GNFAC Avalanche Forecast for Sat Dec 28, 2019

Not the Current Forecast

Good Morning. This is Ian Hoyer with the Gallatin National Forest Avalanche Forecast on Saturday, December 28th at 7:00 a.m. Today’s forecast is sponsored by Spark R&D and Gallatin County Search and Rescue. This forecast does not apply to operating ski areas.

Mountain Weather

This morning temperatures are in the single digits to low teens F and there is no new snow. Winds are 5-10 mph out of the north and west and will remain steady throughout the day. High temps will be in the teens F. Snow flurries today and tonight won’t bring significant accumulations.

Snowpack and Avalanche Discussion

Triggering large avalanches is possible in the mountains near Big Sky and West Yellowstone. The widespread weak snow near the ground is still working to accommodate the load of new snow that fell earlier this week (video). Have you noticed that we sound like a broken record? Every day: “weak snow at the ground … don’t trust it”. Well, get used to it. These weak layers don’t heal quickly. That’s why they are called persistent weak layers. We’ll be worried about these layers for weeks, if not months, to come. Each day without a new load avalanches become less likely, but this is a slow process and can’t be rushed. Avoiding riding on or beneath steep slopes is a simple way to stay safe while we wait. If you do get onto a steeper slope today, ride one at a time and have your partners watch from a safe spot, so they’re ready if something goes wrong. Human triggered avalanches are possible and the avalanche danger is MODERATE.

Yesterday, a rider saw two fresh large avalanches on a NE aspect of Henderson Mountain with snowmobile tracks nearby (details and photos). It’s unclear if these broke naturally or were triggered by the snowmobilers. Either way, these slides are a cause for concern. They broke several hundred feet wide and up to four feet deep. That is a lot of snow moving downhill and not something you want to mess around with. Triggering a similar slide is possible today on weak layers buried in the middle of the snowpack. Think carefully about the consequences of triggering an avalanche and make a solid plan before getting into steep terrain. The avalanche danger is MODERATE.

The lower snowpack is generally stable. Thin wind slabs formed by moderate west winds yesterday are the primary concern but won’t be much of an issue outside of the steepest high consequence terrain. Look out for these wind drifts near the ridgeline and avoid them if you’re in a place where a small slide would be a big deal. Today, large avalanches are unlikely and the avalanche danger is LOW.

If you get out, please send us your observations no matter how brief. You can fill out an observation form, email us (, leave a VM at 406-587-6984, or Instagram (#gnfacobs).

Upcoming Avalanche Education and Events

Our education calendar is full of awareness lectures and field courses. Check it out and plan to attend one or two: Events and Education Calendar.


Every Friday and Saturday, Snowpack Update and Rescue Training. Friday, 6:30-7:30 p.m. at the Soda Butte Lodge. Saturday anytime between 10-2 @ Round Lake.


January 4, 1-hr Avalanche Awareness, 7-8 p.m. at West Yellowstone Holiday Inn.

January 25, 1-hr Avalanche Awareness, 7-8 p.m. at West Yellowstone Holiday Inn.


January 7, Women's Specific Avalanche Awareness + Beacons, 6-8 p.m. at Story Mill.

January 8, 1-hr Avalanche Awareness, 6-7 p.m. at REI.

January 10 & 11, Companion Rescue Clinic, 6-8 p.m. on the 10th at REI and 10-2 p.m. on the 11th at History Rock. More info and Register Here.

January 15 and 16, Introduction to Avalanche w/ Field Course, evenings of January 15 & 16 plus one field day either January 18, 19 or 25. Snowmobile specific field day offered January 25. More info and Register Here.

The Last Word

The Lionhead Weather Station is finally up and running! You can access the data here.

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