Intense winds continue to drive the avalanche danger. Persistent slab problems deeper in the snowpack still can't be written off.
Weather Forecast
Sunday night: Scattered flurries bringing 2-5 cm of new snow. Strong southwest winds. Monday: A mix of sun and cloud with isolated flurries and a trace of new snow. Moderate southwest winds. Alpine high temperatures around -8.Tuesday: Mainly cloudy. Moderate to strong southwest winds. Alpine high temperatures of -7.Wednesday: Mainly cloudy with scattered flurries and a trace to 3 cm of new snow, continuing overnight. Strong southwest winds. Freezing level rising to 1600 metres with alpine high temperatures of -3.
Avalanche Summary
Reports from Saturday showed explosives control in the Castle area producing several Size 2-2.5 storm slabs around 40 cm deep. Ski cutting in the same area produced numerous smaller (Size 1) releases also confined to the recent storm snow.Looking forward, expect ongoing strong winds to promote lee loading as well as slab formation and reactivity even as snowfall tapers off.
Snowpack Summary
Up to 40 cm of new snow from recent stormy weather has buried both a new layer of feathery surface hoar in sheltered areas as well as sun crust on solar aspects. The new snow will need time to form a reliable bond to this previous surface. Moderate to strong winds have also been encouraging slab formation at higher elevations and continuously loading loose snow into deeper wind slabs in lee areas. Beneath the new snow, Previous southwest winds formed wind slabs that are now buried in lee terrain at higher elevations.Down about 60-80 cm, weak layer of feathery surface hoar crystals and/or sun crust from mid-December is found at treeline and below treeline elevations. Deeper in the snowpack, another weak early-season layer of rain crust and sugary facets exists. Slabs may still fail on these layers under the weight of a person, a machine, or large wind slab release. Although the snowpack structure is variable across the region, these persistent slab problems are generally widespread. Snowpack depths are across the region are similarly variable, but typically shallower in the east.
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.