This past week I have focused on aspects facing due west and east where I have been finding a widespread PWL at the mid and upper elevations. On slopes with a stronger slab, I have been getting full propagation with extended column tests, generally failing in fewer than 20 taps (ECTP 20 and less). On one east-facing aspect at 10,200 with a strong1F-hard wind slab on top of a faceted layer, I got ECTPV (collapse and propagation upon isolation), indicating a very dangerous structure (photo below). Other pits nearby were ECTP17 and ECTP21 and this just reflects the widespread spatial variability of our snowpack.

In general, it seems you need a stronger 1F-hard slab on top of the facets, but I've seen evidence where the slab is only 4F hard, but I'm also getting full propagation with extended column tests. The avalanche off of Rocky Point only had a 4F hard slab on top of an exceptionally weak layer of facets, so it seems that in some places, all you need is a slab that is "strong enough" to avalanche.

When assigning a danger rating for an avalanche forecast, the forecaster typically has a level of confidence in the information they have available (wind, snowfall, water, snowpack history, recent avalanches, etc.) to assign a danger rating. I have a lower level of confidence in forecasting the avalanche danger for our PWL problem. Yes, the PWL is widespread at the mid and upper elevations on aspects facing west through north and east, and it seems you need a stronger slab on top of the facets to create an avalanche, but in some places, the slab doesn't have to be especially strong. Warm temperatures this past week have helped the snowpack stabilize, and this is a good thing, but it only adds to the complexity where it now may be harder to trigger an avalanche on some slopes. It also may allow the snowpack to support more of a load before avalanching. Over the past 10 days, we've had loading events from snowfall, and especially wind drifting. Some of these events have created a spike in avalanches (Sunday, December 15 had six avalanches reported), but we haven't gone through a significant avalanche cycle. Yet. At some point, our weak snowpack will reach a tipping point; I have a high level of confidence in that occurring; I have a lower level of confidence in when.