757
FXUS63 KGRR 242254
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
654 PM EDT Sun Aug 24 2025

.KEY MESSAGES...

- Scattered showers and remaining cool through Tuesday

- Moderating temperatures mid week with next rain chance Thursday

- Cooling down next weekend with mainly dry conditions expected

&&

.DISCUSSION...
Issued at 300 PM EDT Sun Aug 24 2025

- Scattered showers and remaining cool through Tuesday

No real adjustments are needed at this time to the general forecast.
Colder air aloft coming in is evident on both the IR imagery with
cloud tops much cooler, and the WV imagery with the upper trough
moving in. In addition, the next line of showers dropping down Lake
Michigan offshore of Manistee county at 230 PM now contain lightning
as has been advertised the past couple of days.

The coldest air aloft will continue to move in this afternoon with
500 mb temps dropping from -14C this morning to -18 to -20C later
today into Tuesday. This drop in the mid-upper levels is allowing
the inversion heights to increase significantly to almost 30k ft agl
with lake modified parcels considering the water is 70+ F
degrees/low 20s C.

We will be holding the highest pops for the first two rows of
counties along the lakeshore into Tuesday, in addition to the main
lightning threat. Can`t rule out some lightning up north today as
some slightly unstable conditions without the lake are present up
there today. Then, the same thing happens along the southern
counties on Monday. We will see the upper levels of the atmosphere
warm a bit on Tuesday as the upper trough gradually pulls away that
day.

- Moderating temperatures mid week with next rain chance Thursday

Short wave ridging will build over the area on Wednesday in the wake
of the upper low moving east. This building subsidence and much
lower inversion heights will really limit the vertical development
of any updrafts that try to go up.

The break in the rain chances will be short however as the NW flow
aloft continues to hold over the area. This will help to steer
another formidable short wave toward the area. The latest consensus
timing on this short wave is that is will be pushing through at peak
heating on Thursday. We are not however looking at much rain from
this stronger system, as there is not a lot of moisture associated
with it with the source region ahead of the front coming from the
Central Plains, and not the Gulf. The system will have to rely on
diurnal instability to muster much more than a few scattered showers.

- Cooling down next weekend with mainly dry conditions expected

The trough will move through Thursday night, with a secondary trough
coming through Friday morning. One can not rule out a chance of a
rain shower until Friday afternoon as a result. However, the limited
moisture ahead of the first sfc front and upper wave will be swept
out. This will leave even less moisture to be available, not to
mention a passage during min heating.

We will see short wave ridging then build in aloft by Saturday. This
will support another Canadian sfc ridge that will reinforce the
cooler air over the area, but with an offshore flow. This should
limit lake effect chances to maybe our far eastern counties coming
in from Lake Huron. It looks to be mostly dry at this time.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 654 PM EDT Sun Aug 24 2025

Ongoing lake effect showers with isolated thunderstorms will
diminish somewhat overnight as the assist from diurnal heating is
lost. As flow veers northwesterly the best chance for any showers
will be at MKG and AZO followed by BTL. Brief periods of MVFR
conditions are possible in any showers. Otherwise expect the lake
induced stratocu to persist with VFR ceilings through the night
and into Monday. Monday morning, the arrival of a mid-level
disturbance will allow showers to move inland however confidence
in terminal impacts is low (20-30 percent) so have kept LAN/JXN
dry with this issuance. Gusts to 20 knots will diminish after
sunset before increasing again late Monday morning into the
afternoon.

&&

.MARINE...
Issued at 300 PM EDT Sun Aug 24 2025

Ongoing Small Craft Advisory/Beach Hazards Statement are in good
shape this afternoon with webcams and buoys showing 3 to 5 foot
waves are occuring on Lake Michigan. Increasing northwest winds will
drive gusts to 25 knots for the afternoon and evening, and 3-5 foot
waves will continue across the nearshore waters through Monday
evening creating hazardous conditions for boaters and swimmers.

In addition, the cold airmass makes for a favorable setup for
waterspouts and thunderstorms through the evening and into tonight.
The risk for waterspouts will subside later Monday as instability
over the lake lessens. Mariners should be alert for and stay away
from any waterspouts as winds in excess of 34 knots are possible in
any waterspouts that develop.

Tuesday and beyond will feature more subdued conditions on the lake
as the gradient weakens and the cooler airmass begins to shift east.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement through Monday evening for MIZ037-043-
     050-056-064-071.
MARINE...Small Craft Advisory until 8 PM EDT Monday for LMZ844>849.

&&

$$

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