Avalanche control results in Yoho today showed that conditions are ripe for triggering in steep alpine and treeline wind affected terrain.
10-25 cms yesterday added to the previous windslabs in alpine and treeline terrain. In some areas, these have been enough to initiate deeper layers in the snowpack once triggered.
This problem represents both the Dec. 2nd crust/ facet layer (treeline and below) and layers of faceted snow that were formed during the late December cold snap (all elevations). If triggered, either layer will result in large avalanches.
Wednesday looks to be cold (lows of -20 to -25 at treeline) and clear with moderate NW alpine winds gradually increasing to strong by the evening. On Thursday, a small system is forecast to bring 5-10 cms of snow with strong W alpine winds and freezing levels staying below 1000m. Friday looks to be overcast with moderate NW winds and light snow.
10-15 cms of low density snow with little wind effect sits on top of windslabs in the alpine and in some treeline areas. These overlie facets in many places, producing moderate to hard test results. The Dec. 2 crust/facets are ~130 cm deep in thicker parts, and half that depth in thinner snowpack areas such as Mt. Stephen and Mt. Dennis.
Observations from a flight showed evidence of a small avalanche cycle to size 2 that had occurred overnight. Avalanche control in Yoho today produced slabs with every shot. Most were failing on a windslab or facet layer 40-60cm deep and then entraining facets in the track. One stepped down to the November facets ~ 180 cm deep.
