22-23

On January 19 we rode north of Cooke City to dig in a variety of locations and look for the surface hoar layer that is buried 1-2 feet deep. Over the past week, forecasters and other groups have found unstable test scores on this layer, and there was at least one rider triggered avalanche and one natural avalanche that broke on this layer 3-5 days ago. These two known avalanches were on east to northeast aspects at 9,200-9,800'.

We dug five snowpits and performed extended column tests in each on 1/19/23 (I said "four pits" in the attached video, but I forgot to count one that was 15 feet away from another). Four snowpits were on northeast to north facing slopes between 9,200-10,000', and one pit was on a southwest facing slope at 9,200'. In one pit on a NE aspect at 9,200' we had an ECTP 15 on the surface hoar 35 cm below the surface. In all other pits we had ECTN14-19 at the depth of the surface hoar, and no obvious feathery crystals were visible. The layers where the ECTNs broke appeared to be decomposing, preserved dendrites or maybe decomposing surface hoar.

There was about 6" of low density snow that slowly accumulated over the last few days. Below and within this new snow are layers of near surface facets and surface hoar that formed during clear, cold nights. These may be future weak layers. There was almost no wind the last 3-4+ days, so this snow is still available to be drifted into thick slabs when the wind increases.

We stopped on a couple west facing slopes that were heavily wind-affected, and we sunk about 3 feet to the ground when we got off our sleds. These areas of shallow snow hold very weak, sugary facets that will be a problem if loaded with heavy snowfall.

At the moment, the general snowpack stability is improving with an extended break from heavy snow or wind-loading. I suspect there are a few lingering pockets of unstable surface hoar that could be triggered, and there is plenty of weak snow near the surface. If the wind blows snow into thick drifts, or more snow falls than expected, stability could quickly become worse.

Photos of avalanches are those previously reported on Monday on Miller (photo taken 1/18) and Henderson (taken 1/17).

Region

Cooke City

Location (from list)

COOKE CITY

Observer Name

Alex Marienthal

Looking for surface hoar, Cooke City - 19 Jan 2023

Read more about Looking for surface hoar, Cooke City - 19 Jan 2023

Read more about Natural avalanche in Lionhead

A natural slide in the back bowls of Lionhead.

Forecast link: GNFAC Avalanche Forecast for Sat Jan 21, 2023 GNFAC Avalanche Forecast for Mon Jan 23, 2023 GNFAC Avalanche Forecast for Wed Jan 25, 2023

Lionhead Range, 2023-01-19

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GNFAC Avalanche Forecast for Thu Jan 19, 2023

Snowpack and Avalanche Discussion

Another disaster was averted on Saddle Peak yesterday. A snowboarder triggered a slide right outside Bridger Bowl’s boundary on the Football field on Saddle Peak. The slide ran over the cliffs which would be fatal. The snowboarder shared a <a href="https://youtu.be/w9COKhySd8o">…; and sent in an <a href="https://www.mtavalanche.com/node/27715"><span…;. The video is worth watching. The slide was 6” deep (estimated) and involved wind-drifted snow that was blown into slabs the night before. A natural slide in Argentina bowl (<a href="https://www.mtavalanche.com/images/23/shallow-avalanche-argentina-bowl"…;) and <a href="https://www.mtavalanche.com/node/27718"><span… triggering small, thin slabs in Hyalite</a> round out yesterday’s activity. The day before on Ross Peak skiers got poor test scores on weak, sugary snow near the ground (<a href="https://www.mtavalanche.com/node/27697"><span…;). They backed off their objective.

In the last 13 days it has snowed 4 days of 2” each; not much. People are starting to stretch their legs and feel confident, which is not unreasonable. Yet avalanche potential exists and we cannot forget this. Besides thinking about your own safety, be aware that people below you are victims of your indescretion. We have weak snow at the ground that is reactive in stability tests and could avalanche. We also have a few wind slabs, most likely found at the ridges. Dig, test, ski one at a time and always think, “What if?” What if I’m wrong? What if someone is below me? What if I can’t see my partner? Have a plan.

For today the avalanche danger is rated MODERATE on all slopes.

Yesterday, a snowmobiler was caught in a small slide on Two Top south of West Yellowstone (<a href="https://www.mtavalanche.com/node/27717"><span… and pics</a>). He was ok. Also yesterday, Dave and I rode into Lionhead and saw a few natural avalanches and one small snowmobiler triggered slide (<a href="https://www.mtavalanche.com/node/27740"><span… and pics</a>). Our main concern is a weak layer of feathery surface hoar and/or a thin layer of sugary, small-grained facets buried 1-2 feet deep. We hunted for this layer and made a <a href="https://youtu.be/ibAh34muOQc">…;. In one instance a loose snow slide triggered a deeper slab, which is similar to what a skier saw on Woody Ridge outside Cooke City yesterday (<a href="http://www.mtavalanche.com/images/23/woody-ridge-natural"><…;). Further north the Yellowstone Club Ski Patrol took a picture of a recent natural slab avalanche near Buck Ridge, more evidence that this weak layer has not healed. <a href="https://youtu.be/TV7IXE41Skg">…’s video</a> from Hebgen on traveling in terrain with a buried weak layer and <a href="https://youtu.be/jQg8gqFqn1M">…’s video</a> from Beehive Basin where he also found surface hoar are instructive on what to do while riding or skiing in the backcountry. You can either avoid all avalanche terrain or do your homework by digging and testing, looking for unstable snow. Avalanches right now are acting like insurgents, striking when we least expect it.

For today, the avalanche danger is rated MODERATE on all slopes.

Read more about GNFAC Avalanche Forecast for Thu Jan 19, 2023

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Read more about Natural slides, Lionhead

Dave and Doug rode around and saw multiple natural and 1 sledder triggered slide on Lionhead. Some were thin and just involved news snow and others were deeper and broke on the buried surface hoar layer.