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Avalanche Forecast

Archived

Feb 22nd, 2022–Feb 23rd, 2022

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Cariboos.

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.

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. 

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.

 

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. 

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. 

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 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.

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.