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Avalanche Forecast

Archived

Dec 30th, 2023–Dec 31st, 2023

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, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

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

Fresh snow rests on a problematic persistent slab at treeline and above.

Use caution anywhere the snowpack is thin and/or variable.

Confidence

Moderate

Avalanche Summary

On Saturday, isolated storm slabs (size 1) were triggered by explosives in lee terrain near Whistler. On Friday, very large persistent slabs (up to size 3) were naturally triggered on Decker Mountain and Panorama Ridge in Whistler, with wide propagation from shallow rocky alpine northern slope. These avalanches involved up to 100-120 cm deep persistent weak layers that resulted in wide propagations.

Snowpack Summary

Up to 15 cm of new snow may sit over a recent thin melt-freeze crust up to 2000 m. Underneath, 65 and 130 cm of soft snow and heavily wind-affected snow overlies a layer of poorly bonded crusts and surface hoar. These have shown sensitivity to natural and remote triggers over the last 3 days. The lower snowpack is strong and bonded.

The snowpack at treeline has been saturated, and a surface crust may form soon with upcoming cooling. Total snow depths remain below average, with 60 to 80 cm at treeline.

Weather Summary

Saturday Night

Cloudy with isolated flurries, trace accumulation, alpine wind southwest 30 km/h, treeline temperature around 0 °C, freezing level around 1300 m.

Sunday

Mix of sun and clouds with isolated flurries, trace accumulation, alpine wind west 20 km/h, treeline temperature around -2 °C, freezing level at 1200 m.

Monday

Mostly sunny, no precipitation, alpine wind southeast 20 to 40 km/h, treeline temperature around -3 °C, freezing level at valley bottom.

Tuesday

Cloudy, 3-5 cm of snow, alpine wind southeast 30 to 50 km/h, treeline temperature around -3 °C, freezing level at valley bottom.

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.
  • Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
  • Avoid shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.

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.