601
FXUS63 KGRR 061804
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
204 PM 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 /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 205 PM EDT Sun Jul 6 2025

Storms have begun to form with scattered showers and storms
expected to temporary drop vsbys and cigs to IFR from 18Z to 00Z.
 Expect scattered convection between 18 to 22Z with more organized
storms as the front moves through between 20Z to 00Z. There is
still some question on timing, hence the overlap in times above.
TAF sites that could see the lines of storms will be LAN, BTL, AZO
and JXN. However if it forms further west AZO and GRR could see
another round of storms late this afternoon. Have adjusted this in
the TAFS.
 The cold front should exit shortly after 00Z with some clearing
in its wake. Ceilings will deteriorate throughout the night and
any areas that received heavy rain could see some patchy fog.
Expect IFR cigs and possibly vsbys overnight between 05Z to 14Z at
LAN, JXN, BTL. MVFR cigs with periods of IFR are possible at GRR
and AZO. MKG could see some showers between 18Z to 22Z but to a
lesser extent in relation to the other TAF sites.
 Any reducing cigs and vsbys overnight will slowly improve Monday
between 14Z to 17Z west to east.

&&

.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 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/RAH
AVIATION...CAS/Ceru
MARINE...CAS