Bollettino valanghe

Lizard-Flathead

Dec 26 – 27, 2021Avalanche Canada
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Archiviato · scaduto 5 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

Reactive storm slabs may linger as snowfall tapers through Sunday. Be aware of ongoing slab development in windy areas.

Problemi valanghivi

  • Persistent Slabs

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

    A layer of weak facets (sugary snow) can be found down 100-150 cm over a crust from early December. Large natural avalanches avalanches failing on this layer have been reported as recent as Friday, Dec 24. Additionally, some operators have reported that re-loaded bed surfaces (areas that have already avalanched this season) have become reactive with new loads, while deeper snowpack areas that did not previously avalanche remain dormant, furthering the complexity of dealing with a persistent weak layer.

  • Storm Slabs

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

    Snowfall is expected to taper through Sunday, with incoming gusty winds. Northerly winds were reported with the Christmas snow, and more reactive deposits may be in reverse-loaded terrain. Expect to find ongoing slab development in windy areas. Be mindful of initiating loose-dry sluffing in steeper, sheltered terrain.

Confidence

Moderate -

Weather Forecast

Saturday night: Ongoing flurries, another 5-10 cm. Gusty south wind. Overnight lows dropping to -28.

Sunday: Cold with isolated flurries, 5 cm. Moderate and gusty east wind. High temperature of -20. 

Monday: Cold and cloudy, with sunny breaks. Light wind and cold temperatures with a high of -19. 

Tuesday: Cold, mostly cloudy, and isolated flurries. Light southwest wind and a high temperature of -20.

Avalanche Summary

A large (size 2.5) natural storm slab avalanche was reported Saturday morning, running 900 m. Explosives also triggered storm slab avalanches size 1.5-2, noting that although low density slabs, fast moving snow was running far and entraining a lot of snow.

On Friday, 3 large (size 2-2.5) natural slab avalanches were reported, all failed on a persistent weak layer 100-200 cm deep, likely triggered by the new load of snow. Explosives also triggered large (size 2.5) storm slabs.

On Thursday, skiers and machines triggered storm slab avalanches to size 2, explosives triggered slab avalanches to size 3. Poor visibility prevented good alpine observations.

Snowpack Summary

35 cm low density snow arrived Christmas morning with light northerly winds and continued into Sunday. Storm totals have reached over 100 cm in the last week. Cold temperatures and calm wind will keep snow light and fluffy, but snow will be redistributed easily with any wind. Sluffing is to be expected in steep terrain.

The new snow may need time to settle and bond, reactive slabs have been reported within the storm snow. Reports also indicate the recent snow buried a surface hoar interface and pockets of old wind slab. 

A crust from early December is now 90-150 cm below the surface, and is found up to 2400 m. A layer of weak facets (sugary snow) has been reported above and below this crust. This is the layer of concern in our persistent avalanche problem, recent snowpack tests are generally showing hard results on this interface.

The lower snowpack consists of a variety of early-season crusts and mainly moist snow. Snowpack depths range from 100-250 cm at treeline elevations and taper quickly below 1800 m.

Terrain and Travel

  • Start with conservative lines and watch for clues of instability.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.

Regioni coperte