Avalanche Forecast
Issued: Feb 24th, 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
Yellow means caution ! Wind slabs are still reactive to human triggering on all aspects, and buried surface hoar layers remain suspicious on open slopes. Make sure to read the section Avalanche Problems.
Summary
Confidence
High - Confidence is due to a stable weather pattern with little change expected.
Weather Forecast
The ridge of high pressure will keep the region dry and cold, with the potential for lingering valley cloud and an alpine temperature inversion on Friday and Saturday. The next storm is expected for the weekend as a shift in the weather pattern will occur.
Thursday night: Clear skies. Patchy valley cloud. Alpine temperatures around -20 C. Moderate to strong northwesterly winds.
Friday: Mix of sun and clouds. Lingering valley cloud. Alpine temperatures around -12 C. Light to moderate northwesterly winds.
Saturday: Cloudy with light snowfall. Freezing level rising to 1000 m. Alpine temperatures around -8C. Strong southerly winds.
Sunday: Snow 5-10 cm. Freezing level rising to 1200 m. Alpine temperatures around -6 C. Strong to extreme southerly winds.
Avalanche Summary
On Wednesday, a storm slab avalanche was accidentally human-triggered on a short, steep treeline slope that was previously skied.Â
Earlier this week, shifting arctic winds have redistributed the storm snow into wind slabs and several natural avalanches occurred. Evidence of a widespread natural avalanche cycle from the last weekend’s storm is still visible.
As the last storm added load to the snowpack, the mid-January weak layer began to "wake up". In the neighboring region of North Colombia, large cornice-triggered natural persistent slab avalanches on an east aspect at treeline were reported.Â
Snowpack Summary
Last weekend's storm brought 20-80 cm of new snow accompanied by southwesterly winds. Recent northeasterly has created a heavily wind-affected surface in exposed areas and redistributed storm snow into wind slabs in lee areas. Below ~1200 m the majority of the precipitation fell as rain, with 10-20 cm of snow now overlying a thick melt-freeze crust.Â
Up to 120 cm now overlies a weak layer formed in mid-February. This layer is comprised 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 storm snow is bonding poorly to this firm layer.
The late-January surface hoar/crust layer is now down 50-150 cm in the snowpack. During last weekend's snowfall, there was reactivity on this layer in the neighbouring Colombia regions. This layer may also be a concern in the Cariboos with a similar upper snowpack composition.
Terrain and Travel
- Recent wind has varied in direction so watch for wind slabs on all aspects.
- Closely monitor how the new snow is bonding to the old surface.
- Shooting cracks, whumphs and recent avalanches are strong indicators of an unstable snowpack.
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) are building slabs in less common locations. These slabs may have formed on top of old crusts and hard wind-pressed snow, and there is uncertainty about how quickly they will bond to old surfaces.
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 ~50-100 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 storm snow is bonding poorly to this hard interface in many areas, and 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 100-150 cm 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. Over the past few weeks, reactivity on this layer had tapered, but the storm over the weekend 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, cut blocks, and 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: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Feb 25th, 2022 4:00PM
