978
FXUS63 KGRR 240549
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
149 AM EDT Tue Jun 24 2025

.KEY MESSAGES...

- Several Chances For Thunderstorms This Week

- Heat Continues This Week

&&

.DISCUSSION...
Issued at 323 PM EDT Mon Jun 23 2025

- Several Chances For Thunderstorms This Week

A line of thunderstorms has already begun to develop across
Wisconsin, which will arrive here mid to late evening. The potential
is there for damaging winds to 60 mph as this line reaches the area
as mid-level dry air has DCAPE values over 1200 J/kg. However, it
will be a narrow window in which the best conditions for strong to
severe storms will exist (roughly 9pm-1am). By the storms arrive
tonight, instability will be decreasing and low-level CIN on the
rise with the loss of daytime heating. CAMs suggest storms will
quickly weaken as they cross the area. The greatest risk across will
be north of Muskegon to Clare, mainly across Mason, Lake, Oceana,
and Osceola Cos which is in line with where the SPC currently has a
slight risk .

The front drifts south through the state Tuesday, eventually
stalling near the state line. This will provide a focus for showers
and storms to develop the next several days. Dewpoints in the 60s to
low 70s will lead moderate instability, mainly across the southern
2/3 of the CWA. However, deep layer shear will be poor under the
large scale ridge, though MCVs and/or outflow boundaries may locally
enhance shear. This may result in isolated strong to severe storms,
with damaging winds as the main risk. The SPC`s marginal risk of
severe storms Tuesday and Wednesday overall aligns with this
thinking. Coverage of showers and storms looks to be most widespread
Wednesday morning, and again Thursday Night/Friday driven by
enhancement of low-level forcing by 700mb shortwaves.

- Heat Continues This Week

Will extend the Heat Advisory for our southern two rows of counties
through Tuesday evening. Dewpoints will be a bit lower than previous
days, and increased cloud cover associated with the front should
keep things a bit cooler near and north of I96. However, lesser
cloud cover and slightly higher dewpoints south of I96 will allow
heat index values to climb to around 100F again Tuesday. Combined
with accumulating heat stress from the last several hot days and
little relief at night, an extension of the advisory is warranted.
Even as heat index values fall into the low to mid 90s north of I96,
it will still be hot and humid areawide and people vulnerable to
heat should continue to take precautions.

While not as hot as the last few days, warm conditions will continue
through the week as large scale ridging persists. Highs in the 80s
and dewpoints in the mid 60s to low 70s will keep muggy conditions
in the forecast with heat indices in the 90s.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 149 AM EDT Tue Jun 24 2025

VFR conditions continue through Tuesday morning. With daytime
heating Tuesday afternoon showers and thunderstorms will be
possible (20 to 50 percent). The best chances will be along and
south of a AZO to LAN line where the best instability is along
with a weak boundary. There is a potential for stronger storms
producing stronger gusts to 40 knots.

Overall southwesterly winds gradually become more westerly with
gusts around 20 knots this afternoon. Winds become light and
variable after OOZ Wednesday.

&&

.MARINE...
Issued at 323 PM EDT Mon Jun 23 2025

Newer iterations of the WaveWatch3 indicate slightly lesser
waveheights the rest of today and this is fairly well corroborated
by available nearshore buoys; however, we do see evidence of
continued elevated waves per webcams at Grand Haven. So, will hold
onto the current Small Craft Advisory and Beach Hazards statement
from Holland north, but we should be able to expire these as
scheduled at 8 PM EDT tonight.

As noted previously, there will be weakening storms approaching from
the northwest tonight and these could persist long enough to affect
the Sable Points region around or shortly after midnight.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Heat Advisory until 8 PM EDT this evening for MIZ064>067-071>074.
MARINE...None.

&&

$$

DISCUSSION...Thomas
AVIATION...RAH
MARINE...TJT