Bollettino valanghe

South Rockies

Feb 20 – 21, 2021Avalanche Canada
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Archiviato · scaduto 6 years ago

Pericolo valanghe

Mon
Tue
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
Apri la mappa completa

In sintesi

Strong westerly wind might have formed reactive wind slabs in the southeast of the region. Persistent slabs continue to be easily triggered by skiers and riders. In the Elk Valley the Lizard-Flathead forecast with danger rating Considerable at treeline is more appropriate.

Problemi valanghivi

  • Wind Slabs

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

    Strong westerly wind in the southeast of the region might have formed reactive wind slabs in lee terrain features in the alpine and open areas at treeline on Friday. Moderate west wind will continue to form wind slabs throughout the day. Look out for wind slabs in unusual places. Recently localized moderate to strong winds blew from variable directions. 

    Wind slabs are slow to bond where they sit over cold sugary facets. There is also potential for wind slabs to step down to the late January persistent weak layer. 

  • Persistent Slabs

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

    This layer continues to be easily triggered by skiers and riders. 40-65 cm of snow sits above a buried weak layer of surface hoar, facets, and a crust (depending on elevation and aspect). Reports suggest the persistent weak layer at treeline in the Elk Valley is the biggest repeat offender, and things have been most reactive on northerly and easterly aspects, but don't let your guard down elsewhere. 

    Small terrain features are producing small avalanche results, bigger features can produce larger more dangerous avalanches. These kinds of avalanches can happen in surprisingly mellow terrain and be triggered from a distance away.

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

FRIDAY NIGHT: Cloudy with clear periods, moderate west wind, temperature low -13 C.

SATURDAY: Mostly cloudy, trace of new snow, moderate west wind, temperature high -7 C.

SUNDAY: Mostly cloudy, 5 cm new snow, strong to extreme southwest wind, temperature high -2 C, freezing level rising to 1700 m. 

MONDAY: Cloudy, 10 cm new snow and rain at lower elevations, strong to extreme southwest wind, temperature high +1 C, freezing level at 1900 m.

Avalanche Summary

Several explosives triggered slab avalanches up to size 2 and several natural and skier triggered dry loose and wind slab avalanches up to size 1.5 were reported on Thursday. 

On Tuesday and Wednesday a few wind slab avalanches up to size 2 were triggered by explosives and released naturally. 

Several wind slab avalanches up to size 2 were triggered by skiers and released naturally at treeline and in the alpine on Monday. Human triggered avalanches were reported north of Crowsnest Pass. The avalanches were triggered on east aspects on mellow slopes in the alpine and at the treeline/alpine interface (see this MIN report). The failure plane of these avalanches is likely the late January persistent weak layer consisting of surface hoar, sugary facets or a crust/facet combination. 

Snowpack Summary

5-15 cm recent snow sit on top of wind affected snow surfaces in the alpine and open areas at treeline and a facet layer which is up to 20-30 cm thick in sheltered areas. A persistent weak layer lurks 40-65 cm below the surface. In some places it consists of surface hoar, in other places just facets, or crust/facet combinations. 

A solid mid-pack sits above deeply buried decomposing crust and facet layers near the bottom of the snowpack. Though unreactive under the current conditions, steep rocky slopes and shallow snowpacks should still be approached with caution.

Terrain and Travel

  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • 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.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.

Regioni coperte