Portage, Michigan 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

318
FXUS63 KGRR 150549
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
149 AM EDT Wed Oct 15 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 /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 149 AM EDT Wed Oct 15 2025

Light rain is moving through Southwest Lower Michigan at 06z. The
rain is quite light and VFR weather is occurring at all
observation sites. The rain is falling from a mid deck of clouds
in the 6,000-10,000 foot range. We do not envision visibilities
being affected or lowered by the rain. We also feel ceilings will
remain at or above 6,000 feet. The rain will end around 12z across
the area and ceilings will slowly begin to rise. By mid afternoon
we expect clearing to take place. VFR weather is forecast
throughout the entirety of this TAF period...06z to 06z. Winds
will generally be from the north to northeast at 10 knots or less.

&&

.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...None.

&&

$$

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