Regions
Northwest Coastal.
An persistent weak layer buried earlier this month has woken up. The consequences of triggering this layer could be very high. Time to step back and stick to supported terrain.
Weather Forecast
Thursday: Cloudy with flurries bringing 10-15 cm of new snow, continuing overnight. Moderate to strong south winds. Freezing level to 700 metres with alpine high temperatures around -4.Friday: Mainly cloudy with continuing isolated flurries and a trace of new snow. Light northwest winds. Freezing level to 700 metres with alpine high temperatures around -5.Saturday: A mix of sun and cloud. Light southeast winds. Freezing level to 800 metres with alpine high temperatures around - 3.
Avalanche Summary
Reports from Tuesday showed numerous large (size 2-3) persistent slabs releasing with remote (from a distance) triggering over a layer of surface hoar buried 40-60 cm deep in the Terrace area. This activity was focused on shaded aspects at treeline and below.There was a report of a small (size 1) skier-triggered storm slab on Sunday that occurred on a north aspect at 1400 metres. The slab was 40 cm deep and failed on a more recently buried layer of surface hoar. Numerous natural wind slab and storm slab releases from size 1.5-2.5 were observed from the highway in Bear Pass. Poor visibility had been noted for limiting observations throughout the region.Reports from Saturday showed ski cutting in the Bear Pass area producing both slab and loose dry avalanches to size 1.5. Slabs failed all the way down to the melt-freeze crust buried 60 cm deep at treeline on north aspects.
Snowpack Summary
Stormy weather brought 50-80 cm of new snow to the region over the past week. These accumulations taper quickly at lower elevations as well as moving inland from the coast. Strong southwest to northwest winds have been redistributing the new snow into wind slabs at high elevations. Beneath the wind effect, the storm snow overlies old surfaces that include a layer of surface hoar on high shaded aspects as well as a melt-freeze crust on all aspects at treeline and below. Another lingering layer of surface hoar can be found just below the first on shaded aspects at lower elevations. With the overlying storm snow now settled into a stiffer slab, this layer became touchy in the Terrace area on Tuesday, producing numerous large, remotely-triggered avalanches. Deeper in the mid-pack, layers of crusts, facets, and isolated surface hoar buried 50 to 100 cm exist from mid- and late-February and a surface hoar/ crust layer from January is buried around 150 to 200 cm. Near the bottom of the snowpack, sugary facets exist in colder and dryer parts of the region, such as the far north. These buried layers are currently dormant.
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.