Bollettino valanghe

Yukon

Dec 14 – 15, 2021Avalanche Canada
Vedi sulla mappa
Archiviato · scaduto 5 years ago

Pericolo valanghe

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

In sintesi

The north wind has formed widespread wind slabs, even in low elevation terrain. The cold will help to reduce the likelihood of triggering these slabs, but we remain wary of steep terrain near ridge crest, convex rollers and other spots that appear to be fat and wind loaded.

Problemi valanghivi

  • Wind Slabs

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

    Wind slabs on south facing aspects are the most likely to be remain sensitive to human triggering Tuesday. Moderate to strong wind out of the west/northwest began to pickup Saturday night and continued into Sunday forming fresh slabs, even at lower elevations. The cold temperatures will likely lessen their sensitivity to human triggering, but it's sounding like soft snow is hard to come by at the moment.

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely - Possible
    Dimensione
    2–3

    This layer is becoming more deeply buried and somewhat harder to trigger. But it would likely result in a large avalanche if you tickle it from the wrong spot. Most likely trigger points are areas where the snowpack is shallow or variable so avoid fat to thin transitions and stick to places where the snowpack is deep. Remote triggering is possible and a cornice fall or surface avalanche could set off a deeper slide so be aware of your overhead exposure. Decreasing temperatures will initially make it harder to trigger this problem but if the cold persists, the failure layer will become weaker and we may eventually see sensitivity creeping up again in the coming days

Confidence

Low - Uncertainty is due to the extreme variability of wind effect on the snowpack. Uncertainty is due to the limited number of field observations.

Weather Forecast

MONDAY NIGHT: Clear, overnight low temperature around - 30 C, light southwest wind, no new snow expected.

TUESDAY: Broken cloud cover, daytime high temperature around -22, light south wind, no snow expected.

WEDNESDAY: Broken cloud cover, daytime high temperature around -20, light west wind, no snow expected during the day, trace of snow possible Wednesday night.

THURSDAY: Clear skies, daytime high temperature around -22, moderate to strong northwest wind at upper elevations, no snow expected.

Avalanche Summary

No recent avalanche observations to report, it's possible natural wind slab avalanches may have failed during the wind event over the weekend.

Explosive control earlier in the month produced many large avalanches that failed on the weak sugary crystals at the bottom of the snowpack. These avalanches ran full path.

On December 1, a size 2.5 avalanche was remotely triggered by a recreational group on Log Cabin. This avalanche likely failed on the weak, sugary snow at the bottom of the snowpack. 

Natural avalanche activity and human triggered avalanches will be most likely in wind-loaded features anywhere recent winds have redistributed the snow. Triggering the deep layer (see the December 1 avalanche described above) is most likely to occur in shallow areas or where the snowpack variable in depth with a mix of shallow and deep zones. 

Snowpack Summary

Northerly winds have gotten into almost all the terrain of the White Pass, even down into the trees at lower elevations. Big thanks to the party who submitted this MIN on Sunday! Lots of shooting cracks were observed as they were out in the Fraser Chutes. Wind slabs are expected to be the principle problem, and It is likely getting pretty hard to find snow that is not wind effected.

The middle snowpack is supportive to travel but snow depth still varies greatly with aspect and elevation. 

A layer of weak, sugary snow at the base of the snowpack has been observed in most areas. This layer was reactive earlier in December, and it might still be possible to trigger this deeply buried layer in shallow snowpack areas or if a cornice fall or surface avalanche impacts a slope. If triggered, this basal layer could produce large avalanches. This sugary layer will likely become weaker in the coming days with cold temperatures potentially making it increasingly sensitive to triggering.

Terrain and Travel

  • Keep your guard up at lower elevations. Wind slab formation has been extensive.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • Be aware of the potential for large avalanches due to the presence of a deep persistent slab.

Regioni coperte