11-12-25 @ 1 PM – Taking a look at the latest data from the 12z runs, the trend continues: the deep Pacific low is dropping south off the coast before swinging inland. That track is creating a real challenge in the short-term forecast.

Instead of moving straight in like last month’s system, this one is dropping into California from the northwest with a broad warm sector and a marine air mass. There’s plenty of moisture in play, but the air mass isn’t cold, and that’s keeping snow levels higher than what we were seeing yesterday.

Since this is a Pacific system and not a cold-core storm, we’re not dealing with a deep pool of Arctic air. The lower snow levels in earlier forecasts were tied to the idea of a cold pool dropping in, but the latest runs make it clear that’s not happening.

That means snow levels will be higher, and at Mammoth, we’ll see a good mix of rain and wet snow at Main Lodge on Thursday. Accumulations down low will be questionable until later Thursday night, when the column cools and we start to see better flake production.

Up Top, though, things look better. The Summit should do well with this storm thanks to a steady feed of Pacific moisture and a decent southwest flow that will line up in the Mammoth slot for part of Thursday.

The ECMWF and GFS both show between 1.2 and 1.8 inches of liquid up high through Friday night, which looks about right. The NBM is still overdoing it, but we’ve learned to take that with a grain of salt in these warmer setups. The ECMWF ensembles are backing off a bit, which aligns with the QPF trend over the last 24 hours. 

Snowfall ratios will be low during the first half of the storm. During the day on Thursday, snow ratios will run around 4:1 near Main Lodge, 5:1 at McCoy, and 6:1 at the Summit. Thursday night, things cool down, and ratios come up to around 7:1 across the mountain, maybe 8:1 at the very Top if a heavier band sets up.

On Friday, the backside of the system brings lighter showers with similar ratios, around 6:1 to 7:1. It’s dense stuff, not powder by any means, but perfect for building a lasting base on the upper mountain.

Using those ratios with the latest model blend, here’s what looks reasonable for snowfall totals through Friday night. Up Top around the Summit, we’re looking at 10 to 16 inches of heavy, wind-packed snow. McCoy should come in around 6 to 10 inches, most of that falling Thursday night into early Friday when the column cools down a bit.

At Main Lodge, expect 2 to 5 inches of wet snow, with periods of rain, and the best chance for it to stick late Thursday night. Town should see mostly rain, with a dusting possible early Friday if the colder air digs in before the precipitation shuts off.

The Mammoth slot adjustment applies here, but only during the southwest flow phase on Thursday afternoon into early evening. That’s when the mountain is aligned perfectly for enhancement. Once the low pivots and the flow goes more southerly, that effect drops out, so the bump in totals is minimal this time.

Winds will be strong at the ridge Top, with southwest gusts likely to cause blowing and drifting snow Thursday night. For the ski area, this is ideal base-building snow. The rain at the start will help freeze the ground, and by the weekend, we should have a frozen layer to work with as colder air settles in.

Down in town, look for mostly rain through Thursday with snow levels dropping near 8,000 feet by early Friday morning. Some slushy conditions are possible on the road early Friday if temperatures drop a bit quicker than expected, but the bigger travel impacts should stay above Main Lodge.

Looking beyond this system, the long-range ECMWF ensembles hold a broad trough over the West into next week, keeping things unsettled. That should allow a few weaker waves to move through, maintaining snowmaking temps and the potential for additional light snow accumulations on the mountain.

Ski Ya Later, Snowman Out… The next discussion update will be by 2 PM on Thursday.