Avalanche Forecast

Archived

Jan 8th, 2021–Jan 9th, 2021

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, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Sea To Sky.

It may be tempting to get into bigger terrain, however sporadic high consequence persistent slab avalanches have very recently been reported. The best and safest riding will be found in mellow wind sheltered terrain.

Confidence

Low - Uncertainty is due to unpredictable avalanche behavior.

Weather Forecast

Friday Night: Mainly cloudy, moderate to strong southerly wind, alpine high -5, freezing level 600 m.

Saturday: Mainly cloudy with sunny breaks, light south wind, alpine high -4, freezing level 1000 m.

Sunday: Mainly cloudy with flurries, moderate southwest wind, alpine high -3, freezing level 1000 m.

Monday: Flurries, moderate south wind, alpine high -1, freezing level 1200 m.

Avalanche Summary

On Thursday there was a report of a remotely triggered (from a distance of 20m) size 2.5 deep persistent slab avalanche on a west aspect at 1930 m on Cowboy Ridge. The fracture line was up to 200 cm deep. This avalanche subsequently sympathetically triggered an additional size 2.5-3 deep persistent avalanche about 50 m below on Cowboy ridge.

On Wednesday there were numerous size 2 explosives controlled storm slab avalanches reported running in the alpine and treeline. As well there were several persistent and one deep persistent slab size 2.5-3 ranging in depth from 100-150 cm.

Snowpack Summary

Over 150 cm of recent storm snow from the past week has seen extensive wind effect at upper elevations, with scoured windward aspects, wind slabs in lee features and growing cornices at ridgetop.

The snowpack is currently quite complex. The layer of greatest concern is a melt-freeze crust from early December, found around 100-200 cm deep in the snowpack. This crust may have surface hoar or sugary faceted grains sitting above it. There have been several recent large natural and human triggered avalanches on this layer and new snow loads as well as large loads from storm slab avalanches have potential to trigger these layers.

Terrain and Travel

Be especially cautious as you transition into wind affected terrain.
Be mindful that deep instabilities are still present and have produced recent large avalanches.
Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
Cornice failure may trigger large 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.