Avalanche Forecast

Archived

Dec 22nd, 2021–Dec 23rd, 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.

It is easiest to trigger avalanches in areas that look deep with heavy surface snow. Cold temperatures can make wind slabs last longer than usual.

Confidence

Moderate - Uncertainty is due to limitations in the field data.

Weather Forecast

Winds decreasing but still moderate at ridge top. The cold continues!

WEDNESDAY NIGHT: Overnight low temperature -22, moderate north wind, strong at ridge top. Mostly clear. No new snow expected.

THURSDAY: Mostly clear, daytime high temperature around -21, Light variable wind at valley bottom, strong north wind at ridge top, possible flurries to 2cm

FRIDAY: Broken cloud cover, daytime high temperature around -21, moderate to strong north/northwest wind, no new snow

SATURDAY: mostly clear, daytime high temperature around -31, moderate north wind, no snow expected.

Avalanche Summary

On Wednesday our field team observed several natural avalanches up to size 2 in the White Pass on east and southeast aspects in the alpine and treeline.

This MIN from Monday reported shooting cracks and other signs of instability in Fraser Chutes at treeline.

Snowpack Summary

10-20cm of recent snow has been heavily re-distributed by strong north winds. These fresh wind slabs will be touchy at first and cold temperatures can keep them sensitive for longer.

On the weekend two MIN reports here & here mention surface hoar at and below 1300m, which could be buried just below the recent windslab.

The middle snowpack is supportive to travel but snow depth still varies greatly with aspect and elevation.

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

Be aware of highly variable recent wind loading patterns.
If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
Stay off recently wind loaded slopes until they have had a chance to stabilize.

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.