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Avalanche Forecast

Archived

Feb 20th, 2023–Feb 21st, 2023

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

Regions

Northwest Inland, Kispiox, Microwave-Sinclair, Ningunsaw, South Bulkley, South Bulkley, Telkwa.

Fresh reactive wind slabs are expected to form throughout the day as northeasterly winds redistribute yesterday's storm snow.

Avoid wind-loaded slopes and be especially cautious in shallow snowpack areas where triggering a deep persistent slab remains possible.

Confidence

Moderate

Avalanche Summary

No significant avalanches were reported in the past few days but observations have been limited.

Looking forward to Tuesday, we expect fresh, reactive wind slabs to form in a reverse loading pattern and at lower elevations than you might typically expect. These wind slabs may be particularly reactive where they overlie a crust.

One natural size two deep persistent slab was reported last Thursday in the northern part of the region. It was on a northeast aspect in the alpine. Deep persistent slab avalanches like this one continue to be reported at least once a week in shallow snowpack areas.

Snowpack Summary

Up to 30 cm of new snow arrived on Monday. Northeasterly winds are expected to redistribute this new snow into fresh, reactive wind slabs.

Several layers of facets, crusts or surface hoar can be found in the top 1.5 meters of the snowpack.

In shallow snowpack areas layers of facets from November and December are near the bottom of the snowpack and have likely been responsible for some large avalanches.

Weather Summary

Monday night

Mainly cloudy with scattered flurries, trace to 5 cm accumulation. Alpine temperatures drop to a low of -16 °C. Ridge wind northeast 25-50 km/h. Freezing level at valley bottom.

Tuesday

Sunny with cloudy periods. Alpine temperatures reach a high of -16 °C. Ridge wind northeast 20 km/h gusting to 45 km/h. Freezing level at valley bottom.

Wednesday

Sunny. Alpine temperatures reach a high of -20 °C. Ridge wind east 25 km/h gusting to 50 km/h. Freezing level at valley bottom.

Thursday

Sunny with cloudy periods. Alpine temperatures reach a high of -22 °C. Ridge wind east 25-40 km/h. Freezing level at valley bottom.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Fresh wind slabs will likely form throughout the day, diligently watch for changing conditions.
  • Keep your guard up at lower elevations. Wind slab formation has been extensive.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Avoid areas with a thin or variable snowpack.

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.