399
FXUS63 KGRR 161146
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
746 AM EDT Thu Oct 16 2025

.KEY MESSAGES...

- Potential for some light precipitation tonight into Friday

- A wet and windy weekend

- Another system set for Tuesday/Wednesday

&&

.DISCUSSION...
Issued at 408 AM EDT Thu Oct 16 2025

- Potential for some light precipitation tonight into Friday

Today will bring rather calm and quiet weather to the region as
high pressure is in place both at the surface and aloft. The
initial push of warm air advection in advance of our next system
comes tonight into Friday morning. The best moisture transport
occurs across Northern Lower Michigan. The SREF pops almost always
seem superior to other guidance and will follow its lead here. We
will carry small pops across Central Lower Michigan to account
for showers that will be moving across the area tonight into
tomorrow morning.

- A wet and windy weekend

A cold front will be located just west of the area in the Friday
night and Saturday time frame associated with the initial wave
moving into Canada today from the Plains. A little bit less in the
way of precipitation is expected initially now, with a period of
dry weather expected as we away for energy to drop into the base
of the upper trough as we head into Saturday night. A deep low is
expected to from in the Great Lakes this weekend, but the energy
that drives and deepens that low is currently all the way up in
the Gulf of Alaska west of British Columbia Canada. It has a long
way to traverse before it induces a strong deepening low into
Sunday over the Great Lakes. So, while the nearby cold front will
have some rain associated with it on Saturday, the bulk of the
activity gets going with the upper wave begins to round the base
of the upper trough to our west Saturday evening. Using the GFS,
the surface low deepens from 998mb in Iowa Saturday evening to
989mb just north of Lake Huron Sunday evening. This is a strong
low for sure, but nothing that out of the ordinary by the
standards of fall Great Lakes systems. The backside high is not
abnormally strong either, around 1020mb. The expectations are for
a windy system this weekend with sustained winds likely in the
20-30 mph range with gusts of 40-50 mph. WE are likely looking at
the potential of a Wind Advisory on Sunday at least for portions
of the area. Given the dynamics in play with a strong upper jet
over 100 knots and the moisture return of 60+ F surface dewpoints,
thunderstorms are expected in the warm sector Saturday night into
Sunday morning. WPC QPF totals are in the 1-2 inch range over the
next 5 days with most of that coming this weekend. We should be
able to handle that rain without issues given lower river levels.

- Another system set for Tuesday/Wednesday

Another system is expected into mid next week in the Tuesday and
Wednesday time frame. The deep upper trough of this weekend is
followed by an even deeper upper system as we head into next
Wednesday. The upper trough has a reinforcing shot of cold air
with 850mb temperatures dipping to below zero C. Widespread rain
showers are expected along with blustery conditions. Fall has
arrived!

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 746 AM EDT Thu Oct 16 2025

Some light morning fog will continue off an on for another hour or
so (through 14z) at AZO and JXN. The fog is of the shallow
radiation variety and should mix out quickly with sunrise
occurring soon, just before 800am. High pressure will bring mainly
clear skies today along with very light winds out of the east.

Tonight a mid deck of clouds will spread in and lower to around
9,000 feet. We will see some showers develop across Central Lower
Michigan late tonight, but we feel this activity will stay north
of the TAF sites. Cannot rule out an isolated shower at the I-96
TAF sites after 06z, but the threat is too low to include at this
point.

&&

.MARINE...
Issued at 408 AM EDT Thu Oct 16 2025

Lake Michigan is quiet this morning with offshore winds around 10
knots and 1 foot waves. Winds will become even lighter today so
no marine concerns through sunset. Tonight winds begin to pick up
out of the south at about 10 knots as surface high pressure slips
away to the east of the Great Lakes.

On Friday winds will likely increase to Small Craft Advisory (SCA)
strength as the gradient tightens between the retreating high and
low pressure in the Northern Plains. 15 to 30 knot south winds
look like a reasonable bet from around daybreak on Friday into the
day on Saturday. A SCA will be needed for Friday into Saturday
for these stronger south winds.

The focus is on a the potential for strong winds over Lake
Michigan this weekend. The evolution of the low is the question
mark at this point. How and where the low deepens and to what
strength is the crux of the Saturday night through Sunday night
forecast. The energy that will be responsible for this weekends
potentially strong low is in the Gulf of Alaska this morning
between British Columbia Canada and the state of Alaska. So, it
has a long way to traverse and models are handling its evolution
differently. At this point look at both operational and ensemble
guidance the event has the potential to produce high in gales (to
45 knots) with some storm force gusts not out of the question
(near 50 knots). This event is 4 days out so we have time to dial
in the forecast based on new guidance. Bottom line, expecting a
high end gale on Sunday with waves that will likely peak in the
12-15 foot range.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.

&&

$$

DISCUSSION...Duke
AVIATION...Duke
MARINE...Duke/Thomas