Persistent slab avalanches continue to be triggered by humans. The consequence of being involved with one is high.
Weather Forecast
SATURDAY NIGHT: Mostly cloudy with isolated snowfall, trace accumulation, light to moderate northeast wind, alpine temperature -13 C.SUNDAY: Mostly clear skies, moderate northeast wind, alpine temperature -16 C.MONDAY: Mix of sun and cloud, light to moderate west wind, alpine temperature -15 C.TUESDAY: Cloudy with light snowfall, accumulation 1 to 5 cm, moderate west wind, alpine temperature -14 C.
Avalanche Summary
Two small to large (size 1 to 2) persistent slab avalanches were triggered by skiers on Friday. They were 50 to 70 cm deep and released on the mid-January surface hoar layer described in the Snowpack Summary. The occurred at treeline and alpine elevations on north to northwest aspects.
Snowpack Summary
Recent strong northeast wind has blown loose snow into wind slabs in exposed areas.A touchy weak layer responsible for surprise avalanches and several close calls lies approximately 30 cm below the surface in shallow snowpack areas and 60 cm or more in deeper areas. This weak layer of surface hoar and faceted grains was buried mid-January. On southerly aspects, it lies on top of a melt-freeze crust. It is most prevalent at treeline and below treeline elevations, but there have been a few reports of its presence in sheltered areas in the alpine. This layer is shallow enough to be triggered but deep enough to produce large avalanches.Deeper layers in the snowpack are not a factor at this time.
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.