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Avalanche Forecast

Archived

Jan 19th, 2020–Jan 20th, 2020

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Northwest Inland.

In the alpine 10 to 15 cm of snow rests on old wind slabs, sastrugi and wind crust. In sheltered terrain at and below treeline small shallow storm slabs were very sensitive to human triggering over the weekend, a trend that is expected to continue into Monday

Confidence

Low - Uncertainty is due to the limited number of field observations.

Weather Forecast

While the rest of the province heats up, our region should stay cool through the forecast period. Dribs and drabs of snow are expected to continue through Monday afternoon. Tuesday offers a brief break in the action before another storm system begins to impact the region Wednesday night.

SUNDAY NIGHT: Freezing level around at valley bottom, strong southwest wind, 1 to 5 cm of snow possible.

MONDAY: Overcast at dawn clearing to just a few clouds by sunset, freezing level at valley bottom, moderate southwest wind, 1 to 5 cm of snow possible.

TUESDAY: Scattered cloud cover at dawn building to overcast in the afternoon, freezing level at valley bottom, light to moderate south wind, no significant snowfall expected.

WEDNESDAY: Scattered cloud cover at dawn building to overcast in the afternoon, freezing level at valley bottom, moderate south wind, no significant snowfall expected during the day.

Avalanche Summary

On Saturday thin storm slabs up to 10 cm in depth were sensitive to human triggering at and below treeline where the new snow is resting on facets in wind sheltered terrain.

On Wednesday and Thursday, we received reports of natural and skier triggered wind slab avalanches size 1.5-2.5 around treeline. Crown depths were up to 1 m, and they ran on a surface hoar layer buried by the previous storm on January 10th. 

There have been reports from the Bulkley Valley of natural wind slab and persistent slab avalanches up to size 3. These are thought to have been failing on the crusts/facet/depth hoar interface near the ground. The last reported activity at this interface was Monday January 13th. 

Snowpack Summary

Widespread wind slabs, sastrugi and breakable wind crust can be found above 1400 m. Southerly winds and 10 to 15 cm of recent snow are likely forming fresh wind slabs in places previously scoured by northeasterly arctic outflow winds.

In wind protected features at and below treeline up to 10 cm of recent storm snow lies on top of facets which have recently been sensitive to human triggering. Surface Hoar up to 1 m in depth may also be found at treeline.

Facets, crust and depth hoar can be found near the base of the snowpack. A couple of large avalanches are suspected to have run on this interface in the last few weeks. These larger avalanches have been confined to lee and cross-loaded features in the alpine.

Terrain and Travel

  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Watch for areas of hard wind slab on alpine features.
  • Avoid open slopes and convex rolls at and below treeline where weak layers may be preserved.
  • Be aware of the potential for large avalanches due to the presence of a deep persistent slab.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.