313
FXUS63 KGRR 051202
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
802 AM EDT Sat Jul 5 2025

.KEY MESSAGES...

- Hot and Humid Today

- Shower and storm chances Saturday night into Sunday night

- Dry Monday and Tuesday; Rain Chances Wednesday-Thursday

&&

.DISCUSSION...
Issued at 356 AM EDT Sat Jul 5 2025

- Hot and Humid Today

Highs in the lower 90s and dew points in the mid-upper 60s are
expected for most locations aside from the immediate Lake Michigan
shore. This will put the heat index toward the mid 90s, so there
is some heat risk for those active outdoors or without air
conditioning.

Expecting diurnal cumulus to bubble up especially in Mid
Michigan. Some models within the HREF are showing a hint of
showers developing around Battle Creek / Lansing this afternoon
as steep lapse rates should allow the clouds about 5,000 to 10,000
feet of vertical development before they reach an equilibrium
with warmer air around 10-15 kft. However, the clouds should be
too warm to glaciate and and so limited rain is expected. Will set
precip probs to about 10 percent.

- Shower and storm chances Saturday night into Sunday night

Showers or storms crossing Lake Michigan may reach the Ludington
area late this evening. Additional scattered showers and
thunderstorms are expected to develop from Sunday morning into
Sunday evening under a 500 mb trough and within broad surface
troughing ahead of a cold front. CAPE may reach a respectable
1500 J/kg and high PW over 1.8 inches which would support taller
storms with efficient downpours, producing a few narrow swaths of
1-2 inch rainfall. Effective deep-layer shear is weak which would
limit organization, but some cells could produce isolated gusts
greater 30-40 mph given the 20-20 knot winds at 1-2 km.

- Dry Monday and Tuesday; Rain Chances Wednesday-Thursday

Once we see the front sink south of the area, dry and cooler weather
should return to the area for Monday. The upper heights drop a bit
as the weekend upper ridge gets flattened well.

Sfc ridging will then dominate over the area Monday through Tuesday.
A flow from the north and east will bring in slightly cooler
temperatures, and much drier air. This will hold over the area until
at least Tuesday evening as the sfc ridge slips east of the area.

Rain chances then look to return to the area for Wednesday and
Thursday, with cooler temperatures holding in over the area. The
upper jet will be dropping in over the Upper Midwest, and allowing a
short wave trough to move over the area. This system will not have
much moisture to work with as we do not see a moist flow set up from
the Gulf ahead of the sfc front. The short wave will mostly act with
diurnal instability to fire a few showers and storms Wed and Thu
afternoons.

There is some uncertainty as to how quick this system moves out
toward the end of next week. We feel it is more likely to move out
by next Friday, but cannot rule out it sticking around a little
longer.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 802 AM EDT Sat Jul 5 2025

Expecting VFR with scattered daytime cumulus development, bases at
or above 4,500 ft. Scattered showers and thunderstorms will tend
to cross Lake Michigan tonight and will may to affect LDM to MKG.

&&

.MARINE...
Issued at 356 AM EDT Sat Jul 5 2025

Breezy south winds today will build waves to 2-4 feet north of
Holland and 3-5 feet north of Whitehall. Initially a low swim risk
at Lake Michigan beaches early today will become more of a
moderate/high swim risk north of Holland as the day goes on.
Scattered thunderstorms affect the lake Saturday night into
Sunday morning. Expecting a moderate-high swim risk throughout
Sunday as winds become more west then north, potentially spreading
the hazardous waves and currents farther south to include South
Haven.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement from noon EDT today through Sunday
     evening for MIZ037-043-050.
     Air Quality Alert until midnight EDT tonight for MIZ050-056-057-
     064-071.
     Beach Hazards Statement from this evening through Sunday evening
     for MIZ056.
MARINE...Small Craft Advisory from 8 PM this evening to 8 PM EDT Sunday
     for LMZ846.
     Small Craft Advisory from noon today to 8 PM EDT Sunday for
     LMZ847>849.

&&

$$

DISCUSSION...CAS/NJJ
AVIATION...CAS
MARINE...CAS