666
FXUS63 KGRR 151752
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
152 PM 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 /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 152 PM EDT Tue Jul 15 2025

VFR prevailing through late this evening. Lingering haze/smoke
this afternoon but greater than 6 mile visibility, and a few
cumulus clouds with bases around 4,000 feet. Scattered to broken
clouds at 5,000 to 6,000 arrive late tonight, and scattered rain
showers could develop during the early morning hours of Wednesday.
Ceilings may descend to MVFR by mid day Wednesday, and scattered
thunderstorms could develop.

&&

.MARINE...
Issued at 152 PM EDT Tue Jul 15 2025

Low swim risk and 1 to 2 ft waves through Wednesday with a wind
component mostly from the south. Thunderstorms will attempt to
cross Lake Michigan late Wednesday evening and some may be
successful. If so, lightning and wind gusts greater than 30 or 35
knots would be possible. Small craft advisory and beach hazards
statement (high swim risk) is likely for Thursday as winds
strengthen from the north.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Air Quality Alert from midnight tonight to midnight EDT
     Wednesday night for MIZ050-056-057-064-071.
MARINE...None.

&&

$$

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