059
FXUS63 KGRR 081136
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
736 AM EDT Tue Jul 8 2025

.KEY MESSAGES...

- Smaller shower/storm chances today through Wednesday

- Mainly dry Thursday and Friday

- Better shot of widespread rain Saturday

&&

.DISCUSSION...
Issued at 341 AM EDT Tue Jul 8 2025

- Smaller shower/storm chances today through Wednesday

We are starting out the forecast period with mainly some mid and
high clouds floating overhead this morning. We are watching a few
showers over Eastern Wisconsin that formed earlier on the leading
edge of better instability and a weak 15-20 knot low level jet
core traversing east. It is not out of the possibilities that one
of these showers could survive, and affect the lakeshore counties
later this morning. This will be a 10-20% chance, meaning most of
the area will stay dry.

The better chance for a few showers and maybe a storm will come
later today through the first part of Wednesday. We will see the
instability gradient at the sfc and aloft push over the area this
afternoon. The chance for any one site to see rain is not very
high, staying in the chance category. This is because overall
moisture is limited with having lost the humidity in the last 24
hours, and not seeing any significant advection of better moisture
back in.

The best chance of this whole period will be across the eastern
portion of the forecast area on Wednesday afternoon. This will be
when we see forcing via the upper short wave, sfc front, and some
moisture return by then with diurnal instability.

- Mainly dry Thursday and Friday

Upper ridging will build over the area on Thursday in the wake of
the upper short wave and sfc front that moves through on
Wednesday. Sfc ridging will pass right overhead on Thursday,
before moving east by Friday. There is a weak short wave that
moves in Friday, but the models are showing dry conditions
persisting with a lack of moisture return by then.

- Better shot of widespread rain Saturday

One of the better chances for a more widespread rain event over
the last few weeks is looking likely to affect the area centered
on Saturday.

We will have one wave currently offshore of Northern California that
will approach the area early Saturday. As this wave moves in, a
stronger wave will be diving in from the NW. The CA wave is
looking to be enhanced by the wave coming in from the NW due to
the divergence occurring ahead of the second wave. The moisture
flow ahead of it is not ideal, but the synoptic forcing and low
level jet transporting moisture ahead of it, combined with a
diurnal boost will all bring higher chances of a rain Saturday.

If some sunshine can occur ahead of the showers and storms with
the front, instability will increase, and decent mid level winds
in place will help support storm organization. Still a ways out
yet to get into any more details at this point.

We will see a break in the weather on Sunday, before another weak
short wave and associated sfc front move in to bring another
chance of rain on Monday.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 736 AM EDT Tue Jul 8 2025

The majority of the day for the terminals will see cumulus
development with clouds around 6k ft agl, and mid cloud cover
rolling in from showers and a few storms over Wisconsin earlier.
The current thinking is KMKG will be the main terminal to see
maybe a few light showers. The rest of the sites are likely to
miss out on the showers early this morning.

Additional showers and isolated storms are expected to fire this
evening into the overnight hours. These look to be possible after
about 02-03z, and will continue into the night. We have no
restrictions to ceilings or visibility for now. We will continue
to fine tune the forecast through subsequent issuences.

&&

.MARINE...
Issued at 341 AM EDT Tue Jul 8 2025

We will see a break today in the higher winds/waves that have
been present the last few days, before another possible event
develops on Wednesday.

We will see flow from the SW become established today out ahead of
the next incoming front for later tonight and early Wednesday.
These winds should stay rather tame, generally under 20 knots.

Wednesday, we will see the relatively weak cold front move
through. We are looking at another of the type of event we saw
Monday with a tight mesoscale pressure gradient setting up right
along the lakeshore with the departing front and incoming ridge.
Another set of marine/swim headlines are possible, but will hold
off for now.

&&

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

&&

$$

DISCUSSION...NJJ
AVIATION...NJJ
MARINE...NJJ