Avalanche Forecast

Archived

Dec 27th, 2021–Dec 28th, 2021

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Below Threshold.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Below Threshold.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Below Threshold.

Regions

Yukon.

Make conservative decisions and avoid wind loaded features. The new wind slab likely won't bond well to the surfaces below.

Confidence

Moderate -

Weather Forecast

Monday night: no new snow expected. Low of -14 at 1200m with moderate to strong northwest winds. Possibility of temperature inversion with colder temperatures in the valley bottom.

Tuesday: skies clearing in late afternoon and no new snow expected. winds will be moderate from the northwest with a high of -15 at 1200m.

Wednesday: A mix of sun and cloud with the possibility of some light flurries. Strong northwest wind. High of -10 at 1200m.

Thursday: clear with no new snow expected. Moderate northwest winds with a high of -18 at 1200m.

Avalanche Summary

We suspect that some natural wind slab avalanches would have released on Monday morning.

On Wednesday our field team observed several natural avalanches up to size 2 on Log Cabin and above Fraser Chutes. These avalanches were on cross-loaded east and south east facing slopes above treeline.

Snowpack Summary

up to 15cm of new snow has formed wind slab on south and east aspects. These new wind slabs overlie old faceted hard slab. We suspect the new wind slab will not bond well to these surfaces. North and west aspects are generally scoured.

Surface hoar may exist just below the surface at 1300m and below. It is likely only a problem where wind slab has formed above it.

The lower snowpack is made up of weak sugary snow. An avalanche at this interface is most likely to be triggered in shallow areas or with a large impact like a cornice fall or surface avalanche.

Terrain and Travel

Keep your guard up at lower elevations. Wind slab formation has been extensive.
Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.