Avalanche Forecast

Archived

Jan 11th, 2021–Jan 12th, 2021

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

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 unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

South Columbia.

Avalanche hazard will gradually rise over the day and into Tuesday night as new snow and wind form fresh wind slabs at upper elevations.

If you see more than 20 cm by the end of the day, treat avalanche danger as CONSIDERABLE at elevations with wind blowing the snow around.

Confidence

Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

Monday night: Snow, up to 5 cm, moderate to strong southwest wind, freezing level 500 m.

Tuesday: Snow, 5-15 cm, strong southwest wind, alpine high -4, freezing level 1400 m.

Wednesday: Snow overnight 10-20 cm then clearing, strong southwest wind easing to moderate, alpine high -7, freezing level 1200 m.

Thursday: Sunny, light northwest wind, alpine high -7, freezing level 700 m with a weak inversion setting up.

Avalanche Summary

Explosive work on Monday produced wind slabs up to size 1.5. Explosive cornice control work conducted on Saturday produced a size 1.5 cornice which did not trigger a heavily skied slope below, and a vehicle-triggered cornice drop tested a north facing alpine slope below, triggering a size 2 wind slab which did not step down to deeper layers.

Snowpack Summary

Small amounts of new snow fall on wind affected surfaces at upper elevations, surface hoar in wind sheltered areas and a thin crust on solar aspects. Winds are likely redistributing new snow into wind slabs and growing cornices.

A couple of persistent weak layers exist in the upper to mid snowpack:

The upper layer, found 40-80 cm down, is a spotty layer of surface hoar at treeline and below.
The lower layer, found 90-150 cm down, is widespread and can present as surface hoar and/or a crust.

Avalanche activity on these layers has dwindled since last week and snowpack tests results have been moderate to hard planar, but not showing propagation. Incoming snowfall in the forecast for this week will add additional load to these layers and may shed some light on whether they will remain a concern.

Terrain and Travel

Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
Wind slabs are most reactive during their formation.
Dial back your terrain choices if you are seeing more than 20 cm of new snow.

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.