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Avalanche Forecast

Archived

Feb 16th, 2021–Feb 17th, 2021

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

Lizard-Flathead.

Conservative decision-making is still essential! Slabs on the late January persistent weak layer consisting of surface hoar and sugary facets continue to be reactive to skiers and riders. Don't let your guard down while this layer takes its time to heal.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

TUESDAY NIGHT: Mostly cloudy, trace to 5 cm new snow, light westerly wind, temperature low -15 C.

WEDNESDAY: Mix of sun and cloud, trace of new snow, light northwest wind, temperature high -7 C.

THURSDAY: Mix of sun and cloud, trace of new snow, light westerly wind, temperature high -8 C.

FRIDAY: Mostly cloudy, up to 5 cm new snow, light southwest wind, temperature high -7 C.

Avalanche Summary

On Monday, skiers triggered size 1 avalanches at treeline and in the alpine on northeast aspects. One avalanche was triggered from a short distance away (see this MIN report). On Sunday skiers triggered avalanches up to size 2.5 on open features at the treeline/alpine interface in the Lizard Range and Tunnel Creek. These failed on the late January persistent surface hoar layer (see this MIN as an example). 

On Thursday and Friday there were human and remote triggered avalanches up to size 2 reported. Locations like Mount Fernie, 2000, Liverwurst and McDermid were a few location examples. Some avalanches were triggered from a distance away. 

Snowpack Summary

Surface faceting and surface hoar growth is promoted by clear nights and frigid temperatures. Below 1600 m a hard melt-freeze crust is underneath 20-40 cm recent snow. 

A persistent weak layer lurks 30-70 cm below the surface. In some places it consists of surface hoar, in other places just facets, or crust/facet combinations. This weak interface has been responsible for the majority of recent avalanches. Reports suggest the surface hoar interface at treeline is the biggest repeat offender, and things have been most reactive on northerly and easterly aspects, but don't let your guard down elsewhere.

A solid mid-pack sits above a deeply buried crust and facet layers near the bottom of the snowpack (150-200 cm deep), which is currently unreactive. 

Terrain and Travel

  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Avoid terrain traps such as gullies and cliffs where the consequence of any avalanche could be serious.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.

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.