It has been tricky this week deciding whether or not to include persistent slab as a problem in our avalanche advisories. Field observations continue to highlight our thin snowpack and poor structure. Numerous large collapses and test results showing propagation potential have been reported from all corners of the range, and these signs of instability are keeping forecaster confidence low. While a weak faceted snowpack has been found throughout the range at all elevations, we cannot point to a specific layer of concern. Rather we are dealing with a variety of facet crust combos and large variability when it comes to slab density and thickness. In isolated high elevation catchment zones, loose facets are underlying a thick, dense wind slab while in many lower elevation areas, we are finding thinner melt-freeze or wind crusts interacting with faceted grains. It is likely that a large load of new snow would initiate a significant avalanche cycle. However, we have not yet received any reports of avalanche activity on these buried weak layers. Given the extreme variability across the landscape, we cannot discount the possibility of isolated areas where an avalanche could be triggered, but in reality, the risk remains low. It is worth noting that large collapsing has been reported at lower elevations where the underlying snowpack is relatively thin. In these areas, shallowly buried rocks and bushes act as trigger points and may aid in the propagation of a weak layer. In times with high uncertainty and large variability, it is advisable to approach objectives with elevated caution and use terrain choice to limit your exposure. Don’t be afraid to dig in and evaluate the underlying snowpack for instabilities and realize that many preseason hazards such as shallowly buried rocks and trees punctuate the landscape.
