Northern Gallatin

Toured up to the east face of Mt. Blackmore today. We observed two small natural loose dry avalanches occurring right around noon on the new/old snow interface at about 9700' on the E aspect. The largest one ran about 200 feet down into the bowl. 

We observed a hollow snowpack on our ascent and dug a pit at 9600' just below the northeast ridge. We found several weak layers that were fracturing beneath two well-defined crusts. We got a CT2 @ 135cm, CT11 @ 130cm, CT13 @ 118cm, and CT15 @ 115cm; in our extended column test we got ECTP15 Q2 @ 130cm.

Today we toured up above Blackmore Lake to ski a E-NE facing meadow. We observed about 5-10cm of fresh snow in the area with minimal wind loading. On South aspects, the recent sun crust was much more supportable than in more shaded and protected areas. There was evidence of past wind loading at our pit location, which was on a slightly more north-facing ridge than the meadow we skied. Although this recent crust was evident on all aspects, it was quite soft and breakable on protected aspects. An ECT test revealed instability above a crust layer at 130cm in the snowpack (ECTN22@130). The shear quality was clean at this interface and, when the shovel was placed behind the block, it popped off quite easily. With the significant temperature shifts adding some complexity to the snowpack, it will be interesting to see how the stability progresses at these crust interfaces. 

I toured up toward Divide today, mostly just to get out and take a peek at the snowpack. The storm overnight dropped 10-20 cm up high, and it was getting moved around a fair amount by the wind. 
 

I dug my first pit on an east aspect at 8900’. The snow was 165 cm deep here, and there was a visible dark band 20 cm down that was pencil-hard and 1 cm thick. I got an ECTN13 on this, failing on a thin layer of facets just below the harder snow. I also got an ECTN 17 on another thin layer of facets another 20 cm down. When I filled the pit in, the top 20cm readily came off of my extended column, and the rest stayed cohesive to the ground as I tipped it over, save for the rotten stuff at the very bottom of the snowpack. 
 

I dug another pit at 9550’ on the SE aspect of Divide. This one was 145 cm deep and had a similar structure to my first one, and gave me ECTN14 and ECTN18 on what I believe to be the same layers, although the firm band of snow 25 cm down didn’t have as obvious of a layer of low-density facets beneath it. I did get a clean, fast propagation 60 cm down at ECTP22. The slope I was on was only 28 degrees, but I bailed to head home and eat cheesecake instead. 

We found the recently buried weak layer of near-surface facets one foot deep. The sugary facets lower in the snowpack were also present but neither propagated in our stability tests. Thankfully, another group dug a pit nearby. They got an ECTP20 on the near-surface facet layer one foot down. This means the layer is confirmed in Hyalite, Buck Ridge, and Lionhead. A similar story is coming out of the Bridger Range. Until proven otherwise, I am operating with the assumption that it is everywhere from north of Bozeman to Island Park. I am worried about this layer when more snow starts adding up. 

The wind was blowing ~ 20 mph on the ridge and depositions of wind-drifted snow near ridgelines, in cross-loaded gullies and near wind-breaks like trees, cliffs, and outcroppings were the most likely place to trigger a slide today.

Temperatures were above freezing when we got back to the car. Some small, wet-loose snow avalanches slide from road cuts and piled up a few feet deep next to the Hyalite Canyon Road.