Regions
South Coast Inland.
Progressive storm loading and a buried weak layer have created tricky conditions. Watch for fresh wind slabs on Thursday and use extra caution on south facing slopes when the sun is out. Conservative terrain selection remains critical.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Another 5-15 cm of snow is expected Wednesday overnight with more expected in the south than the north. Mainly cloudy conditions are expected on Thursday with light snow flurries and sunny breaks both possible. Alpine wind is expected to be moderate from the southwest and treeline temperatures are forecast to reach around -6C. A storm system is expected to reach the region Thursday evening. 20-30 cm of snow is forecast between Thursday evening and Friday afternoon. Alpine wind is forecast to be strong from the southwest and freezing levels may climb as high as 1600 m. The next storm system is currently forecast to arrive on Saturday afternoon or evening.
Avalanche Summary
On Tuesday morning, solar trigger sluffing was reported in the Coquihalla. In the north of the region, the top 10-20 cm was reported to be sluffing easily in steep terrain. On Monday, explosives triggered three size 2.5 slab avalanches in the Duffey area which released on late-February sun crust down 40-50 cm. These were on southeast through southwest aspects at 2000-2200 m elevation. Extensive whumphing was also reported in the north of the region on Monday.On Thursday, large persistent slab avalanches remain a concern for the accumulated snow from the past week releasing on the February weak layers. It may still be possible for a person to directly trigger a persistent slab or a smaller avalanche could step down. Recent strong southwest wind has created new wind slabs in immediately leeward terrain features which are expected to remain touchy on Thursday.
Snowpack Summary
Another 10-20 cm on Tuesday brings the typical storm accumulation in the past week to 50-70 cm in the north of the region and to over 1 m in the south of the region. Strong south and southwest wind during the storm redistributed much of this snow in wind-exposed terrain forming thick wind slabs. The new snow overlies the mid-February and late-February interfaces which may be close together in the snowpack. The late-February interface consists of wind affected surfaces in exposed terrain, sun crust on steep solar aspects, and facets and surface hoar in sheltered areas. The mid-February interface consists of a thick rain crust which extends to at least treeline, a sun crust on steep solar aspects, and in many places, a layer of facets overlying the crust. Recent observations suggest the late-February layer is most reactive in the north of region and the mid-February layer is most reactive in the south of the region. Below these layers, the mid and lower snowpack are generally well settled and strong.
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.
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.