Good morning. This is Mark Staples with the Gallatin National Forest Avalanche Advisory issued on Friday, December 21 at 7:30 a.m. Today’s advisory is sponsored the Cliff Gullett Memorial Fund and the Pinhead Classic Telemark Festival. This advisory does not apply to operating ski areas.
Dry and windy weather continues. This morning temperatures were in the teens F and southerly winds were blowing 15-25 mph with gusts of 40-60 mph at the highest ridgetops. The exception is the Bridger Range which had temperatures in the low 20s F and calmer winds. Today will be partly sunny and temperatures will rise into the low 20s F while the Bridger Range could see temperatures approaching 30 F. Strong south winds will continue and only slightly ease by late afternoon. Light snowfall should come sometime Sunday with more possible for Christmas.
Bridger Range Madison Range Gallatin Range
Lionhead area near West Yellowstone Cooke City
Snowfall early this week combined with strong winds created wind slabs, the primary avalanche problem today. These wind slabs should be much less sensitive to triggering than they were a few days ago, but I doubt they have bonded to the underlying snow enough to trust them in high consequence terrain.
In many places, faceted snow exists near the ground but is weak in only a few areas. Ace Powder Guides investigated the snowpack on Mt. Hebgen yesterday near West Yellowstone. They found some faceted crystals but these facets did not propagate cracks in extended column tests. What does this mean? Watch a video from the National Avalanche Center here. We have gotten similar results in many other areas.
One concern I have is the combination of a stiff wind slab resting on weak facets. A recent avalanche was spotted near the summit of Sacajawea likely involving this combination. The Big Sky Ski Patrol also found this combination in a few upper elevation, north facing slopes. I suspect it might be found in other isolated areas like the west side of the Bridger Range where a snowboarder was killed two winters ago in this exact scenario following several days of strong south winds.
For today, the presence of wind slabs that are several days old and isolated slopes that harbor weak faceted snow means human triggered avalanches are possible. For this reason the avalanche danger is rated MODERATE.
I will issue the next advisory tomorrow morning at 7:30 a.m. If you have any snowpack or avalanche observations drop us a line at mtavalanche@gmail.com or call us at 587-6984.
Free 1-hour Avalanche Awareness lecture at Bridger Bowl at 1 p.m. on the 4th floor of the Saddle Peak Lodge this Sunday, December 23. No registration necessary.