Alpine temperatures rising to 0 degrees, more snow and wind is driving the danger rating to HIGH.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Friday: Snow amounts 10-20 cm by Friday afternoon. Ridgetop winds light with gusts up to 80 km/hr from the SW. Alpine temperatures near 0 and freezing levels rising to 1400 m by the afternoon. Saturday: Snow amounts 10-20 cm overnight Friday and tapering off Saturday. Confidence remains low in actual amounts and timing. Rigetop winds gusting to 75 km/hr from the SW. Alpine temperatures near -1 and freezing levels 1200 m. Sunday: Unsettled conditions with a trace. Ridgetop winds generally light from the SW and freezing levels falling to 1100 m.
Avalanche Summary
Numerous explosive results up to size 1.5 were reported from the Lizard Range on Thursday. Loose dry avalanches were also noted from steeper terrain features at treeline and below. On Friday, alpine temperatures are expected to rise to 0 degrees with more forecast snow and wind. This recipe may create an upside down feel to the snowpack (denser slab). I suspect if the weather forecast is accurate we'll see another round of natural slab avalanches. This is also driving the danger ratings to HIGH.
Snowpack Summary
A metre of low density storm snow has fallen in the past week burying a variety of old now surfaces including surface hoar, facets (sugary snow), stiff wind slabs, sun crust on solar aspects and a widespread rain crust below 1900 m. The recent storm snow is reportedly showing a poor bond to these older snow surfaces. Strong winds from the SW are likely transporting the new snow onto leeward slopes, building thicker and stiffer slabs and promoting large cornice growth. Isolated basal weaknesses may still exist in shallow snowpack areas. 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.