Bollettino valanghe

Northwest Inland

Feb 17 – 18, 2020Avalanche Canada
Vedi sulla mappa
Archiviato · scaduto 7 years ago

Pericolo valanghe

Wed
Thu
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
Apri la mappa completa

In sintesi

Start small and aim for areas that haven't been exposed to recent winds. The possibility for large persistent slab avalanches from suspect terrain features should factor into your terrain decisions.

Problemi valanghivi

  • Wind Slabs

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

    Consistent recent light snowfall and strong westerly winds have formed wind slabs in exposed areas, particularly in the immediate lee of ridge features. Avalanches in surface layers around steep, rocky features at ridgecrest may carry the risk of triggering a deeper weak layer. 

    Steep sheltered slopes at lower elevations may still be capable of producing storm slab releases with a trigger, particularly in parts of the region with 30 or more cm of recent snow.

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2.5–3.5

    A concerning number of large, deep and destructive avalanches have been human triggered and have ran naturally on deeply buried weak layers in the last two weeks. Large alpine features that have not yet slid need to be treated as suspect, especially if they have seen significant recent wind loading. Wind slab or cornice releases are likely triggers for this problem. Human triggering is most likely in shallow, rocky areas where the snowpack transitions from thick to thin.

Confidence

Moderate - Recent weather patterns have resulted in a high degree of snowpack variability within the region.

Weather Forecast

Sunday night: Cloudy with scattered flurries bringing up to 10 cm of new snow. Strong northwest winds. Alpine low -10 C. Freezing level valley bottom.

Monday: Mainly cloudy. Strong west winds, easing over the day. Alpine high temperatures around -8 C.

Tuesday: Mix of sun and cloud. Light southwest winds. Alpine high temperatures around -4 C.

Wednesday: Mix of sun and cloud. Moderate southwest winds, strong at ridgetop. Alpine high temperatures around -4 C.

Avalanche Summary

Reports from Saturday consisted of several human triggered storm slabs size 1-1.5 at treeline and below and a few natural (possibly cornice-triggered) slabs on north to east aspects in steep open bowls at treeline.

Reports from Friday included an observation of a large cornice-triggered wind slab in Morning Bowl - see the report here. 

During the first half of the month there were many very large and destructive avalanches failing on deeply buried weak layers near the bottom of the snowpack. The bulk of this activity occurred above treeline on north through east facing aspects, but any large alpine slopes that have not yet avalanched should be treated as suspect. A few examples of MIN reports of large events February 8-11 include Hudson Bay, Kathlyn Face, French Peak, Pine Creek Trail, and Babines.

Snowpack Summary

10-40 cm of new snow fell over the last week with greatest accumulations in the west of the region. In exposed areas, this snow is highly wind affected. At lower elevations, the recent snow overlies isolated patches of surface hoar in shady sheltered areas or crusts on south-facing slopes and below 1200 m.

A weak layer of faceted snow that formed during cold weather in mid January is buried approximately 60-120 cm below the surface. A few large avalanches were triggered on this layer in the first half of the month.

An older crust/facet layer from November, lurking at the base of the snowpack, produced many very large avalanches during the first half of the month. As a product of old, weak snow from the early season, this layer is most likely to be found at high elevations.

Terrain and Travel

  • Avoid freshly wind loaded terrain features.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
  • Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.

Regioni coperte