Bollettino valanghe

Lizard-Flathead

Dec 27 – 28, 2020Avalanche Canada
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Archiviato · scaduto 6 years ago

Pericolo valanghe

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

In sintesi

Recent winds have created windslabs in exposed treeline & alpine regions. If triggered these could step-down to deeper layers causing large avalanches. Enjoy the holiday riding & be sure to make continued conservation decisions that avoid steep avalanche terrain in the alpine. 

Problemi valanghivi

  • Wind Slabs

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

    Natural avalanche activity continues to taper with the end of the snowfall and easing of winds. However, recent moderate to strong west/southwest winds have created fresh windslabs on lee north and east slopes and cross-loaded features making the snowpack primed for human triggering. Be on the look-out for cornice formation: these are a hazard underfoot as well as being an overhead hazard that is capable of triggering large avalanches should they fail.

    Loose-dry sluffing from sheltered steep terrain is likely, especially when the sun comes out or when transitioning into steeper terrain.

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely - Possible
    Dimensione
    1.5–3

    This layer reached a tipping point with recent new snow as evidenced by the recent natural avalanche cycle. Although naturally triggered avalanches have tapered, it remains possible to tigger this layer in thin to fat zones, with a step-down avalanche or on slopes that have received significant wind transport. Depending on elevation and aspect, 60-150 cm of snow currently sits above buried weak layers from early December. Sugary, facets and surface hoar around the crust mean persistent slabs remain reactive, especially with large triggers or in a shallow snowpack. This layer appears to be more concerning above 1700m and on northerly aspects.

Confidence

Moderate - Uncertainty is due to the limited number of field observations. Confidence is due to a stable weather pattern; little change is expected for several days.

Weather Forecast

A weak weather system will bring light snow, moderate west/southwest winds and cool temps for the weekend ahead of a building high pressure system for Monday / Tuesday.

Saturday night: Cloudy with clear periods and isolated flurries. Alpine low temperatures near -9C and freezing levels valley bottom. Ridgetop wind light to moderate from the west / northwest.

Sunday: A mix of sun and clouds with isolated flurries. Alpine high temperatures near -8C and freezing levels valley bottom. Ridgetop wind light and variable gusting moderate.

Monday: Mix of sun and cloud. Alpine high temperatures near -9C and freezing levels valley bottom. Ridgetop wind light and variable west.

Tuesday: Mix of sun and cloud. Alpine high temperatures near -12 and freezing levels valley bottom. Ridgetop wind light and variable.

Avalanche Summary

From Saturday there were reports of several intentionally triggered small (size 1) soft wind slab avalanches and a small (size 1) explosive triggered avalanche from a cross-loaded alpine feature at treeline. Sluffing of loose dry snow is building mass to size 1 from steep wind sheltered terrain. A nearby neighbour reported a large avalanche (size 2) that imitated as a windslab or cornice failure and stepped down to the December crust on Friday. Another neighbour reported a large (size 2) windslab from a west aspect from cross-loading from recent variable east winds.  

On Thursday there were reports of small (size 1) and large (size 2) windslabs from explosive control within the region and explosive controlled very large (size 3) avalanches and cornice triggered very large (size 2.5-3) avalanches from adjacent regions.  

During the height of the cycle on Wednesday there were numerous storm slabs up to size 1.5 that were triggered with explosives. This MIN from Tunnel creek on Dec 24th also reports numerous large avalanches on cross loaded features at treeline. On Tuesday, a widespread natural avalanche cycle up to size 3 was reported from the lizard range with many avalanches reported from northerly aspects. 

Please consider sharing your observations on the Mountain Information Network. Thank you to those that have already submitted this winter!

Snowpack Summary

30-60 cm of recent snow blanketed the region by Tuesday morning and has been blown by moderate to strong winds in exposed treeline and above since then. Moderate to strong west and southwestern winds created significant ridgetop snow re-distribution onto lee slopes. Wind slabs will likely remain reactive to human triggers, and are the most reactive during periods of moderate to strong winds. Cornice development may be found along ridgecrests and deep windslabs on lee slopes. 

Recent snow fell on a variety of old surfaces including a buried melt-freeze crust reported below 1700m and surface hoar reported around treeline. This Min from Mt. Fernie on Dec 26th found 5-15cm of low density snow above this recent crust while this Min near Tunnel Creek found it down 20cm.  

Buried 60-130cm one can find a variety of weak layers from early December. This persistent weak layer, with facetted crystals and surface hoar crystals above and/or below it is reaching a tipping point. Deeper in the snowpack are two hard melt-freeze crusts that formed in November that may have some weak crystals around them. This potential avalanche problem is dormant at this time, however; it remains on our radar.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Approach lee and cross-loaded slopes with caution.
  • Shooting cracks, whumphs and recent avalanches are strong indicators of an unstable snowpack.
  • Minimize your exposure time below cornices.
  • Don't let the desire for deep powder pull you into high consequence terrain.

Regioni coperte