Sunny breaks on Monday could reactivate weaknesses in the snowpack with the potential for very large natural avalanches.
Confidence
Fair - Freezing levels are uncertain on Tuesday
Weather Forecast
Synopsis: An upper ridge passes over the region Monday ahead of a pacific frontal system that should force the freezing level to rise under cloudy skies Tuesday. The warming will likely be most dramatic over the Southern Purcells. Look for some precipitation on Wednesday.Monday: Freezing Level: 1000m -1300m; Precipitation: Trace; Treeline Wind: Light, NE | Ridgetop Wind: Light, WTuesday: Freezing Level: 1700m - 2200m; Precipitation: 0:5mm - 0:5cm; Treeline Wind: Light, S | Ridgetop Wind: Moderate, SW Wednesday: Freezing Level: 900m - 1200m; Precipitation: 3:10mm - 4:15cm; Treeline Wind: Light, NE | Ridgetop Wind: Moderate, SW
Avalanche Summary
The Purcell snowpack is a strange beast at the moment:On Saturday an anomalous sized 3.5 avalanche released naturally out of a SE facing feature at 2700m in the central portion of the region. No other activity was reported on Saturday.On Friday while most of the region reported no avalanche activity, a widespread cycle to size 2.5 occurred in the mountains west of Kimberley. 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
15 - 25cm of light density snow has fallen over the last few days. This snow is settling nicely and likely being formed into soft wind slabs immediately lee of ridge crest.Numerous crust can be found in the upper 30 cm of the snowpack on south facing slopes. These crusts produce sudden collapse failures in snowpack tests. A moderate shear persists down 30 - 50cm on the March 15 crust/surface hoar interface. Down 70 - 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. It also continues to produce sudden planar failures in compression tests.The deeper facet/crust persistent weakness buried at the beginning of February, now down 100 - 180cm, seams to be more active in this region than any other in the province and is still very difficult to trust. Needless to say, any avalanche at these deeper, persistent interfaces would be large and destructive. It continues to produce large destructive natural avalanches every few days.Weak basal facets exist in many areas, but without a large load, triggering now is unlikely.
Problems
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.
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.
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.