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Avalanche Forecast

Archived

Dec 21st, 2020–Dec 22nd, 2020

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

Regions

Sea To Sky.

The recent snow has formed new slabs. It has also loaded weak layers that are at a prime depth for riders to trigger them.

Confidence

High -

Weather Forecast

MONDAY NIGHT: Clear skies, 40 km/h north wind, alpine temperature -11 C.

TUESDAY: Clear skies, 10 to 30 km/h north wind, alpine temperature -11 C.

WEDNESDAY: Mix of sun and cloud, 10 to 20 km/h southwest wind, alpine temperature -2 C, above-freezing layer forming around 2000 m.

THURSDAY: Clear skies, 20 km/h south wind, alpine temperature 2 C, freezing level 2200 m.

Avalanche Summary

Many wind and storm slab avalanches were triggered naturally, by riders, and explosives on Sunday. They were generally large (size 2) and occurred at all elevation bands.

The latest confirmed avalanche on the weak layers described in the snowpack summary was December 19, where a few large avalanches were triggered by riders and explosives. They occurred on northerly aspect in alpine terrain (2100 m) and were generally 30 to 50 cm deep.

Snowpack Summary

Around 20 cm of snow fell on Monday with strong northerly wind. Wind slabs may linger at treeline and alpine elevations on all aspects due to wind starting from the south and shifting to the north. In sheltered terrain, numerous storm snow interfaces may be found in the top 50 cm of the snowpack, which may take a couple of days to bond.

Two concerning weak layers are present in the snowpack. The shallower layer, being around 50 to 80 cm deep, includes feathery surface hoar crystals. There is uncertainty in the distribution of this layer, but the most likely place to find it would be in terrain features sheltered from the wind around treeline and lower alpine elevations. The more widespread weak layer includes sugary faceted grains that overlies a hard melt-freeze crust. This layer is generally found around 50 to 100 cm deep and is widespread up to around 2000 to 2200 m.

The remainder of the snowpack is well-settled.

Terrain and Travel

  • Be careful as you transition into wind affected terrain.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

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.