginal but could reach 20-30 knots, so some limited
organization could occur with a few better hail cores. The fallout
of any hail cores that pulse up and the relatively colder
downdrafts that result raises the possibility of wet microbursts
and locally gusty winds.

- Chances (20 to 40 percent) for Showers and Storms Mid-Late Week

Overall ensemble guidance shows several weak shortwave troughs that
move through at times next week. There is variability overall in
both the timing and depth of these shortwave troughs. Either way
with the moisture in place any disturbance could spark off showers
and thunderstorms. Given the ensembles and the overall timing, feel
the the NBM PoPs (20 to 40 percent) are reasonable mainly during the
Tuesday night into Wednesday, Thursday, and Friday timeframes.
Diurnal heating could help bump chances slightly during the
afternoon and early evening hours. With this set up though, no one
day looks like a washout.

Additionally, temperatures will be more seasonable with highs in the
80s and lows in the upper 50s to mid 60s.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 240 AM EDT Sun Jul 6 2025

MVFR to IFR ceilings from the north will spread into MKG this
morning. MVFR ceilings will gradually spread southeastward,
reaching GRR later in the morning (approximately 15Z) and JXN by
no later than this evening (approximately 02Z), per a consensus of
short-term models. But flight category is liable to drop to
temporary IFR sooner than ceilings would suggest due to moderate-
heavy rain showers and scattered thunderstorms. These should
affect MKG and GRR vicinity this morning then GRR vicinity and
many areas south and east of GRR this afternoon.

&&

.MARINE...
Issued at 432 AM EDT Sun Jul 6 2025

Southwest winds over Lake Michigan veer northwest then north as
the day goes on. The veering winds will occur earlier in the day
the farther north you are. Generally, waves will be 2 to 4 feet
with a moderate swim risk at many beaches, but some beaches and
nearshore areas (particularly between Manistee and Whitehall) could
reach 3 to 5 feet with 25 knot gusts at times, a hazard for
swimmers and small craft. Scattered thunderstorms could also
develop over the lake today.

Updated to extend hazard end time past sunset.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement through this evening for MIZ037-043-050-
     056.
MARINE...Small Craft Advisory until 11 PM EDT this evening for LMZ846>849.

&&

$$

DISCUSSION...CAS/RAH
AVIATION...CAS
MARINE...CAS