343
FXUS63 KGRR 151131
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
731 AM EDT Tue Jul 15 2025

.KEY MESSAGES...

- Shower/storm chances Wednesday through Thursday

- Cool down and drier air coming Thursday and Friday

- Shower and storm chances return Saturday

&&

.DISCUSSION...
Issued at 335 AM EDT Tue Jul 15 2025

- Shower/storm chances Wednesday through Thursday

The area will see one more dry day today with temperatures moving up
a couple of notches as compared to Monday. High pressure is shifting
SE this morning, and low level winds from the SSE to SSW will work
together with increasing heights to provide some 90 degree readings
this afternoon. Dew points will inch up a little compared to Monday,
but will not be oppressive yet as they reach into the low to mid
60s.

The heights building a bit will set the area up to see a weak short
wave approach the area from the SSW later tonight and Wednesday.
This wave along with some additional moisture will bring a small
chance of a few showers across our far south portion of the area as
soon as early Wednesday morning.

The wave will slip southeast of the area by daybreak Wednesday
morning. Even though this wave will be out of play for the area,
rain chances will persist on Wednesday and into Thursday. The
additional moisture that will have advected in will yield MU CAPES
of 2,000+ J/kg by late Wednesday morning with dew points well into
the 70s. We will not have any major synoptic features to kick them
off, but the lake breeze will help to focus development, along with
convective temperatures being easily reachable. The good news is
that severe weather is not likely Wednesday afternoon with deep
layer shear values only 20-25 knots.

That threat will diminish after sunset, but the rain chances will
not drop off much. This is because we will have a weakening short
wave that will approach after sunset. This wave will be responsible
for a bit more robust convection to our WSW in WI/IL/IA as it moves
through during peak heating. Deep layer shear is more favorable with
the wave, on the order of 35 knots or so. We will hold the
instability with the flow ahead of the wave, albeit may be more
elevated being after sunset.

We do expect it will lose its strength as it approaches. The wave
weakens a little, and will be focused just a tad north of the area.
The best instability looks to stay south of the area. We could see a
situation where the best rain chances will end up north and south of
the area, with a relative min for our area.

We will see a cold front drop down into the area on Thursday, and
another short wave will approach Central and Northern Lower Thu
morning. Between the possible showers/storms earlier in the night,
and morning timing of the front and wave, widespread additional
showers and storms do not look to be likely.

- Cool down and drier air coming Thursday and Friday

The clouds holding down heat Thursday morning, and cold front coming
through by early afternoon, we will see temperatures not nearly as
warm as Wednesday. Decent flow behind the front will usher in a much
more comfortable air mass across the area. Rain chances will end
early, and dry weather will accompany the cooler weather for Friday.

- Shower and storm chances return Saturday

The trend for Saturday is for higher chances of rain as compared to
the general data over the last 24 hours. We see short wave energy
ejecting out from an upper low over the Desert SW. The wave will
potentially bring the sfc front to our S, back north toward the
area. The low level flow will be directly advecting moisture from
the Gulf. This could be setting the area up for widespread
showers/storms Saturday evening if the front is just south of the
area.

This wave could suppress the front once again once it passes by to
our east. If this is the case, we would end up cooling off again,
and delaying a return to heat until after this forecast package.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 731 AM EDT Tue Jul 15 2025

Some fog did indeed form at KJXN, KBTL, and KAZO early this
morning, and even some BCFG at KGRR. The fog will not last much
longer with the sun now up and mixing the moist boundary layer
out. Some of the low level moisture may cause some lower cumulus
clouds to develop. These should stay few-sct with some high
clouds coming over the top of them.

The cumulus clouds will go away this evening, before some clouds
come in/develop around 5-6k ft as a weak system approaches the
area. There is even a chance of a shower that forms along the
I-94 terminals. They could happen as early as 03-05z, but are more
likely to happen after 08-10. We expect them to stay VFR at this
time.


&&

.MARINE...
Issued at 335 AM EDT Tue Jul 15 2025

Marine headlines will likely not be needed through Wednesday for the
area. High pressure that was over the area on Monday will slowly
move SE of the area. The pressure gradient remains rather weak, even
as a front approaches Wednesday.

Thursday is a different story as the front moves through, when Small
Craft Advisories and Beach Hazards Statements are likely to be
needed. There is a fairly tight gradient on the back side of the
system. In addition, there will be a push of noticeably cooler air
coming in over the warm lake. This will enhance the already decent
wind coming in and be efficient in building waves.

&&

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

&&

$$

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