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Avalanche Forecast

Archived

Jan 18th, 2022–Jan 19th, 2022

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

Regions

Purcells.

Variable conditions exist throughout the region, with increased recent snow amounts in the north. Keep your guard up as isolated pockets of wind slabs are still showing signs of reactivity. 

Confidence

Moderate - Uncertainty is due to field data and reports showing a wide variation in conditions throughout the region.

Weather Forecast

TUESDAY NIGHT: Partly cloudy, light northwest wind, treeline temperatures around -6 C, freezing level lowering to valley bottom.

WEDNESDAY: Sunny periods, light north wind, treeline temperatures around -10 C, freezing level at valley bottom.

THURSDAY: Snow up to 5 cm, moderate-strong southwest wind, treeline temperatures around -6 C, freezing level rising to 1000 m.

FRIDAY: Sunny periods, light southwest wind, treeline temperatures around -6 C, freezing level rising to 1000 m.

Avalanche Summary

Reactive wind slabs have caught riders by surprise recently, with large (size 2) avalanches releasing on alpine lee features and open areas at treeline.

Over the last week, the early December persistent weak layer has produced few large natural avalanches (2-2.5) in the center of the region. Explosive controls have also produced few size 2 avalanches that failed on the same persistent weak layer, one being remotely triggered. These occurred on thin to thick features on northeast-facing slopes from between 1600 m and 2000 m, where the layer was buried 100 cm + deep. Although avalanche activity has tapper off, it remains a concern across the region.

Snowpack Summary

In the last two days, fresh snow has been redistributed on alpine lee slopes and open areas at treeline. Around 1900 m and below, a crust is now capping the dense 10-30 cm of snow which has settled significantly with the past mild temperatures. The crust varies from thin/breakable to thick/supportive, according to the aspects and elevation. Below the recent snow, a layer of feathery surface hoar and melt-freeze crusts are found, which seems to be still reactive in isolated pockets areas. Lower elevations have gone through a melt-freeze cycle with past elevated freezing level with elevated freezing levels.

The most notable layer of concern in the snowpack is a crust that was formed in early December and is now down 90-160 cm. Activity on this layer has been sporadic but has generally been triggered on steep, rocky slopes, with a shallow or thin-to-thick snowpack.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.