Take a look at these graphics:
The top chart is from Bruce Tremper’s Staying Alive in Avalanche Terrain.
The top chart shows the timeline of stabilization after a storm event on different weak layers. Storm snow instabilities tend to stabilize quickly after the storm and slabs on persistent weak layer take longer to stabilize.
The bottom chart is modified from Bruce Tremper’s Staying Alive in Avalanche Terrain. It shows avalanche activity with storms throughout the winter on a persistent weak layer. With smaller storms, avalanche activity increases with each storm, then drops off. But, the persistent problem does not disappear and the slab continues to build up with each storm. At some point the slab may be built up so a storm tips the balance and we see avalanches to deeper persistent weak layers.
Here in the Tetons, we have a widely variable snowpack with persistent weak layers of facets and buried surface hoar. In certain areas, the snowpack structure is quite poor. We have had several storms in the past two weeks and have seen storm and wind slab avalanche activity during these storms. We have also seen two fatalities from persistent slab avalanches. In many places, the slab has not been built up quickly or deep enough to see additional persistent slab avalanches. As we have more storms and loading, the question I am asking is, “Is there enough loading to see larger avalanches into the deeper weak layers?”
The snowpack is variable and it is uncertain what type of avalanches we’ll see with subsequent storms. Below are two videos from January 1st 2014 that show differing results in stability tests. But, both pits show the same poor structure that could be a big problem if we get a significant loading event.