Bollettino valanghe

South Columbia

Feb 12 – 13, 2022Avalanche Canada
Vedi sulla mappa
Archiviato · scaduto 5 years ago

Pericolo valanghe

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

In sintesi

A dangerous dilemma exists in sheltered, shaded areas where dry powder may be preserved, but a lethal layer of surface hoar could remain ripe for human triggering.

These beautiful warm sunny days are best enjoyed in low angled alpine terrain with no exposure to overhead hazard.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Strong westerly winds throughout the week have created wind slabs in the alpine. Wind slabs may be stubborn to human triggering but have the potential to step down to buried weak layers, creating large avalanches.

    Cornices may become weak with warm temperatures. Cornice failures put a large load on the snowpack, and have the potential to trigger buried weak layers, resulting in large destructive avalanches. 

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1.5–3

    A weak layer formed by clear skies and warm temperatures in late January may be found 40 to 80 cm deep in the snowpack. This layer consists of facetted snow, a sun crust on steep solar aspect, and most notably large surface hoar crystals in sheltered terrain.

    This layer has been the culprit of several large human-triggered avalanches in the past week and remains a concern, especially as the snowpack is being tested with warm temperatures and strong solar radiation. 

    The problematic surface hoar layer will be most prominent in sheltered areas at treeline and below. Terrain features to be particularly cautious around include the lee side of ridges, openings in trees, cut blocks, and burns. Triggering this layer from a distance away is a concern, watch out for adjacent and overhead slopes.

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Warm temperatures compounded by strong solar radiation may create wet loose avalanches on steep solar aspects in the afternoon. 

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast. Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

A ridge of high pressure continues to bring clear skies and dry conditions into Saturday. 

Friday Overnight: Clear. Freezing level dropping to valley bottom. Light ridgetop winds. 

Saturday: Mainly clear, some valley cloud may develop. Freezing level rising to 1300 m with an alpine temperature inversion. Light northwest winds at ridgetop.

Sunday: Cloud cover increasing. Freezing level rising to 1000m. Light westerly winds at ridgetop.

Monday: Snowing. Freezing level rising to 1000 m in the afternoon. Light to moderate westerly winds at ridgetop.

Avalanche Summary

A persistent weak layer of buried surface hoar continues to be reactive to human triggered producing numerous large avalanches in the past week, surprising both professionals and recreationists. This layer has shown the most reactivity between 1600-2200 m in open areas in the trees, in cut blocks and on steep convexities. Compelling observations on this layer from the neighbouring region of Glacier National Park can be seen here. 

Snowpack Summary

Overnight, clear skies and cooling temperatures will refreeze the surface of the snowpack. A thin breakable crust exists on all aspects and elevations, while a thicker more prominent crust can be expected at lower elevations and on south-facing aspects. Warm daytime temperatures and strong solar radiation will likely cause these crusts to break down throughout the day.

Strong westerly winds throughout the week have created extensive wind-effect in open areas at all elevations. Expect to find old and new wind slabs on a variety of aspects, with the most recent and reactive slabs formed in terrain features lee to the northwest. 

Several weak layers exist in the upper snowpack including buried crusts, facets, and a prominent weak layer of surface hoar. This surface hoar is the dominating feature. It was buried in late January and exists 40 to 80 cm deep in the snowpack. Reports suggest that the surface hoar is most prominent in sheltered openings at and below treeline.

The facet/crust layer that formed in early December is buried around 100 to 240 cm. The last reported avalanche was on February 7 in the southwest of the region. Although unlikely, the layer could be triggered from a large load like a cornice fall or a shallower slab avalanche could step down to this layer. Humans are unlikely to trigger it, with perhaps the exception in thin, shallow snowpack areas. Check out the forecaster blog for more information.

Terrain and Travel

  • Uncertainty is best managed through conservative terrain choices at this time.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • Surface hoar distribution is highly variable. Avoid generalizing your observations.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Avoid exposure to steep, sun exposed slopes, especially when the solar radiation is strong.

Regioni coperte