985
FXUS63 KGRR 091930
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
330 PM EDT Thu Oct 9 2025

.KEY MESSAGES...

- Areas of Frost Possible Again Tonight

- Periods of Rain Friday through Saturday

&&

.DISCUSSION...
Issued at 330 PM EDT Thu Oct 9 2025

- Areas of Frost Possible Again Tonight

Another cooler-than-normal night ahead but more marginal
potential for frost. The surface high pressure center is migrating
to the Northeast US tonight, resulting in increasingly southerly
flow and warm advection in the lower atmosphere over Michigan.
There will be some patchy thin cirrus clouds also moving in.
However, neither factor appears to be enough to totally eliminate
the potential for areas of strong radiational cooling and spots of
decoupled wind at the surface tonight.

NBM Min Temp probabilities for less than 36 degrees favor the
climatologically cooler spots of the Central Michigan highlands
(Clare/Osceola) and the Irish Hills around Jackson County, with
the rest of Mid Michigan in between at lower chances but still
enough for some patchy frost. Also can`t rule out some patchy
frost in the typically cooler portions of counties that are just
west of the Frost Advisory.

- Periods of Rain Friday through Saturday

The chance of rain showers Friday afternoon is about 50 to 80
percent for west-central Lwr MI (mainly areas west of Grand Rapids
/ Mount Pleasant) per the HREF. The chances late Fri evening
spread southeast to encompass much of the area, but trend down to
about 40 to 60 percent, with the lower chances more toward
Jackson. Chances of about 20 to 40 percent linger into Saturday.
Rain totals will be rather meager except for west-central Michigan
where 0.1 to 0.3 inches is more favored with isolated higher-end
totals toward 0.5 inch possible.

The cause of this will be a compact upper-level low diving in
toward the Great Lakes from the northwest. This low will have
strong 500 mb vorticity and a closed low at the surface, but will
be vertically stacked and filling in (weakening) as it crosses the
Great Lakes. The rain chances and rain totals will also be
dependent on whether the low center tracks through Lower Michigan
or takes more of a Lake Huron to Toronto track.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 147 PM EDT Thu Oct 9 2025

High pressure sliding slowly away to the east of the Great Lakes
this afternoon and tonight will maintain a hold on our weather.
The high will provide light winds and mainly clear skies. Bottom
line, VFR weather is expected to continue this afternoon through
Friday morning. A cold front will approach the area from the
northwest Friday morning and by late in the TAF period, 15z to
18z, we will see VFR ceilings push into MKG. Not out of the realm
of possibilities to see an isolated light rain shower near MKG
16z-18z on Friday. Winds will be light out of the east and
southeast today at 5-10 knots. Winds will increase Friday after
14z out of the south at 10-20 knots.

&&

.MARINE...
Issued at 330 PM EDT Thu Oct 9 2025

Main focus of the marine forecast is associated with a low moving
through the Great Lakes region in the Friday and Saturday time
frame. We will be hoisting a Small Craft Advisory (SCA) from late
tonight through Saturday morning. Southerly winds increase
overnight and into Friday morning in advance of the low. Winds
turn northwest into Friday night behind the low. Waves will
correspondingly build to 3 to 5 feet north of Grand Haven by
daybreak on Friday. Waves will peak in the 6 to 9 foot range north
of Holland Friday afternoon. Friday night winds and waves will
slowly decline. Waves should finally fall below SCA criteria in
the mid morning to midday hours of Saturday.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Frost Advisory from midnight tonight to 9 AM EDT Friday for
     MIZ038>040-045-046-051-052-058-059-066-067-073-074.
MARINE...Small Craft Advisory from 5 AM Friday to 11 AM EDT Saturday for
     LMZ844>849.

&&

$$

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