Southern Gallatin

We got to ride into Tepee Basin with a pair of snowmobilers who were involved in an avalanche two days ago (2/23). The pair generously offered to join us and run us through the incident. It was an incredible opportunity to learn from each other. Read details about the slide.

The avalanche failed on the weak layer of facets that formed in late January. We also spotted another avalanche in similar, mid-elevation terrain likely triggered yesterday or earlier this morning. Both of these avalanches fit the pattern we've been seeing in Lionhead and the recent slide outside the forecast area in the Black Canyon area of Island Park. Other than the Black Canyon avalanche which is uncertain because we have not visited the site, the slides are taking place in mid-elevation terrain, smaller slopes with minimal wind-loading, and a thinner snowpack. 

The snowpack in both the Tepee slides was thin relative to the average snowpack depth (129 cm). 

Take Homes:

1. You aren't good to go if you avoid the steep, upper-elevation, wind-loaded bowls. Steep slopes at mid-elevations harbor weak snow and have the potential for an avalanche. 
2. The persistent slab avalanche problem is alive and well. The epicenter of this problem is in the Lionhead area and the Southern Madison and Southern Gallatin Ranges. 
3. The issue with this avalanche problem is the distribution. It's nearly impossible to tell which slopes will slide and which ones won't. On many, the weak layer isn't so weak and the likelihood of triggering one is low. On other slopes, the weak layer is very weak and the likelihood of triggering one is up there. 

Found moist snow that was starting to freeze on solar's in Hyalite at 8000' Friday. Went searching for better conditions up Specimen Creek today. The snow quality was much better at similar aspects and elevations. Northerly aspects stayed dry in both zones but I was curious about the difference in the two advisory areas. Looking at temps from weather stations the southern range has been 10f to 15f degrees cooler. 

Stability was much different as well. In Hyalite, the nsf layer that was formed in late January, looked to be rounding and didn't produce propagating results or clean shears. Up Specimen I had an ECTP15 and a CT15 Q1 on the same layer. This certainly aligns with the forecast. 

On a ridge up Specimen, winds were moderate from the SW and shifted SE in the evening. I did find thin reactive wind slabs and cracking in fresh drifts. Wind was actively transporting on the ridge. I felt wind loaded slopes had the greatest potential to slide since sheltered slopes only had a 25cm slab over the weak layer but I  avoided avalanche terrain regardless. 

We toured into Specimen Creek today and rode on E-SE and W aspects. Though more snow exists in this location than is typical, the snowpack here is still shallow and weak.

Our snow profile on a W aspect at 8100' showed us some of the weakest snow structure we had seen this season. Sugary, large-grained facets and depth hoar spilled out of the pit wall at the ground. In this location, a 6" slab sits atop this weak snow, but was not cohesive enough to get unstable test results (HS: 90, ECTX). 

Outside of very weak structure, no other signs of instability like cracking, collapsing or recent avalanches were spotted. 

While the state of the snowpack now provides better coverage and riding than usual, expect to see a jump in avalanche danger on these shallow, weak slopes when/if they receive another good round of snowfall.