Bollettino valanghe

Kootenay Boundary

Dec 24 – 25, 2022Avalanche Canada
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Archiviato · scaduto 4 years ago

Pericolo valanghe

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

In sintesi

Stick to conservative terrain as the storm slab problem becomes trickier on Saturday, moderate to heavy snowfall is expected.

With several buried persistent weak layers expected to become more reactive as snowfall accumulates, step down avalanches are increasingly likely.

Problemi valanghivi

  • Persistent Slabs

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

    There are three persistent weak layers of concern buried in the snowpack, see the Snowpack Summary for more details.

    Layers of surface hoar can be found in shaded and wind sheltered terrain features primarily at treeline and low alpine elevations, while crusts can be found on sun affected slopes. These layers are most concerning on large open slopes where wide propagation could produce large avalanches.

    Small avalanches have the potential to step down to these deeper layers. As snowfall accumulates, these layers may become more reactive to human triggers.

  • Storm Slabs

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

    Fresh snow and strong winds will develop new and reactive slabs. Expect winds to redistribute snow at treeline and alpine elevations into deeper and more reactive slabs in wind loaded features.

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

Terrain and Travel Advice

  • Watch for fresh storm slabs building throughout the day.
  • Use increased caution at all elevations. Storm snow is forming touchy slabs.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Be aware of the potential for larger than expected storm slabs due to the presence of buried surface hoar.

Confidence

Moderate

Avalanche Summary

A cycle of natural wind slab avalanches to size 1.5 was observed on Thursday morning, driven by the moderate to strong southeast winds. Two size 2 skier accidentals were also reported in north facing wind affected features, failing on the mid December surface hoar. Read about their decision making after triggering the first avalanche here.

On Tuesday and Wednesday several size one skier triggered wind slab avalanches were reported. These avalanches were on easterly aspects at upper treeline.

Snowpack Summary

The snowpack is becoming increasingly complex with several deeper instabilities that may persist through the season. Sustained cold temperatures have continued to facet (weaken) the snowpack.

At the surface, storm snow is being redistributed into wind loaded features in treeline and alpine terrain. These new slabs will form over facets, surface hoar or a crust.

Several more layers of concern exist in this snowpack:

  • An early December layer of surface hoar in sheltered areas and a thin sun crust in open south-facing terrain is buried approximately 30-50 cm deep. This layer has recently produced surprising avalanches in upper treeline and lower alpine terrain features.

  • The most concerning layer buried in mid November is made up of large surface hoar crystals, facets, and a melt-freeze crust and can be found up to 80 cm deep. This layer has been reactive at treeline between 1700 to 2200 m, on all aspects.

Weather Summary

Cold arctic air begins to weaken and move out of the area on Saturday, as a warm Pacific low pushes moderate snowfall and strong winds into the interior this week.

Friday Night

Cloudy with up to 5cm of new snow expected. Moderate southwest winds continue overnight. Freezing level below valley bottom.

Saturday

Stormy with 15-30 cm of new snow expected, favoring terrain south of Nelson and the Valhallas. Strong southwest winds and a high of -12°C.

Sunday

Cloudy with trace amounts of new snow expected. Moderate northwest winds with a high of -10°C.

Monday

Moderate to heavy snowfall returns. Temperatures warming to or above 0°C as freezing levels rise to 800 m.

More details can be found in the Mountain Weather Forecast.

Regioni coperte