GNFAC Avalanche Forecast for Sat Dec 21, 2019

Not the Current Forecast

Good Morning. This is Ian Hoyer with the Gallatin National Forest Avalanche Forecast on Saturday, December 21st at 7:00 a.m. Today’s forecast is sponsored by Grizzly Outfitters and Spark R&D. This forecast does not apply to operating ski areas.

Mountain Weather

Two inches of snow fell overnight near Cooke City. The rest of southwest Montana stayed dry. This morning temperatures are in the 20s to low 30s F with strong south and west winds. Breezy conditions will continue through the day with mostly clear skies and mountain temperatures rising into the 30s and potentially low 40s F.

Snowpack and Avalanche Discussion

From Big Sky to West Yellowstone there is widespread weak snow at the ground. This weak snow will be will us for weeks, if not months, to come. With each additional day without a load of new snow, this weak foundation is slowly adjusting and you’re becoming less likely to trigger a slide (video). However, triggering an avalanche remains possible if you find just the wrong spot. Signs of instability have become less frequent. Without these clues to guide you, the first sign of trouble may be triggering a slide. Remain wary of any slope with a cohesive slab above the weak snow at the ground. Wind drifted areas are more likely to have this combination. Avoid these slopes or dig to see if the weak layers are still reactive. Today, the avalanche danger is rated MODERATE.

Triggering an avalanches remains possible today on slopes with crusts and weak layers in the middle of the snowpack. Alex was in Cooke City for the last couple days and was finding this facet-crust combination still reactive on sunny slopes (video). He also found thin wind slabs forming yesterday. Without much new snow to move around these slabs shouldn’t be much of a problem on their own, but they are adding just enough weight to keep the weak layers mid-pack awake.

Dig down to look for these weak layers. The snowpack is still relatively thin, so it won’t take too long. Avalanches are possible and the avalanche danger is MODERATE today.

It’s been five days since the last snowfall and the snowpack is generally stable. However, there are still a couple isolated avalanche concerns. Watch out for heavily wind drifted pockets, particularly if you’re getting into steeper terrain where a small slide could have big consequences. With the unseasonably warm temperatures and blue skies today, you could also trigger a small loose snow slide near rocks on the sunniest slopes. Enjoy the temperate conditions, but keep avalanches in the back of your mind. For today, the avalanche danger is rated 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.


January 15 & 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.


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.

The Last Word

The Utah Avalanche Center has posted the full accident report from last Sunday’s avalanche fatality near Park City. The report is available HERE.