While Wind Slab predominates , uncertainty exists about the sensitivity of buried weak layers - a cautious approach is recommended at Alpine and Treeline elevations.
Weather Forecast
A mix of sun and cloud with isolated flurries daily. Freezing levels will hover around valley floor, rising slightly higher by Wednesday. Ridge winds are forecast at Moderate from the W-SW, rising to strong by Wednesday.
Snowpack Summary
15cm of new fluff sits on Fridays' Rain Crust below 2100m, and on thick, dense Wind Slabs above this. Forecast wind will build new wind slabs in lees. The primary concern, though, are old Wind Slabs. These may propagate widely, especially if they initiate on/step down to a weak layer buried 40-80cm: Crust on solar aspects, Surface Hoar on shady.
Avalanche Summary
Two large Slab avalanches were observed today on lee N-E aspects, initiating around 2300m. These are likely Wind Slabs, but could be on the Jan 4 Surface Hoar. Earlier, a widespread natural cycle of small avalanches was observed during Fridays warm storm, with a few isolated large avalanches. One of these was a persistent slab on the Jan 4 crust.
Confidence
Due to the number and quality of field observations on Sunday
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.