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Avalanche Forecast

Archived

Dec 15th, 2022–Dec 16th, 2022

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

Regions

Sea To Sky, Brandywine, Garibaldi, Homathko, Spearhead, Sasquatch.

Buried weak layers may be more reactive as temperatures rise over Thursday night and Friday.

Continue to be conservative with terrain choices, stick to simple slopes watch for signs of instability.

Confidence

Moderate

Avalanche Summary

On Wednesday, a natural size 2 wind slab avalanche was reported. As northerly winds are expected to continue, natural and rider triggered wind slabs remain possible.

During the storm last Friday, natural and skier triggered avalanches were reported to size 2. Explosive control produced persistent slab avalanches that failed on the mid-Nov crust down about 50cm.

Over the weekend, many riders in the Squamish and Whistler area were surprised by size 1-2 slab avalanches. These slabs mainly occurred on wind-loaded slopes on north and west aspects in the alpine and treeline.

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. Expect rising temperatures will break down the surface snow on all aspects, creating a widespread crust below 2500 m once the cooling trend begins on Friday evening.

A layer of surface hoar from early December is buried 30-50 cm deep below more wind affected snow. This surface hoar remains a concern, preserved in shaded and sheltered terrain features.

The primary concern within the snowpack is a crust buried in late November, with weak facets sitting above. Professionals are concerned about the possibility of avalanches releasing at this deeper interface with the new snow load and warm temperatures.

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

Thursday Night

Clear skies. Moderate northerly winds. An above freezing layer of air sits around 1500-2000 m,

Friday

Clear skies. Alpine temperatures reach a high of 3 °C. Moderate northwest winds. An above freezing layer of air sits around 1500-2500 m.

Saturday

Mainly cloudy with isolated flurries. Alpine temperatures reach a high of -5 °C. Freezing level at valley bottom. Moderate to strong northwest winds at ridgeline.

Sunday

3 cm possible overnight.

Partly cloudy with moderate westerly winds at ridgeline. Freezing level below valley bottom, alpine high of -15°C. Another 3 cm of snow possible over the day.

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.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.
  • Be aware of the potential for surprisingly large avalanches due to deeply buried weak layers.

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.