002
FXUS63 KGRR 092353
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
753 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 /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 753 PM EDT Thu Oct 9 2025

Surface high pressure is sliding away to the east tonight, but it
will provide another night of light winds and clear skies. VFR
weather will continue well into Friday. The focus now shifts to
the northwest and an approaching cold front. The front as we
approach 00z stretches across the Dakotas from a low entering
northwest Minnesota. The front will push our direction through the
night and bring lowering and thickening ceilings Friday afternoon.
At this point, we believe we will remain VFR into the afternoon on
Friday. Rain will spread into West Central Lower Michigan in the
afternoon. Ceilings will likely dip into the MVFR category right
around 00z and for a few hours beyond. Winds will increase out of
the south-southwest during the day on Friday, reaching 10-20 knots
at most sites after 14z. MKG will see the strongest winds with
gusts into the 20-30 knot range.

&&

.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