557
FXUS63 KGRR 081122
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
622 AM EST Mon Dec 8 2025

.KEY MESSAGES...

- Light snow focused on NW tonight, with possible freezing drizzle

- Accumulating snow north, mix south Tuesday night/Wednesday

- Active La Nina winter pattern continues next weekend

&&

.DISCUSSION...
Issued at 327 AM EST Mon Dec 8 2025

- Light snow focused on NW tonight, with possible freezing drizzle

We are issuing a Winter Weather Advisory for Mason County for
tonight and Tuesday for snow and a possible wintry mix.

We are seeing a break this morning in the unsettled and wintry
pattern that has taken over the area over the last couple of weeks.
It is a quite cold morning with clear skies and light winds under
the sfc ridge, along with a fresh snowpack across the area.

This break will be short lived through later this afternoon, before
the next system begins impacting the area. The beginning of the
event will be a small mesoscale feature forming over the lake today
with the land breezes taking control. A narrow convergence band is
expected to develop and float NNE up the lake to affect mainly Mason
county and northward beginning late this afternoon.

Shortly after that begins, we will see the main precipitation shield
associated with the next clipper system gradually spread across much
of the area. This is similar to the systems late last week where the
systems are generally moisture starved, and a general trace to 2
inches of snow falls. Then, sufficient lake instability and moisture
from Lake Michigan enhances it where the flow is directly off of the
lake, mainly the NW corner of the forecast area. Mason will see the
mesoscale band and best snow amounts, and therefore was placed in an
advisory. The surrounding counties to the East and South will be
marginal for advisory amounts/conditions, so will hold off for them
for now.

Another potential problem that has revealed itself as the details
become more clear with this system is that there is a potential of
some drizzle/freezing drizzle as the precipitation comes to an end
on Tuesday. Forecast soundings and RH/temp cross sections show that
we may end up with an unsaturated dgz for a short period of time
Tuesday morning. Areas right near the lake may end up just above
freezing, while most inland sites will likely stay just below
freezing. We will monitor this potential for a possible need of
additional headlines if confidence increases, and it looks to be
long enough to cause impacts.

- Accumulating snow north, mix south Tuesday night/Wednesday

We have been anticipating a busy period from tonight through
Wednesday with little relief, and that remains the case. We will see
precipitation (snow, fzdz, etc...) come to an end by early Tuesday
afternoon, only to see precipitation move back in now maybe as early
as the end of the rush hour over the NW counties Tuesday evening.

This system has been shown for a while now to be the more potent
one, and could be quite messy with precipitation types. The upper
jet streak feeding the system is almost 160 knots, and we have the
LFQ of that jet, and some RRQ coupling of the departing system
enhancing the large scale lift.

The jet nearby implies that the strong temperature gradient is
nearby, which is the case, unlike the past clipper systems we have
seen. The lack of good deep moisture is being compensated for by
quite a bit of strong forcing moving right over the heart of the
forecast area.

We will see light to moderate snow develop Tuesday evening across
the entire area. Then, we will see warm enough air move in roughly
along and south of I-96 to change the snow over to rain. This is
based on a increasingly good ensemble consensus that the sfc low
will track near or just north of I-96. This system does not look
conducive over our area to produce some if any freezing rain or
sleet. Forecast soundings show that the warming takes place mainly
in the lower couple of thousand feet, and not much potential for an
elevated melting layer to produce the melting and re-freezing needed
for those types.

The locations that end up seeing snow change to rain will obviously
see less snow accumulate. Areas near and north of the low track will
see all snow, and will likely be multiple inches being in the
favorable pivot point between the pcpn ahead of the system, and the
deformation zone with the upper wave trailing behind. Right now,
snow amounts look like a solid advisory event, and could approach
possible warning amounts. Confidence is not high enough at this time
to pull the trigger on a watch, but we will continue to monitor the
trend.

We will see the mixture of rain and snow change to snow showers
Wednesday afternoon and evening as the colder air moves in, and some
lake effect develops with upper cold pool and cyclonic flow moving
overhead. An additional short wave then drops down Wednesday night
from the NNW, and will likely enhance the snow showers at that time.

- Active La Nina winter pattern continues next weekend

Additional snow shower chances remain in the latter portion of the
forecast period out toward next weekend. This is the case as the
pattern remains similar where the broad upper ridge over the eastern
Pacific/Western U.S. coast transitions to broad troughing here, and
a upper flow from the WNW continues the Clipper wave train. This is
the classic La Nina pattern. Timing this far out is obviously
problematic, but we look to have a couple of waves move through from
Friday through Sunday. This spells more cold and snow for the
foreseeable future.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 622 AM EST Mon Dec 8 2025

Much of this forecast period will be quiet with VFR conditions. We
are starting out with just a thin high deck of clouds this
morning. There has been some patchy fog at KAZO and KBTL, but it
seems to have disappeared in the last hour or two. We will see
some additional mid level clouds move in during the daylight
hours. Maybe some lake effect clouds at KMKG at times later as the
flow becomes more onshore. Not enough of a change with a light
wind regime to necessitate a change group.

After 00z we will see some potential of some light snow at KMKG,
along with lower conditions at least into MVFR to IFR. The better
chance will be after 06z. Some of this might come into KGRR,
KAZO, and KBTL before 12z Tuesday, but the chances are lower as
most of it will stay north. We have brought in some MVFR clouds.
We will also see low level wind shear develop after 06z as a 45-50
knot core of wind moves over the area around 2-3k ft agl. With
winds at the sfc much lighter and backed in direction a bit, felt
it was strong enough to mention.

Right at the end of this forecast period and more likely just
after, a chance of some freezing drizzle will develop as we lose
the deeper clouds.

&&

.MARINE...
Issued at 327 AM EST Mon Dec 8 2025

We are issuing a Gale Warning for the northern marine zone for much
of tonight, and a Small Craft Advisory tonight into Tuesday night
for the remainder of the area.

The gradient will be tightening up over the marine areas beginning
today, and continuing through the first half of the week. This
occurs as we see a couple of stronger systems affect the area
through Wednesday. The strongest of the winds through tonight will
be over the northern half of the lake. Gales are likely north of
Pentwater. There may some brief Gale gusts further south, but they
do no look to be persistent long enough to justify a Gale. So a SCA
was issued for elsewhere.

There will be a brief break in the winds centered around Tuesday
afternoon, but waves will not come down enough in that brief break,
before the winds increase again Tuesday evening. So we have the SCA
going through 06z Wed. It is at this time that a Gale may eventually
be needed depending on the trends.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory from 7 PM this evening to 4 PM EST
     Tuesday for MIZ037.
MARINE...Small Craft Advisory from 7 PM this evening to 1 AM EST
     Wednesday for LMZ844>846.
     Small Craft Advisory from 4 PM this afternoon to 1 AM EST
     Wednesday for LMZ847-848.
     Gale Warning from 11 PM this evening to 7 AM EST Tuesday for
     LMZ849.

&&

$$

DISCUSSION...NJJ
AVIATION...NJJ
MARINE...NJJ