Sweeney Peak

Old wind slabs from strong winds and snow this week have become stubborn, but smaller fresh wind slabs were growing today, and I observed one fresh natural wind slab on an upper elevation southeast aspect. Cornices at upper elevations are large and overhanging. The crust facet persistent weak layer is now buried nearly 3 feet deep and has become unlikely to trigger. However, if you were to trigger an avalanche on that layer, it would be large and consequential.  

I observed signs of instability like cracking in newly wind drifted snow and stubborn old cornices and drifts, including one small fresh natural wind slab on an upper elevation southeast aspect.

I returned to Sweeney today to look at how things have changed over the last week. I was last out here a week ago, on Friday, February 23rd. Since then, we have had a prolonged period of strong southwest winds, with some significant snowfall. The highest elevations, above around 8500 ft are heavily wind affected with wind board along ridgelines and southwest aspects wind scoured to the rocks. I suspect a significant amount of snow was simply blown away and sublimated. However, there has been significant wind loading and cornice development on north and east aspects at upper elevations. Although they were somewhat stubborn to trigger, some cornices are large and overhanging. I observed one natural D1.5 wind slab avalanche on a northeast aspect at 8200 ft that likely occurred a few days ago from a natural cornice failure. Today, the old and hard wind slabs that developed over the week were stubborn to unreactive. However, fresher wind slabs from last night's snowfall and ongoing southwest winds were sensitive at the highest elevations today. 

There was around 1" of new snow from last night at 5000 ft and 3" at 6000 ft. The new snow was resting on a melt freeze crust at most lower and middle elevations. At upper elevations, it was difficult to tell exactly how much new snow there was because of wind drifting and the strong winds at the beginning of last night's storm. There was around 6" of lower density snow resting on harder, wind affected snow in most places. That lower density snow was getting transported onto north and east aspects, especially above 8000 ft. I observed one small fresh natural wind slab on a southeast aspect at 8900 ft. 

I dug a snowpit on a northeast aspect at 7900 ft, near where I dug a snowpit a week ago. There was around 55 cm of new snow from the last week - my snowpit from a week ago was fully buried. I found the same crust facet layer now buried nearly a meter deep (~3 feet). It has become more stubborn to trigger and did not fail in an extended column test. However, it produced an unstable result in a propagation saw test, showing that it still has the potential to propagate if triggered (PST 30/100 End). I did not observe any other signs of instability, like cracking or collapsing on persistent weak layers. It seems the likelihood of triggering a persistent slab is now unlikely, but the consequences remain high. Facets near the ground continue to round, but are still weak and only fist hard in places. An extended column test produced a non-propagating result below an old wind slab at the interface below this week's snowfall (ECTN 24, 55 cm deep).