24-25

On Tuesday, January 19, 2016, a Yellowstone Club (YC) Ski Patroller triggered an avalanche on a wind-loaded slope which released on his second turn. The slide broke 2-4 feet deep, 300 feet wide and carried him through a terrain trap of thick trees. He was partially buried 300 vertical feet below in the toe of the debris. His partners reached him within three minutes, but the trauma was fatal.

USFS Snow rangers commuting to and from West Yellowstone noticed a human-triggered avalanche across the Gallatin River from Bacon Rind. Photo: K. Marvinney

USFS Snow rangers commuting to and from West Yellowstone noticed a human-triggered avalanche across the Gallatin River from Bacon Rind. Photo: K. Marvinney

We rode into Portal Creek to the ridgeline above Hidden Lakes and back below Windy Pass. During our ride, we noted no avalanche activity or signs of instability. We dug twice to the ground. Once above Hidden Lakes and once in the corner of an avalanche path below Windy Pass. 

Bottom Line: 

• The snowpack is DEEP. The measured HS was "1 Dave" or 6'5" (200 cm).
• Stability is looking good in our pits, and we are optimistic. 
• ECTNs-mid teens within the layers of the post-Christmas storm snow. 
• Faceted snow near the base of the snowpack is hardening and rounding. Even with extra prodding (deep taps and an unofficial cross-slope PST), we couldn't get it to break or propagate failure.
• The mountain range is expansive, and one must assume spatial variability on both slope and certainly the range scale, but this is good. 

Big Picture: 

• Other than one avalanche that appeared to break on persistent weak layers below Maid of the Mist, Ian and I couldn't think of another persistent slab avalanche in the Northern Gallatin Range. 
• Wind Slab avalanches are the most likely issue.
• Danger is dropping quickly. 
• We don't trust facets often and aren't ready to write off the basal weakness, but triggering an avalanche on these layers seems unlikely for now. 
• This puts wind slab avalanches as the primary concern... and it hasn't been very windy. So, this seems limited for now. 

Terrain Recommendations:

• It is appropriate to consider riding and skiing in avalanche terrain if one is willing to accept the inherent levels of uncertainty involved with steep, backcountry terrain.
• We are pessimistic by nature and like to hedge our bets. The way to do this is by selecting terrain less likely to avalanche (not as steep, more uniform in depth—less rocky, potentially shallow areas, and not wind-loaded) and terrain with lesser consequences (smaller slopes, fewer terrain traps, clean runouts). 

While driving to and from West Yellowstone today, I noticed what is potentially a skier/snowboarder triggered avalanche on the east side of HWY 191 on a West/Southwesterly aspect, directly across the highway from the Bacon Rind Area and Snowslide Creek.  There were numerous tracks through steep rocky chutes next to the road, one of which had avalanched perhaps 75' wide, 18-24" deep, and running nearly to the flats at the base of the slope.  Judging by the thin layer of fresh snow it potentially happened on Sunday or maybe Monday.  There were tracks through the cliffs above the slide and coming out of the slide.