Avalanche Forecast
Issued: Feb 25th, 2022 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
jleblanc,
Avalanche Canada
Rider-triggered avalanches remain possible. Identify features of concerns for wind slabs and persistent slabs by reading the Avalanche Problems section.
Summary
Confidence
Weather Forecast
A strong ridge of high pressure will keep the region dry and cold, with the potential for lingering valley clouds. The next round of snow is expected late Sunday night as a shift in the weather pattern will occur.
Friday night: Clear skies. Lingering valley clouds. Alpine temperatures around -15 C. Light northwesterly winds.
Saturday: Increasing cloudiness. Freezing level rising to 800 m. Alpine temperatures around -8 C. Light to moderate southwesterly winds.
Sunday: Snow 5-10 cm. Freezing level rising to 1100 m. Alpine temperatures around -4 C. Moderate to strong southwesterly winds.
Monday: Snow 15-20 cm. Freezing level rising to 1400 m. Alpine temperatures around -2 C. Moderate to strong southwesterly winds.
Avalanche Summary
Wind slabs are still showing signs of instability on isolated features as human-triggered and natural avalanches have been reported thought out the region. A large avalanche (size 2) caught a skier by surprise on a steep lee slope, reloaded by the wind in the Selkirks. The failure plane was identified as a buried surface hoar layer from mid-February. Continued snow transport triggered a cornice fall which produced a very large slab avalanche (size 3) near London Ridge.
Persistent slabs were also observed lately, such as two very large avalanches (size 3) reported near London Ridge and in the Valhallas. They both occurred naturally on south-westerly alpine slopes. This evidence is showing that, with added load to the snowpack from the last weekend’s storm and continued winds, the mid-January weak layer began to "wake up".
Snowpack Summary
Recent cold temperatures and northerly winds have modified and transported the last storm snow (20-80 cm), creating heavily wind-affected surfaces in exposed areas and wind slabs in lee areas. Below ~1200 m, 10-20 cm of snow is now overlying a thick melt-freeze crust.
Up to 80 cm is burying a weak layer formed in mid-February. This layer consists of surface hoar in sheltered areas, a melt-freeze crust at lower elevations, a sun-crust on steep solar aspects, and hard wind-affected snow in the alpine and exposed treeline. Reports suggest that in many areas, the recent snow is bonding poorly to this firm layer.
The mid-January surface hoar/crust layer is now down 50-150 cm in the snowpack. This layer has started to 'wake up' following last weekend's snowfall.
Terrain and Travel
- Recent wind has varied in direction so watch for wind slabs on all aspects.
- Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
- Shooting cracks, whumphs and recent avalanches are strong indicators of an unstable snowpack.
- Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
Problems
Wind Slabs
Wind slabs exist on various aspects in any exposed terrain and around ridgelines. Shifting winds (initially from the southwest, then switching to the northeast) have built slabs in less common locations. These slabs may have formed on top of old crusts and hard wind-pressed snow. Uncertainty remains about how well they will bond to old surfaces due to continued cold temperatures.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
There are two prominent weak layers in the upper meter of the snowpack.
An upper layer exists down ~30-70 cm and is comprised of surface hoar in sheltered areas, a crust at lower elevations and on solar aspects, and hard wind-affected snow in the alpine and exposed treeline. Reports suggest that reactivity on this layer may persist. Be particularly cautious in sheltered areas where surface hoar may be preserved, or south-facing aspects where recent wind-loading has occurred, and a sun crust may be buried.
The lower layer may be found roughly a meter deep in the snowpack. This layer consists of faceted snow, a sun crust on steep solar aspect, and most notably large surface hoar crystals in sheltered terrain. The last storm caused this layer to 'wake up' on northerly aspects around treeline. The most reactivity on this layer has been seen between 1600-2200 m in open areas in the trees, in cut blocks, and on steep convexities. Terrain features to be suspect of include the lee side of ridges, openings in trees, cut blocks, and burns, especially on northerly aspects where the layer may not be capped by a firm crust.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Feb 26th, 2022 4:00PM
