textproduct: Grand Rapids

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.