Bulletin d’avalanche

Lizard-Flathead

Dec 27 – 28, 2022Avalanche Canada
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Archivé · expiré 4 years ago

Danger d’avalanche

Thu
Fri
Alpin
4 · Fort
Limite forestière
4 · Fort
Sous la limite
4 · Fort
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Points saillants

Temperatures and freezing levels are rising, expect that reactivity of both the wind slab and persistent weak layer avalanche problems to increase.

Recent snow and strong winds have built wind slabs at all elevations.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Very Likely
    Taille
    1–2.5

    Fresh snow and strong winds has built new and reactive slabs. Expect winds to redistribute snow at treeline and alpine elevations into deeper and more reactive slabs in wind loaded features. Where strong winds are observed slabs could be found further down slope than expected.

    Expect slabs to become very reactive as the temperatures and freezing levels rise.

    Expect slabs to be reactive as they sit over a variety of weak surfaces - facets, a crust and/or surface hoar.

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1.5–3

    Two concerning persistent weak layers can be found in the snowpack. The first is a surface hoar/crust layer from early December and the second is a surface hoar, facet or crust layer from mid November. These layers are most concerning on sheltered treeline features where surface hoar is most likely to be preserved.

Confidence

Moderate

Avalanche Summary

On Sunday reports of numerous explosive control avalanches have been submitted. Between the elevations of 2000 and 2300 m, these avalanches were mostly located on north through to east aspects, large (size 2) and within the new storm snow. Crown depths were consistent at 40 plus centimeters deep, running generally 200 meters with one running 400 meters.

One natural avalanche was reported as Very large (size 2.5) 40cm deep and running approx. 250 meters

On Thursday loose dry avalanches to size 2 were reported in steep terrain features.

A natural size 2.5 persistent slab avalanche was reported, thought to have occurred on Tuesday. This avalanche occurred on a northeast aspect, 2000 m on a reloaded bed surface.

Snowpack Summary

On Saturday 15 to 20 cm of new snow was redistributed by strong southerly winds. Larger deposits in east and north facing terrain can now be found and has formed new wind slabs. Slabs have formed over facets, surface hoar or a crust and they may not bond well.

Around 50 cm deep a layer of surface hoar at treeline and a thin crust on steep south facing slopes exists buried in early December.

The primary concern in the snowpack is the mid-November layer consisting of facets and surface hoar, buried around 80 cm deep. This layer is likely to become reactive as temperatures increase on Tuesday.

The lower snowpack presents as primarily facetted combined with depth hoar. Ice has been reported to exist at the base in a few different locations.

The snowpack in the forecast region is quite variable with snowpack depths at treeline varying from 100 cm to 200 cm.

Weather Summary

Monday Night

Cloudy with light snowfall 5 to 10 cm. Strong southwesterly winds 100 to 60 km/h . Freezing levels 500 m with an above freezing layer from 1300 to 2000 m . High temperatures of 0°C.

Tuesday

Cloudy with 5-15 cm of mixed precipitation expected. Strong southwest winds becoming moderate mid day 60- 40 km/h. Freezing levels 1000 m with an above freezing layer from 1300 to nearly 2500. High temperatures of +2°C.

Wednesday

Cloudy with light snow 1 to 5 cm. Light southwesterly wind. Freezing levels and temperatures begin to descend with alpine temperatures dropping to -6°C.

Thursday

Cloudy with light snow 1 to 5 cm. Light southwesterly wind. Freezing levels at valley bottom, alpine temperatures dropping to -9°C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Watch for fresh storm slabs building throughout the day.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.

Régions couvertes