Avalanche Forecast

Archived

Dec 25th, 2021–Dec 26th, 2021

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Below Threshold.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Below Threshold.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Below Threshold.

Regions

Yukon.

Wind slabs remain the chief concern. Keep your guard up at lower elevations where wind slabs may be sitting over a weak layer.

Confidence

Moderate -

Weather Forecast

Saturday night: Partly cloudy. Light to moderate northwest wind. Alpine temperature around -22 C.

Sunday: A mix of sun and cloud. Light to moderate northwest wind. Alpine temperature rising to -15 C at through the day.

Monday: Overnight flurries up to 8 cm then clearing. Strong northerly wind. Alpine temperature around -10 C.

Tuesday: A mix of sun and cloud. Strong northerly wind. Alpine temperature around -13 C.

Avalanche Summary

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.

The most likely place we will see avalanche activity will be on south through east facing slopes where wind slabs have not yet bonded well to the layer below due to cold temperatures.

Snowpack Summary

Surfaces are extensively wind effected throughout the region. Exposed windward alpine and treeline terrain has been scoured to ground in places such as Paddy Peak and Powder Valley, with wind affected snow found well down into treeline. In the White Pass, firm wind slabs exist on south aspects and east facing gully features. Softer snow may still exist in sheltered treeline areas.

Surface hoar exists 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.
Watch for areas of hard wind slab on alpine features.
Avoid slopes that sound hollow or drum-like.
Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

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.