textproduct: Grand Rapids

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.