Danger will increase this week as snow and strong winds are expected to start on Thursday afternoon.
Confidence
Moderate - Intensity of incoming weather systems is uncertain
Weather Forecast
THURSDAY: Cloudy with flurries starting in the afternoon, strong west winds, treeline temperatures around -15 C.FRIDAY: 10-20 cm of low density snow, strong west winds, treeline temperatures around -17 C.SATURDAY: Another pulse of snow with 10-30 cm possible, strong west winds, treeline temperatures around -20 C.
Avalanche Summary
No recent avalanches have been reported. On Monday, one large naturally-triggered avalanche (size 2) was reported on a north-facing alpine feature that likely failed on the mid-December surface hoar layer. There have been some isolated reports of whumpfs at small avalanches failing on the mid-December surface hoar layer, but in most areas the snow above this layer has not settled into a slab yet.
Snowpack Summary
Cold temperatures are preserving roughly 50 cm of low density snow from last week's storms. The snow is being deposited into harder wind slabs in exposed terrain, but remains low density in sheltered areas. The main question in the snowpack surrounds the mid-December layer buried 50 cm below the surface. The layer includes crusts on south and west facing slopes and feathery surface hoar in sheltered areas at and below treeline. The distribution of the layer, as well as the properties of the snow above it, is variable. The most suspect areas are where the wind has formed stiff slabs above the layer and on slopes with preserved surface hoar. The lower snowpack is generally well settled with a thick prominent crust that was buried near the end of November.
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.