Widespread natural avalanches are expected to continue today, running into the avalanche path run-outs. Conservative terrain selection, and avoiding exposure to overhead avalanche terrain is recommended.
Weather Forecast
Thursday expect another 15cm of snow, moderate to strong SW winds and freezing levels rising to 1700m. Overnight and into Friday freezing levels will drop, alpine temps are expected to lower to -8'C, and the snow will taper off. Saturday expect flurries to accumulate to another 7cm, with gusty SW winds at ridgetop.
Snowpack Summary
Up to 20 cm of new snow fell overnight, with temps just below 0 up to 1900m. The new snow is expected to settle rapidly with the mild temps into a slab. The new snow hides variable wind-effected snow in the alpine and soft slab at tree-line and below. Whumphing and cracking on the Jan 4 weak layer, now buried 50-80cm, is still being reported.
Avalanche Summary
A natural avalanche cycle is occurring as I type, with numerous size 2.5-3 avalanches occurring overnight. They occurred from all aspects, and some avalanches triggered deeper slabs at lower elevations on the avalanche fans. Yesterday numerous size 2-3 natural avalanches were triggered by windloading.
Problems
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.
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.
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.