Regions
Northwest Coastal.
Confidence
Fair - Due to variable weather conditions
Weather Forecast
Monday: Light S winds, with moderate to strong NE outflow winds in places. Alpine temperatures around -11 with an inversion (colder temperatures in the valley floor). No precipitation.Tuesday: Light winds. Alpine temperature around -9 with an inversion. No precipitation.Wednesday: Light S winds. Alpine temperature around -10. No precipitation.
Avalanche Summary
On Saturday, several natural size 1-2 loose dry and thin slab avalanches failed in steep isolated terrain features wind-loaded by outflow (down-valley) winds. Explosives triggered size 2-3 slabs which failed near the ground in facets. Near Bear Pass, natural ice fall triggered size 2.5 and 3 loose snow avalanches, entraining old storm snow.
Snowpack Summary
Wind slabs and cornices have developed on a fairly widespread basis and may be found in unusual locations lee to NE and E outflow winds. Surface faceting is likely to continue while the weather remains cold. A layer of surface hoar buried in the upper metre of the pack has been observed in the Shames backcountry. The midpack is generally well settled. Near the base of the snowpack, a crust/facet layer continues to give hard, sudden results in snowpack tests. This weakness is unlikely to be triggered by a single person, but it remains possible with a very heavy load (e.g. cornice fall) or from a thin-spot trigger point.
Problems
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
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.