Sunny breaks on Sunday could reactivate weaknesses in the snowpack with the potential for very large avalanches.
Confidence
Fair - Timing or intensity of solar radiation is uncertain
Weather Forecast
Synopsis: The remnants of a very weak system pass over the region Saturday afternoon ahead of Sunday's strengthening ridge. A warm system approaches the coast Monday which should push high cloud into the region. There's potential for very high freezing levels on Tuesday, but its still too far out to say. There's a chance for significant precipitation on Wednesday.Sunday: Freezing Level: 900m - 1200m; Precipitation: Trace; Treeline Wind: Very light, Variable | Ridgetop Wind: Light, WestMonday: Freezing Level: 1000m; Precipitation: Nil; Treeline Wind: Light, NE | Ridgetop Wind: Light SWTuesday: Freezing Level: 1600m - 1900m; Precipitation: Trace; Treeline Wind: Light, SW | Ridgetop Wind: Light SW
Avalanche Summary
The Purcell snowpack is a strange beast at the moment. Most of the region reported no avalanche activity for the day, and yet we received reports of a widespread cycle over the last 48 hours to size 2.5 in the mountains west of Kimberely. Sounds like some of the activity was induced by natural cornice fall.We've received reports of size 2.5 and size 3 natural slab avalanches which occurred a few days ago in the Quartz Creek area. The slides occurred on southwest facing alpine terrain with solar warming as a trigger.
Snowpack Summary
Light snow accumulations overlie a well-settled storm slab which formed last weekend. Under the storm slab you'll likely find small surface hoar in shaded terrain and crusts on previously sun-exposed slopes. Recent winds have redistributed surface snow into wind slabs in exposed lee terrain. Rain from the weekend saturated the snowpack at lower elevations and the more recent accumulations may overlie a refrozen crust. Up to 95cm below the surface you may find surface hoar and crusts buried at the beginning of March. This interface is still touchy in some areas, particularly in the north of the region. The deeper facet/crust persistent weakness buried at the beginning of February, now down 60 to 160cm, has been highly variable in terms of reactivity and is still very difficult to trust. Needless to say, any avalanche at these deeper, persistent interfaces would be large and destructive.Weak basal facets exist in many areas, but without a large load, triggering now is unlikely.
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.
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.