Updated at 9 AM!! Another 40 cm of storm snow overnight. Reactive storm slabs and loose dry avalanches are widespread up to size 2. Increased winds may drive the alpine into HIGH danger.
Weather Forecast
Wednesday: Snow accumulations 5-10 cm with moderate-strong SW winds. Alpine temperatures high of -4.Wednesday night-Thursday: Snow 5-10 cm with strong SW winds. Alpine high of -3 and freezing levels 1100 m. Friday: Snow amounts near 10 cm and moderate ridgetop winds from the SW. Freezing levels rising to 1400 m.
Avalanche Summary
Overnight, new storm snow and winds are causing widespread natural slab avalanches in the Lizard Range.Last week saw several notable deep persistent avalanches including explosive control near Fernie, this avalanche was size 2.5 on a north aspect at 2000 metres, and is believed to have released on the mid-December facets. Last Tuesday a natural avalanche size 3.5 occurred on Mt Hosmer on an East aspect at 2100 metres that appears to have released on, or stepped down to the weak deep persistent layer near the ground. Last Wednesday a size 3.0 avalanche was reported on "Big Steep Mother" bowl on a northeast aspect at 2100 metres. This avalanche appears to have been started by a cornice fall that released a storm slab that then "stepped down" to deeply buried weak facets.
Snowpack Summary
Another 40 cm overnight!! Since Saturday a total of 93 cm of cold, light density storm snow has fallen with little wind effect. This new snow has buried a plethora of old snow surfaces including surface hoar, old wind slab and a sun crust on solar aspects. This new snow also sits on a thick rain crust below 1900 m and a generally well settled snowpack. Isolated basal weaknesses may still exist in shallow snowpack areas. Smaller avalanches may have the potential to step down to those weaker layers waking up the deep persistent slab problem. These weak areas appear to be on north-northeast aspects in the alpine.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.
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.