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Avalanche Forecast

Archived

Mar 14th, 2022–Mar 15th, 2022

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

Regions

North Rockies.

Conservative terrain selection will be critical as riders have been surprised in recent days by large avalanches failing on a weak layer of surface hoar. 

Choose low consequence features and watch for signs of instability like whumpfing, shooting cracks or recent avalanches.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast. Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

A series of frontal systems impacting the coast will bring continued snowfall throughout the week.

Monday Overnight: Overcast to obscured skies. Rain at lower elevations and snowfall above ~1500 m, trace to 10 cm of accumulation, heaviest in the Kakwa. Moderate to strong southwest winds at ridge top. Freezing level around 1700 m.

Tuesday: Mainly cloudy with continued precipitation, trace to 10 cm of new snow accumulation at higher elevations. Moderate to strong southwest winds. Freezing level around 1500 m.

Wednesday: Mix of sun and cloud with light flurries. Moderate to strong westerly winds. Freezing level around 1500 m.

Thursday: Mainly cloudy with light precipitation, 1-5 cm of new snow accumulation at higher elevations. Moderate to strong westerly winds. Freezing level around 1600 m.

Avalanche Summary

Numerous natural and sledder-triggered avalanches were reported throughout the weekend in the Pine Pass area down 25-70 cm, all failing on surface hoar. The most reactivity occurring on wind-loaded, north-east aspects. Most notably, a size 2.5 sledder-triggered avalanche occurred near Bijoux Falls. The full report can be seen here.

A few sledder-triggered avalanches up to size 2 were reported in the Renshaw area on Sunday. These storm slabs were failing on a weak layer of surface hoar down 25-40 cm.

Snowpack Summary

Last weekend's 15-30 cm of new snow and moderate southwest winds formed wind slabs in areas exposed to southwest winds in the alpine and treeline. 

This new snow is sitting on various surfaces, including hard wind-affected snow, sun crusts on southerly slopes, and most notably large surface hoar on shady or sheltered slopes. This layer of surface hoar is expected to remain problematic in the coming days, with the most reactivity observed in the Pine Pass and Renshaw area.

The mid and lower snowpack is generally well-settled and strong in most areas, with multiple crusts throughout. No recent persistent slab avalanches have been reported on these layers.

Terrain and Travel

  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Back off slopes as the surface becomes moist or wet with rising temperatures.

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.