Bollettino valanghe

Lizard-Flathead

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

Pericolo valanghe

Fri
Sat
Alta quota
4 · Forte
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
Apri la mappa completa

In sintesi

Up to 35 cm by the end of the day Wednesday combined with wind and the freezing level rising to 1800 m bring the avalanche hazard to HIGH in the alpine. There is uncertainty whether deeper weak layers will become more reactive, resulting in large and destructive avalanches.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3.5

    A persistent slab problem formed by a crust down 100-270 cm has created a low likelihood, high consequence scenario that is difficult to forecast. There has been an increase of avalanche reports on this layer recently. It is uncertain how the forecast warm temperatures will affect the snowpack and if we will see more activity on this layer during the warm period. 

    Avoid likely trigger spots such as steep, rocky slopes with a shallow or thin to thick snowpack. Large additional loads like small avalanches or failed cornices can trigger deeper weak layers. The same feature or path can slide repeatedly when the persistent weak layer is reloaded with new snow. 

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    1.5–2.5

    10-20 cm new snow are forecast by Wednesday morning and another 5-10 cm during the day. The snow will fall with warm temperatures forming cohesive storm slabs. Moderate to strong southwest wind will redistribute the new snow developing fresh wind slabs. 

    Expect to find more reactive deposits around ridge features. Be especially mindful around steep and convex openings in the trees. The new and recent snow may overlie a weak interface which could result in deeper and touchier than expected slabs. Smaller avalanches might step down and trigger deeper weak layers resulting in large and destructive avalanches.

Confidence

Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

Tuesday night: Cloudy, 10-20 cm new snow, moderate to strong southwest wind, treeline low around -3 °C, freezing level around 1400 m.

Wednesday: Cloudy, 5-10 cm new snow and rain at lower elevations, moderate southwest wind, treeline high around +1 °C, freezing level rising to around 1800 m.

Thursday: Sunny with increasing cloud coverage, up to 3 cm new snow, moderate southwest wind, treeline high around +1 °C, freezing level rising to 2200 m.

Friday: Mix of sun and cloud, trace of new snow, light southwest wind, treeline high around -2 °C, freezing level around 1400 m.

Avalanche Summary

On Monday, now new avalanches were reported.

On Sunday, a few natural cornice failures resulting in size 2.5 avalanches were observed as well as a natural size 2 slab avalanche. 

On Saturday, storm slab avalanches up to size 2.5 were triggered by explosives. Overnight, a large (size 3.5) natural storm slab avalanche released and a large (size 2.5) cornice failure occurred. 

On Friday, storm slab avalanches released naturally up to size 2.5. Explosives triggered storm slabs to size 2.5, and skiers triggered avalanches to size 2. A large (size 2) natural cornice failure was reported likely having failed in the overnight storm.

The persistent slab problem has produced sporadic and spotty activity in the Lizard-Flathead and nearby regions. 

  • On Monday, a large size 3 deep persistent slab released naturally in the neighbouring Waterton National Park. The avalanche was more than 2 m deep.
  • On Sunday, a very large (size 4) persistent slab avalanche that released naturally in the neighbouring Waterton National Park was observed. The avalanche released at an elevation of 2000 m on an E-NE aspect. Large avalanches (up to size 3.5) were reported in the Fernie area with the early December layer as suspected bedsurface. The avalanches likely ran during the storm on Friday or Saturday.
  • Last Wednesday, two size 3 persistent slab avalanches were reported. They released at an elevation of 1800 m and 2000 m on an E aspect and were 2 m deep. Most likely they released during the storm before the New Year. 
  • Last week on Sunday, a size 2.5 persistent slab avalanche was triggered on an E aspect at treeline. This avalanche is detailed in a MIN post and features in our latest blog post, Photos of recent persistent slab avalanches in the southern interior.

Snowpack Summary

The recent storm snow totals 40-50 cm. In open terrain and upper elevations, wind developed more reactive deposits around lee and convex features. This recent snow covered a hard, faceted snow surface which formed during cold temperatures and may take a little time to bond. 

The most notable layer of concern in the snowpack is a crust that was formed in early December and is now down 100-270 cm. Activity on this layer has been sporadic, the most recent persistent slab avalanche in the region was reported on January 9. This layer has created a low likelihood, high consequence scenario which is best managed through conservative terrain choices and disciplined backcountry travel techniques.

Terrain and Travel

  • Extra caution for areas experiencing rapidly warming temperatures for the first time.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
  • Caution around slopes that are exposed to cornices overhead.

Regioni coperte