Bollettino valanghe

Lizard-Flathead

Feb 10 – 11, 2021Avalanche Canada
Vedi sulla mappa
Archiviato · scaduto 6 years ago

Pericolo valanghe

Fri
Sat
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
Apri la mappa completa

In sintesi

Obvious clues like shooting cracks, whumpfing, and avalanches are decreasing but a persistent weak layer lurks in the snowpack! A conservative mindset is best applied when dealing with a persistent problem and extreme cold.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2.5

    40-65 cm snow sits above a buried weak layer of surface hoar, facets, and a crust. Recently, slabs have been very reactive to human triggers, surprising riders, and showing wide propagations in moderate to low angle terrain. This widespread layer has shown more reactivity on northerly aspects, however prominent surface hoar continues to be reported in test profiles on all aspects. Moving forward, cold temperatures may decrease the cohesive nature of the slab, but any input of wind or precipitation could easily re-ignite this weak layer. Heads up, we're moving into a low probability-high consequence scenario.

Confidence

High - Uncertainty is due to the fact that deep persistent slabs are particularly difficult to forecast. Confidence is due to a stable weather pattern with little change expected.

Weather Forecast

TUESDAY NIGHT - Cold and cloudy / light north wind / alpine low temperature near -30

WEDNESDAY - Cold, partly cloudy and isolated flurries / light northeast wind / alpine high temperature near -26

THURSDAY - Cold and mostly sunny / moderate and increasing northeast wind / alpine high temperature near -26

FRIDAY - Cold and sunny / moderate northeast wind / alpine high temperature near -20

Avalanche Summary

On Monday, skiers accidentally triggered 2 small (size 1) avalanches down 45 cm, likely on surface hoar.

On Sunday a cornice failure triggered a small (size 1) avalanche with a 50 cm crown. Skiers reported sudden results in test profiles on prominent surface hoar on a variety of aspects buried 50 cm deep.

Last week was busy for avalanche activity, on Wednesday (Feb 3) persistent slab avalanche activity really picked up with reports of natural, human, and explosives triggered storm and/or persistent slab avalanches up to size 2 everyday through Saturday (Feb 6). 

On Saturday (Feb 6) riders continued to trigger slab avalanches 20-60 cm deep, documented in a handful of MIN reports (Trespass, Mammoth, Spicy, Different Day). Explosives triggered several large (2-2.5) persistent slab avalanches on northerly aspects below 2000 m.

On Friday (Feb 5), there were numerous reports of natural and human triggered persistent slab avalanches up to size 2.5. Some of these were triggered remotely, as outlined in a MIN report that can be viewed here. There were also numerous natural and explosives triggered dry loose, and storm slab avalanches reported up to size 2. 

Many thanks for all of the great MIN reports over the past week!

Snowpack Summary

Surface faceting and surface hoar growth is occurring with clear nights and frigid temperatures. Recent northerly and shifting winds have reverse loaded features, slabs may be found in lee terrain on a variety of aspects. 

A persistent weak layer lurks 30-70 cm below the surface, consisting of surface hoar, facets, and a crust buried in late January. This layer has been responsible for the majority of recent avalanche reports and has been easily found on all aspects, reports suggest it is touchiest on northerly and easterly aspects. It's likely that reactivity will decrease with the cold and calm weather, however any inputs (like wind or snow) encouraging a slab to form could quickly make this layer reactive.

Below 1600 m a hard melt-freeze crust is underneath 20-40 cm recent snow. 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

  • Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
  • Avoid terrain traps such as gullies and cliffs where the consequence of any avalanche could be serious.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Be aware of highly variable recent wind loading patterns.

Regioni coperte