Bulletin d’avalanche

Northwest Coastal

Jan 19 – 21, 2020Avalanche Canada
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Archivé · expiré 7 years ago

Danger d’avalanche

Tue
Wed
Alpin
4 · Fort
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
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Points saillants

The storm has produced 20 to 65 cm of new snow across the forecast region which rests on a mix of facets and old wind slabs. Conditions will likely remain touchy Monday, stick to simple terrain and avoid overhead hazard as the snowpack adjusts to all the new snow.

Problèmes avalancheux

  • Storm Slabs

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

    As of Sunday afternoon the storm has produced 20 to 65 cm of new snow and 10 to 20 cm of snow is expected Sunday Night. At upper elevations this snow rests hard old wind slabs. Out of the wind in more protected features the storm snow rests on up to 20 cm of facets formed during last weeks bitterly cold temperatures. Continued wind generally out of the south is likely forming fresh sensitive slabs in upper elevation features.

  • Deep Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely - Possible
    Taille
    3–4

    This storm is a good test for the mid November crust that lurks at the base of the snowpack. Reports of avalanches on this layer have been few and far between but it has produced large natural avalanches that seem to be most prevalent on alpine lee and cross loaded slopes.

Confidence

Low - Uncertainty is due to the limited number of field observations. Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

While the rest of the province heats up, our region should stay cool through the forecast period. The storm will continue to hammer the region through Monday afternoon before a brief break in the action Tuesday. The longer term models show another series of storms starting up Wednesday night that continue through next weekend.

SUNDAY NIGHT: Freezing level around 300 m, strong southwest wind, 8 to 20 cm of snow possible.

MONDAY: Overcast, freezing level around 500 m, moderate southwest wind, 5 to 12 cm of snow possible.

TUESDAY: Scattered cloud cover, freezing level around 400 m, light southerly wind, no significant snowfall expected.

WEDNESDAY: Overcast, freezing level around 500 m, moderate to strong south wind, trace of snow possible during the day.

Avalanche Summary

Observations on Saturday were likely hindered by limited visibility, but there were some natural and human triggered soft slab avalanches up to size 1 that were reported with crowns up to 30 cm in depth. 

Control work Friday produced avalanches to size 3 on northwest , north, northeast and east facing slopes between 1900 and 2200 m.

Reports of deep persistent slab avalanches have been trickling in throughout the month. They are associated with a November crust layer near the base of the snowpack which has produced very large avalanches (size 3+) with crown depths of around 2 m. Observations are typically in alpine terrain, on lee or cross-loaded slopes. 

Snowpack Summary

As of Sunday afternoon the storm had produced about 20 to 65 cm of snow with the larger totals in the south of the region.

The new snow is resting on extensively wind affected surfaces at and above treeline. In sheltered locations at and below treeline the new rests on up to 20 cm of facets formed during the cold temperatures of last week.  

A deep crust from mid November lurks at the base of the snowpack. A couple of recent large avalanches have run on this layer on lee and cross-loaded features high in the alpine. As this storm applies significant new snow loads to the snowpack, these deep layers will feel the stress and we may see some very large avalanches in high places.

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Don't let the desire for deep powder pull you into high consequence terrain.
  • Be aware of the potential for large avalanches due to the presence of a deep persistent slab.

Régions couvertes