Avalanche Forecast
Issued: Feb 22nd, 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
Recent storm snow may bond poorly to the underlying surface. Reactivity on this weak layer could persist, particularly in wind-loaded terrain.
Reverse loading from strong northeast winds has built wind slabs on unusual aspects, which could take riders by surprise.
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
A weak disturbance will come through on Wednesday with a light amount of snowfall expected in the region. The ridge of high pressure will reestablish on Thursday.Â
Tuesday Overnight: Increasing cloud cover. Winds shifting northwest and increasing moderate to strong. Alpine temperatures rising to around -15 C.
Wednesday: Mainly cloudy, light snowfall. Light to moderate westerly winds. Alpine temperatures rising to -15 C.
Thursday: Partially cloudy. Light to moderate northwesterly winds. Alpine temperatures around -15 C.
Friday: Partially cloudy. Moderate to strong northwesterly winds. Alpine temperatures around -10 C.
Avalanche Summary
Observations were limited during the peak of the storm on Saturday evening, but operators suspect a widespread natural avalanche cycle occurred. In the neighboring North Colombia, numerous human-triggered storm slabs and wind slabs were reported at all elevations, with many of these avalanches failing on the mid-February drought layer.
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As artic air invaded the province on Monday, strong northerly winds redistributed the storm snow into wind slabs on southerly aspects. A few natural avalanches occurred on southerly aspects as a result of this wind-loading.
As this storm added load to the snowpack, the mid-January weak layer began to "wake up". In the North Colombia, operators reported a large cornice-triggered natural persistent slab avalanche on an east aspect at treeline. In the South Colombia, two human triggered avalanche occurred on northerly aspects at or just above treeline.
Snowpack Summary
Last weekend's storm brought 20-80 cm of new snow accompanied by southwesterly winds. 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. 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. See the avalanche summary for more details.
The facet/crust layer that formed in early December is now buried around 150 to 250 cm. Human triggering of this layer is unlikely, except perhaps on a re-loaded bed surface or in a shallow snowpack area. This layer may become a concern during periods of warming or heavy loading.Â
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.
- Use small low consequence slopes to test the bond of the new snow.
- Shooting cracks, whumphs and recent avalanches are strong indicators of an unstable snowpack.
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 roughly 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: All elevations.
Likelihood
Expected Size
Valid until: Feb 23rd, 2022 4:00PM
