New snow and wind have created fresh wind slabs that are ripe for human triggering.
Confidence
Low - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Expecting 5-10cm of snow Friday and another 5-10cm on Saturday. This will be accompanied by moderate to strong southwesterly winds and rising freezing levels to around 1300m. Things cool off and dry out on Sunday.
Avalanche Summary
No new avalanche observations from Wednesday, but we expect human triggered avalanches to occur on Thursday due to new snow and wind.
Snowpack Summary
10-20cm of new snow overnight with light to moderate southwesterly winds have created fresh wind slabs ripe for human triggering in the alpine and exposed treeline. A persistent weak layer of buried surface hoar can be found at variable depths depending on elevation. For example our field team found it down 45 cm at 1850 meters and down 90 cm at 2150 meters in the Crown Mountain area, where compression tests gave hard sudden planar results. A weak crust/facet layer from early-December can typically be found down over 1m. It has become difficult to trigger this layer but it is still reactive in snowpack tests suggesting that it remains capable of wide propagations and large destructive avalanches. Below 1700m the most recent snow hides a melt-freeze crust.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.