Regions
Vancouver Island.
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Saturday: Numerous new slab avalanches reported thought the storm period, up to size 1.5 mostly north aspects, between 1800 and 1200 meters.
Sunday: No new avalanches have been observed or reported.
Past Weather
Past precipitation amounts where highly variable over the forecast areas with up to 30 centimeters in the southern zones and the north western zone receiving 15cms.Beginning Sunday, a trough of low pressure associated with a weak front will approached the region bring to the forecast area, rising temps and freezing levels. Initially precipitation was in the form of snow, but slowly transitioned to rain at elevations below 500 meters.
Weather Forecast
A frontal system will enter the region Monday will deliver over a 48 hour period precipitation combined with rising freezing levels and temperatures . Expect on Wednesday clearing sky and cooling temperatures.Monday: 15 to 30 cm , Winds Light to Moderate from the South East, Freezing levels at 500 to 800 meters.Tuesday: 5-10 cm, Winds Light to Moderate from the North West, Freezing levels 600 to 1000 meters.Wednesday: No new precipitation Winds Moderate from the South East, switching to North West, Freezing level from sea level rising to a daytime a high of 400 meters.
Terrain Advice
Dangerous avalanche conditions exist. Careful snowpack evaluation, cautious route-finding and conservative decision-making is essentialAvoid convex roll features.Seek terrain that is well supported.Caution when transitioning from areas scoured by the wind into areas with recent wind loading.
Snowpack Summary
Past wind slabs predominantly on South aspects are now buried and will continue to be buried with the current storm snow. New snow has buried surface hoar from size 10 to 20mm found at Tree line and below in specific areas protected from the wind and sun. During travel take the time to observe where this fragile layer is and its sensitivity to testing. Many areas prior to this past storm had time to both facet and become smooth and hard over the extended period of cool , clear and windy conditions, expect this new snow to take time to bond to these surfaces and expect the new storm slab to remain unstable and easy to trigger from light loads. The Jan 23, 2021 Persistent weak layer can be found between 60 and 100 cm deep and over the past forecast period, was reactive to testing.
Snowpack Details
- Surface: New snow overlies and variety of surfaces including surface hoar and faceted smooth surfaces.
- Upper: Facet and low density snow overlies a dense and strong layer of well bonded and settled snow.
- Mid: An eroding crust with facets at its base ( JAN 21 PWL).
- Lower: Well settled.
Confidence
Moderate - Numerous observations and reports from a wide variety of the zones within the forecast area. Excellent field data and good agreement between weather models.
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.
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.