Be very cautious around steep treeline features where triggering the current persistent slab problem is most likeley.
30 to 50cm of recent snow sits over a facet-crust weak layer combination that is possible to human trigger. Recent observations demonstrate the potential for this problem to be triggered remotely and release sympathetic avalanches in adjacent terrain. It is most reactive around 1900m.
New storm and wind slabs will form throughout the day on Friday. Sensitivity to triggering will be greatest on wind loaded features on east aspects and cross loaded features on north and south aspects. Strong winds mean that wind slab could be found further down slope than expected.
Thursday night: light snow and light to moderate west winds. Low of -4 at 1400m.
Friday: stormy weather with moderate to strong west winds in the alpine. 10 to 30cm of snow expected throughout the day. High of -2 at 1400m.
Saturday: light flurries with moderate northwest winds. Freezing level rising to 1400m.
Sunday: no new snow expected. Moderate southwest winds and freezing levels rising to 1600m.
Over the past few days several skier triggered size 1 and 1.5 avalanches have been reported. We believe these avalanches have been failing on the same layer, a layer of facets on a crust from late January.
On Tuesday, we received report of a large (size 2.5) human-triggered avalanche near Rainbow Mountain that caught and carried a group of five skiers. The avalanche released on a north aspect at 1900m. It broke 40 cm deep and ran on the late January facet-crust layer. The avalanche propagated across adjacent roll-over features and triggered a sympathetic slide on a small feature 200 m away.
New snow accompanied by strong west winds will form new storm and wind slabs on Friday at all elevations.
A layer of facets on a crust is now buried down 30 to 50cm. This layer is widespread at treeline and has produced several human and remote triggered avalanches in the past few days. In sheltered terrain at treeline surface hoar can also be found on this layer.
Deeper in the snowpack, it is possible to find another crust layer buried down 100-200 cm with facets above it from December. This layer is most prominent between 1700-2100 m and is currently classified as dormant; although large loads such as a cornice failure or avalanches in motion may still be able to trigger avalanches on this layer.
