647
FXUS63 KGRR 142201
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
601 PM EDT Tue Oct 14 2025

.KEY MESSAGES...

- Very Light Rain Tuesday Night

- Chance of Showers Friday Morning With a Brief Warmup

- Significant Pattern Change This Weekend

&&

.DISCUSSION...
Issued at 231 PM EDT Tue Oct 14 2025

- Very Light Rain Tuesday Night

Large scale ridging supports the ongoing dry conditions across the
area this afternoon. However, a ridge riding shortwave will cross
the region tonight providing sufficient forcing for a few rain
showers. However, there is a notable lack of moisture in the low-
levels with BUFKIT overviews showing moisture mainly concentrated in
the 700-400 mb layer. This will lead to a mix of virga and very
light showers, with HREF LPMM guidance suggesting a few hundredths
of an inch in accumulations. More notable rainfall is favored west
of the area where better moisture quality will be present.

- Chance of Showers Friday Morning With a Brief Warmup

Conditions dry out Wednesday morning as the mid-level wave clears
the area with surface and upper-level ridging dominating the
forecast later Wednesday into Thursday.

Our next chance of showers will be Friday morning as a warm front
crosses the Great Lakes. Moisture quality is not ideal supporting
PoPs in the 20-50 percent chance range, highest across Central Lower
Michigan where the better moisture resides. Behind this warm front,
850mb temps climb into the mid teens. This will bring highs into the
low and possibly the mid 70s by Saturday.

- Significant Pattern Change This Weekend

The primary focus over the next 7 days will be the more substantial
system that arrives for the weekend. The potent trough off the
coast of California will eject to the northeast and phase with a
northern stream wave. The resulting longwave trough replaces the
ridge and will feature several embedded shortwaves. Rain arrives
Friday Night into Saturday as a cold front accompanies one of
these waves, with forecast MUCAPE warranting a mention of thunder.
Showers will continue into Sunday as the trough persists
overhead.

However, uncertainty remains within the ensembles as to the specific
evolution of the trough including the potential for secondary
cyclogenesis over the Great Lakes region. This would affect winds as
well as rainfall potential. The GFS set of solutions is also notably
slower in clearing the trough than the ECMWF set, which would keep
rain showers into Monday as well. Regardless, much colder air
arrives with the trough and cold frontal passage. Highs will fall
into the 50s as 850mb temps fall to near 0C.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 601 PM EDT Tue Oct 14 2025

Incoming cloud layers tonight will become ceilings around 15,000
to 10,000 feet, lowering to 6,000 feet by morning. Areas of light
rain will be produced from these clouds late in the night, but
will be partially evaporating into drier air on the way to the
ground. Light rain may reach the ground once in a while, but
visibility is not expected to be much affected.

&&

.MARINE...
Issued at 601 PM EDT Tue Oct 14 2025

Recent trends include 20 to 25 knot northwest winds at Muskegon
GLERL, whitecaps offshore off the Grand Haven cams, Port Sheldon
buoy reporting 2 to 4 ft waves and increasing, and South Haven
buoy reporting 3 to 5 ft waves. Because of this and the broader
picture across Lake Michigan, a small craft advisory is in effect
for Tue evening until midnight.

Winds will become more from the northeast late tonight and keep
the larger waves over the open waters. Wed and Thu are expected to
have some 1 to 2 ft waves. Small Craft Advisory conditions are
likely starting early Friday and continuing through the weekend.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory until midnight EDT tonight for LMZ844>847.

&&

$$

DISCUSSION...Thomas
AVIATION...CAS
MARINE...CAS