Boletín de aludes

South Rockies

Feb 14, 2019Avalanche Canada
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Archivado · caducó 8 years ago

Peligro de aludes

Fri
Sat
Alta montaña
3 · Notable
Límite del bosque
3 · Notable
Bajo el límite
3 · Notable
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Lo esencial

Dangerous avalanche conditions are widespread. Thick storm slabs already blanket higher elevations, with lower elevations an increasing concern as new snow settles and forms slabs over weak layers at the old surface and deeper in the snowpack.

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1.5–2.5
    New snow has increased the load on a weak layer of surface hoar now buried 50-80 cm deep. This layer has been reactive to human triggers, particularly in undisturbed areas. It is best preserved in shaded, sheltered areas between 1600-2200 m.

  • Loose Dry

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely - Very Likely
    Tamaño
    1–1.5
    Loose snow avalanches remain concern for Thursday with upwards of 40 cm of new low density snow in the region. Terrain traps and careless group management can greatly increase the consequences of loose dry avalanches.

  • Storm Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely - Very Likely
    Tamaño
    1–2
    Upwards of 40 cm of new snow fell over the region by Wednesday morning. Dangerous avalanche conditions with a reactive storm slab problem is the result. Human triggering potential will persist as natural avalanche activity tapers off.

Weather Forecast

Wednesday night: Cloudy with clear periods. Light northwest winds.Thursday: Mainly sunny with cloud increasing and flurries beginning in the evening. Light southeast winds, increasing overnight. Alpine high temperatures around -9.Friday: Cloudy with increasing flurries bringing around 10 cm of new snow by end of day, continuing overnight. Light to moderate west or southwest winds. Alpine high temperatures around -12Saturday: Cloudy with easing flurries bringing around 10 cm of new snow, with new snow totals around 30 cm. Flurries continuing overnight. Light northeast winds. Alpine high temperatures around -11.

Confidence

High -

Avalanche Summary

Reports from Tuesday showed numerous loose dry and storm slab avalanches releasing within the height of new snow, upwards of 20 cm deep. These occurred naturally as well as with ski cutting and skier traffic. Consider slab depths to have roughly doubled over the intervening time. Wednesday's reports from the adjacent Fernie area showed observations of numerous large (size 2-3) natural storm slabs on north to northeast-facing features.A report from the Flathead on Monday described continued observations of large whumpfs at 1700-1800 metres. This can be attributed to collapsing of the large, weak, January 17 layer of surface hoar. Collapses of this type on a sufficiently large and steep slope can be expected to produce persistent slab releases.A social media post from the Marten area of Elk Valley on Thursday described touchy persistent slab conditions, with lots of smaller slabs releasing over the mid-January surface hoar layer. Check out the post here. Of note is the fact that this area was previously untracked, leaving the mid-January layer undisturbed.

Snowpack Summary

Up to 40 cm of new snow has buried a variable surface of heavily wind affected old storm snow at alpine and wind-exposed treeline elevations, while adding to 20-30 cm of lower density storm snow from last week in sheltered areas above 1700 metres. In these sheltered areas, this older storm snow may cover a layer of weak, feathery surface hoar crystals. Below 1700 metres, the new snow buried a thinner cover (5-10 cm) of the same storm snow that instead overlies a melt-freeze crust.The mid-January layer of surface hoar or a crust is now buried around 50 to 80 cm deep. The surface hoar is found on shaded and sheltered slopes and is most prominent between 1600 m and 1900 m but has been found up to 2200 m. The melt-freeze crust is found on south aspects at all elevations. This layer was the subject of a recent Special Public Avalanche Warning.The middle of the snowpack is generally consolidated. The bottom half of the snowpack is unconsolidated and composed of weak and sugary faceted grains.

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