Avalanche Forecast
Issued: Feb 23rd, 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.
zryan,
Avalanche Canada
Wind slabs have been reactive to human triggers in recent days. As you enter wind-affected terrain, watch for wind slabs on all aspects.
The presence of a persistent slab problem warrants caution on open slopes and convex rolls at treeline where buried surface hoar may exist.
Summary
Confidence
Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.
Weather Forecast
The ridge of high pressure will rebuild on Thursday, with the potential for lingering valley cloud and an alpine temperature inversion on Friday and Saturday.Â
Wednesday Overnight: Light snowfall. Alpine temperatures around -15 C. Light to moderate northwesterly winds.
Thursday: Clearing, patchy valley cloud. Alpine temperatures around -15 C. Light northerly winds.
Friday: Mainly clear, lingering valley cloud. Freezing level rising to 500 m. Alpine temperatures around -12 C. Light to moderate northwesterly winds.
Saturday: Increasing cloud cover. Freezing level rising to 800 m. Alpine temperatures around -6 C. Moderate to strong northwesterly winds.
Avalanche Summary
During the peak of the storm on Saturday, numerous natural and human-triggered storm slabs were reported on all aspects due to rapid loading. Larger natural and human-triggered wind slab avalanches were reported in wind-loaded terrain in the alpine and treeline. Several natural dry loose avalanches were reported out of steep terrain on all aspects.
As this storm added load to the snowpack, the mid-January weak layer began to "wake up". Operators reported a large cornice-triggered natural persistent slab avalanche on an east aspect at treeline. In the neighbouring South Colombia, two human-triggered avalanches occurred on northerly aspects at or just above treeline.
As arctic air invaded the province on Monday and Tuesday, strong northerly winds redistributed the storm snow into wind slabs on southerly aspects. A natural avalanche cycle occurred on southerly aspects as a result of this wind-loading. Several human-trigged wind and storm slab avalanches were also reported on these days.Â
Snowpack Summary
Last weekend's storm brought 30-100 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 mid-January surface hoar/crust layer is now down 50-150 cm in the snowpack. There has been reactivity on this layer during last weekend's snowfall. See the avalanche summary for more details.
The facet/crust layer that formed in early December is now buried around 150 to 250 cm. This layer is currently considered dormant but could become active later this season.Â
Terrain and Travel
- Recent wind has varied in direction so watch for wind slabs on all aspects.
- Keep your guard up at lower elevations. Wind slab formation has been extensive.
- 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.
- Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
Problems
Wind Slabs
Wind slabs will exist on various aspects in exposed terrain and around ridgelines. Last weekend's storm initially came in with southwest winds, but with the intrusion of arctic air, winds switched to the northeast, 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: All elevations.
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, 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 24th, 2022 4:00PM
