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Avalanche Forecast

Archived

Dec 17th, 2022–Dec 18th, 2022

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

Sea To Sky, Brandywine, Garibaldi, Homathko, Powell River, Spearhead, Tantalus, Sasquatch, Tetrahedron.

Danger ratings have decreased but concern still remains for deeper weak layers and wind loaded features.

Maintain your awareness as you transition through aspects and elevations.

Confidence

Moderate

Avalanche Summary

Over the last 3 days, activity has been limited to small human triggered slabs specific terrain features, mostly on west facing slopes.

During the storm last Friday, explosive control produced persistent slab avalanches that failed on the mid-Nov crust down about 50cm. No avalanches have been reported on this layer since - however it remains a concern.

If you head out into the mountains, please share your photos or observations on the Mountain Information Network. Your information helps us understand local conditions!

Snowpack Summary

Pockets of wind slabs have developed from northerly winds at higher elevations, sitting over a thin crust. On north facing slopes, dense wind pressed snow can be found.

Two weak layers of concern sit in the snowpack:

  • A layer of surface hoar from early December is buried 30-50 cm deep below wind affected snow. This layer can be found in sheltered and shaded terrain features.

  • A widespread crust and facet layer from late November is buried 40-80 cm deep, found on all aspects and elevations.

Total snow depths remain low for December with 90 to 140 cm at treeline and up to 200 cm in the alpine. Much of the below treeline elevation band is below the threshold for avalanches.

Weather Summary

An Arctic front dominates the weather over BC. Light snowfall is expected Saturday night as a low south of Vancouver Island briefly competes with the cold air.

Saturday Night

Mainly cloudy with isolated flurries bringing up to 4 cm of snow. Freezing level at valley bottom. Moderate to strong northwest winds.

Sunday

A mostly cloudy day with another 5 cm possible, with heavier accumulations possible in Garibaldi Park. Moderate southwesterly winds. Alpine high of -15°C, freezing level below valley bottom.

Monday

Mostly cloudy with moderate westerly winds. Temperatures drop further, expect a high of -20°C. Isolated flurries.

Tuesday

A mix of sun and cloud with moderate to strong westerly winds. Light to moderate snowfall. Freezing level below valley bottom. Alpine highs of -20 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Wind slabs are most reactive during their formation.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.