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Avalanche Forecast

Archived

Feb 3rd, 2022–Feb 4th, 2022

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

Regions

Purcells.

Wind slabs will continue to form at higher elevations.

Approach steep open slopes at treeline and below with caution. A buried surface hoar layer may be reactive and can produce larger avalanches than you expect. Watch for signs of instability as you travel. 

Confidence

Moderate - We are confident about the possible sizes of avalanches, should one release; what is less certain is the likelihood of triggering.

Weather Forecast

Light snowfall is forecast for Friday. Temperatures rise and skies clear for the weekend.

THURSDAY NIGHT: A mix of sun and clear breaks, moderate westerly winds. Freezing level at valley bottom. Isolated flurries. 

FRIDAY: Mostly cloudy, with up to 5 cm expected, favouring the north. Strong westerly winds. Freezing level around 500 m. Alpine high of -6. 

SATURDAY: Another 5cm by Saturday morning is possible, with strong westerly winds. A mix of sun and cloud. Freezing level rises towards 1200 m. High of -5. 

SUNDAY: Mostly clear with strong westerly winds. Freezing level rises towards 1900 m, with a high of 0.

Avalanche Summary

On Wednesday, riders triggered slabs to size 1. Remote triggers were also reported, producing small slab avalanches failing on the buried surface hoar layer. Small natural wind slabs were also observed in steep terrain features. 

Natural wind slabs have been observed throughout the week, during peak loading from strong westerly winds. Loose dry avalanches have also been reported, from steep terrain features.

Snowpack Summary

At lower elevations, 20-40 cm of storm snow sits over a melt freeze crust. In sheltered terrain a widespread layer of large surface hoar crystals sits immediately above the crust, which may be sensitive to human triggers. 

At higher elevations the storm snow has been redistributed into pockets of wind slab by strong westerly winds. A thin melt freeze crust extends into the alpine on solar aspects. This crust may sit on the surface in exposed terrain, or below wind deposited snow in sheltered features increasing reactivity.

Several surface hoar layers are now buried in the upper snowpack 30-60cm deep. The early December crust/facet layer of concern sits around 80 cm deep in the eastern Purcells and shallow terrain, and up to 150 cm in the west. This layer produced numerous large avalanches in January, and is now considered dormant. We will continue to track this layer of concern and expect it will wake up again with major warming or a large storm event. This recent forecaster blog goes into more details on the layer and how to manage it. 

Terrain and Travel

  • Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.
  • Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
  • Be alert to conditions that change with elevation and wind exposure.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.

Problems

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.

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.