232
FXUS63 KGRR 082026
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
326 PM EST Mon Dec 8 2025

.KEY MESSAGES...

- Two Rounds of Snow & Mixed Precipitation Through Wednesday

- Reinforcing Shot of Arctic Air and Snow Showers Fri-Sun


&&

.DISCUSSION...
Issued at 325 PM EST Mon Dec 8 2025

- Two Rounds of Snow & Mixed Precipitation Through Wednesday

We remain on track to receive a couple clipper systems through
Wednesday that will likely impact travel for portions of the region.
First up, the weaker of two short wave troughs arrives in the 06z-
12z Tuesday time frame. Low level moisture from the surface to 850mb
via SSW flow off Lake Michigan coincident with a saturated cloud
layer above the DGZ (seeder-feeder mechanism) will help provide a
modest combo of synoptic and lake effect snow production mainly
across Mason and Oceana Counties from 06z-12z/13z Tuesday. That
said, Nam3km and HRRR Bufkit overviews for LDM during this time
period show subsidence in the DGZ as opposed to lift. So while there
will be sufficient RH in that layer, we`ll lack appreciable omegas
based on the 12z guidance, so snowfall rates should not get out
of hand. Looking like 2"-4" with a few amounts nosing above 4"
across mainly Mason County, but Oceana is close enough to this
range that we`ve added them to the Winter Weather Advisory. The
timing was tweaked to start at 04z based on when impacts are
expected to begin occurring.

Outside of this area, a half inch to 2" or so is forecast. But once
again we look to have a setup where the DGZ becomes unsaturated
later Tuesday morning, likely after 12z. It is during this time that
precipitation should still be occurring but ice growth production
would be halted and surface temperatures will not yet have gotten
above 32F, leading to freezing drizzle or light freezing rain. A
consensus of short term, high-res model guidance for this event is
producing areas of light icing on the order of 0.01"-0.02"
especially across Muskegon, Ottawa, Kent, Allegan, and Barry
Counties (ie. HREF 24hr FRAM accretion). Unless amounts trend higher
with later guidance today/tonight, not thinking an Advisory is
needed, but will continue evaluating. Highs Tuesday look to top out
around 32F-33F inland but closer to 34F-35F by the lake.

The second and stronger of the two clippers arrives quick on the
heels of the first one, already moving into the Great Lakes by
Tuesday night. This system may throw a wrench into the Wednesday
morning commute especially from the I-96 corridor to the north due
to several inches of wet snow falling within the 00z-12z Wednesday
time frame as temperatures hover in the lower 30s. Snowfall rates
could reach 0.5" or more per hour in spots during the nighttime
hours, and when nocturnal cooling of road temperatures also occurs.

Warming temps in the 925mb-850mb layer from 06z-12z Wednesday
complicate the forecast a bit as a turnover to rain or a rain/snow
mix may occur near and south of I-96. If a switchover to rain does
occur, it may simply have the effect of creating a sloppy/slushy mix
on any roads that received some wet snow accumulation. Colder air
advects in on the back side of this system and precipitation should
turn back to all snow in the 12z-15z Wednesday time frame but with
light additional amounts, including some NW flow lake effect snow
showers into Wednesday afternoon/evening. At any rate, we`re likely
looking at an Advisory for a good chunk of the region for this
second system with an 80% or higher likelihood for at least 2" of
snow along and north of I-96 and storm total snowfall amounts likely
reaching 3"-6", highest amounts currently favored to be from M-46 to
US-10, with some adjustments/tweaks likely being made as the
guidance locks into the low track.

- Reinforcing Shot of Arctic Air and Snow Showers Fri-Sun

The coldest air of the season so far is showing up in some of the
ensemble guidance over the weekend as another reinforcing clipper
system may impact Michigan by Friday, bringing 850mb temperatures
behind it into the -15C to -20C range Saturday and Sunday. This
would yield high temperatures mainly in the teens to around 20F away
from the lake. Upper low formation around or just north of Lake
Superior is a possibility, with some vort maxes pivoting over the
region which would help with synoptic lift and lake enhanced
snowfall to areas along and west of US 131. This snow will likely be
quite powdery and finer grain. Almost all ECE ensemble members show
accumulating snow for the lakeshore region this weekend.

There are a few interesting takeaways from a global teleconnections
standpoint this month. The weak La Nina pattern continues, and the
Madden Julian Oscillation just moved out of a strong Phase 7 and
decent strength Phase 8, which correlate to colder than normal
temperatures across the northern U.S. Additionally, as we ended
November and moved into December, a sudden stratospheric warming
event occurred which is most easily tracked via a weakening and
reversal of winds at 10mb across 60N latitude. The winds did not
really reverse as they do during major SSW events, but still this
had the effect of weakening the polar vortex and shifting it off the
pole. While we haven`t gotten the full brunt of the polar vortex
here in Michigan, it likely has played some sort of role in
modifying the tropospheric weather pattern across our broader
region. All this to say is that one of the coldest starts to
December on record (top 10 for all climate sites through the first
week) is attributable to some of these factors.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 130 PM EST Mon Dec 8 2025

VFR conditions will continue through this evening. Snow moves
into west-central Lower Michigan after midnight with a quick
transition to IFR conditions at MKG and GRR and eventually the
rest of the area from LAN to AZO and JXN by 15Z Tuesday.

Snow transitions to freezing drizzle before ending around noon.
Some light icing is possible. LLWS to 45 knots is also possible
Tuesday morning. Surface winds will begin gusting over 20 knots
late tonight and continue through Tuesday afternoon, from the
south at first then turning southwest.

&&

.MARINE...
Issued at 325 PM EST Mon Dec 8 2025

SCA conditions begin this evening and last into tonight with
marginal gales possible north of Pentwater. This event may likely
pan out as a high end SCA north of Pentwater but kept the Gale
Warning going in that region overnight. Winds and waves subside a
bit into Tuesday afternoon but not enough to drop the SCA, and in
fact worsening conditions are much more likely Tuesday night into
Wednesday with both warm air advection (Tues PM) and cold air
advection (Wednesday) gales possible for our nearshore waters.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory from 11 PM this evening to 4 PM EST
     Tuesday for MIZ037-043.
MARINE...Small Craft Advisory from 7 PM this evening to 10 PM EST Tuesday
     for LMZ844>846.
     Gale Watch from Tuesday evening through Wednesday evening for
     LMZ844>849.
     Small Craft Advisory until 10 PM EST Tuesday for LMZ847-848.
     Gale Warning from 11 PM this evening to 7 AM EST Tuesday for
     LMZ849.
     Small Craft Advisory from 7 AM to 10 PM EST Tuesday for LMZ849.

&&

$$

DISCUSSION...Hoving
AVIATION...Ostuno
MARINE...Hoving