698
FXUS63 KGRR 022317
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
717 PM EDT Wed Jul 2 2025

.KEY MESSAGES...

- Scattered Storms Possible Through Friday

- Showers and Storms Possible Saturday Night into Sunday

- Warming Late Week Then Slight Cooling Next Week

&&

.DISCUSSION...
Issued at 244 PM EDT Wed Jul 2 2025

- Scattered Storms Possible Through Friday

Convergence across the eastern portions of the CWA combined with
assistance from a mid-level wave should lead to widely scattered
showers and storms near US127 this afternoon. Then tonight, a weak
front dropping south from the Upper Peninsula will lead to
additional scattered showers and storms. The best chance for any
showers and storms tonight will be north of M46, especially areas
west of US131. There is a low chance this afternoon that a storm or
two could become strong to severe given around 30 knots of deep
layer shear and around 1000 J/kg SBCAPE. However, given the marginal
thermodynamics this is unlikely. If a storm can become strong to
severe, winds up to 60 mph and small hail are the main concerns.

Additional storms are possible Thursday afternoon as the weak front
drifts southward. However with only weak frontal convergence and mid-
level height rises, it will be difficult for storms to develop and
they would be isolated if they did. Cannot completely rule out a
gusty storm, but the threat looks quite limited with HREF mean
SBCAPE even lower than today. SPC has removed the marginal risk for
West Michigan in line with this thinking.

Mid-level height rises and the associated capping continue into
Friday as a warm front crosses the region. While a low chance for a
shower or storm exists Friday, the chance is low enough given the
capping to keep precipitation out of the forecast with this package.

- Showers and Storms Possible Saturday Night into Sunday

Better chances of showers and storms exist Saturday Night into
Sunday as a mid-level wave drives a cold front across the area.
Notable uncertainty as to frontal timing remains with the GFS
roughly 12 hours faster than the ECMWF. This would have implications
on both available instability/thunder risk and high temperatures for
Sunday. The good news is that it will not be an all day washout for
the end of the Independence Day weekend even with rain in the
forecast.

- Warming Late Week Then Slight Cooling Next Week

The passage of the warm front Friday is marked by 850mb temps
climbing to near 20C with highs climbing into the upper 80s to mid
90s through Saturday. Dewpoints will be just high enough to put heat
indices in the upper 90s Saturday. 850mb temps fall towards 13-15C
behind the cold front Sunday putting highs early next week solidly
in the 80s.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 714 PM EDT Wed Jul 2 2025

Radar shows a broken line of shower/storms moving southeast over
Lake MI. The convection is weakening but may clip MKG around 01z
and we included a thunder mention in the MKG TAF. As the
precipitation continues southeast, it should continue to weaken
and only be showers if it gets as far as GRR. Elsewhere, the rest
of the terminals should remain VFR overnight. However, some cu
from the convection upstream may filter across the terminals.


&&

.MARINE...
Issued at 135 PM EDT Wed Jul 2 2025

Waves will remain aob 2 feet through Friday before southwest winds
increase Saturday. Waves will increase to 2-4/3-5 ft north of
Whitehall Saturday afternoon and a small craft advisory may be
needed then.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.

&&

$$

DISCUSSION...Thomas
AVIATION...04
MARINE...04