Avalanche Forecast

Moderate -

Friday night: Cloudy with scattered flurries bringing 3-6 cm of new snow, with rain below about 1100 metres. Strong to extreme west winds.Saturday: Cloudy with continuing flurries bringing a trace to 5 cm of new snow. Light rain below about 1100 metres. Strong to extreme west or southwest winds. Alpine high temperatures around -1 with freezing levels around 1500 metres.Sunday: Mainly sunny. Moderate north winds easing to light over the day. Alpine high temperatures around -6 with freezing levels to 700 metres.Monday: Sunny with increasing cloud. Light variable winds. Alpine high temperatures around -1 under an alpine temperature inversion.

A large (size 2.5) storm slab avalanche was triggered remotely (from 20 metres away) by a skier in the Howson Range on Tuesday. This occurred on a southwest aspect at 1700 metres and the slab had a depth of about 30 cm. It is likely that the failure plane in this slide was some variation on the surface hoar and crust combination described in our snowpack summary. This weak layer is one of our primary concerns in the region and can be expected to produce human-triggered avalanches in areas where the overlying new snow has settled into a slab.Looking forward, continued warm temperatures, snowfall, and wind loading may promote similar avalanche activity over this surface hoar/crust combination layer. Higher elevations will more likely see the formation of thin new wind slabs, with the likelihood of avalanches over our surface hoar layer more limited to protected areas where surface hoar may be preserved.

Light snowfall and strong winds are expected to form a new surface of wind-affected snow by Saturday morning.  Beneath the evolving surface, we have around 30 cm of newly wind-affected snow from snowfall earlier in the week. A thin crust may be found within this layer.At alpine and high treeline elevations, this recent snow sits on old wind-affected and faceted snow, and possibly over a weak layer of surface hoar in more protected areas. The recent snow sits on a rain crust/surface hoar combination below about 1600 m. This weak interface is one of our primary avalanche problems, particularly as wind and warming have worked to transform the overlying snow into a more cohesive slab..Under the interface described above, the mid snowpack is generally strong. Faceted (sugary snow) is present in this part of the snowpack, but the overall dense structure here helps to overcome the weakness of these grains.The bottom 30 to 50 cm of the snowpack consists of a weak layering of facets and crusts, particularly in areas where the snowpack is thin. It may be possible for large slab avalanches to step down down to ground in these thin snowpack areas, resulting in even larger avalanches.