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Avalanche Forecast

Archived

Feb 19th, 2023–Feb 20th, 2023

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 possible, human triggered probable.
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, Kispiox, Microwave-Sinclair, Ningunsaw, South Bulkley, South Bulkley, Telkwa.

The south of the region will be the hotspot on Monday as heavy snowfall forms increasingly large and reactive storm slabs.

Be prepared to dial back into more conservative terrain as new snow accumulates. Be especially cautious in shallow snowpack areas where triggering a deep persistent slab remains possible.

Confidence

Moderate

Avalanche Summary

Looking forward to Monday, we expect avalanche danger to increase throughout the day as heavy snowfall forms increasingly large and reactive storm slabs.

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

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 20 cm of new snow can be expected by the end of the day on Monday. This new snow overlies last week's storm snow and wind-affected surfaces in exposed areas. Windward slopes are generally scoured or pressed with older wind slabs found on north and east aspects.

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

Sunday night

Cloudy with clear periods and isolated flurries. Alpine temperatures drop to a low of -7 °C. Ridge wind west 20 km/h gusting to 50 km/h. Freezing level at valley bottom.

Monday

Cloudy with snowfall, heavy at times, 10-20 cm of accumulation. Alpine temperatures reach a high of -6 °C. Ridge wind east 20-35 km/h. Freezing level 700 metres.

Tuesday

A mix of sun and cloud with isolated flurries. Alpine temperatures reach a high of -11 °C. Ridge wind northeast 20-40 km/h. Freezing level at valley bottom.

Wednesday

Sunny Alpine temperatures reach a high of -20 °C. Ridge wind northeast 20-40 km/h. Freezing level at valley bottom.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Watch for changing conditions today, storm slabs may become increasingly reactive.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • As the storm slab problem gets trickier, the easy solution is to choose more conservative terrain.
  • Avoid areas with a thin or variable snowpack.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.