Avalanche Forecast

Archived

Dec 30th, 2021–Dec 31st, 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 possible, human triggered probable.

Below Treeline

Below Threshold.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Below Threshold.

Regions

Yukon.

Shifting wind (again) means reverse and cross-loading developing. Back off slopes if you see 30 cm or more of recently wind-loaded snow. Variable snowpack conditions exist throughout the region.

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack. Recent weather patterns have resulted in a high degree of snowpack variability within the region.

Weather Forecast

An arctic ridge of high pressure will re-establish briefly, leading to another clear and cold day heading into Friday. As a strong system will quickly intensify over the Gulf of Alaska, very strong winds will develop ahead of the front. Moderate snowfalls amounts are expected for the weekend.

THURSDAY NIGHT: Clear / Moderate northwest winds in the alpine / High of -18

FRIDAY: Flurries all day / Strong southwest winds in the alpine / High of -14

SATURDAY: Snow ~10-15 cm / Strong southwest easing off during the day / High of -12

SUNDAY: Snow ~ 10 cm / Moderate north winds / High of -25

Avalanche Summary

Several wind slabs avalanches (size 1) reaching the highway were reported on Wednesday afternoon.

If you are out in the mountains, please consider filling out a Mountain Information Network report.

Snowpack Summary

On Wednesday, the region received about 5 and 15 cm of new snow, with favoured amounts in the Wheaton area. Switching winds (southerly then northerly) have redistributed the new snow which now covers old surfaces such as sastrugi, old wind slabs or recently scoured slopes in the alpine.

At treeline, the wind also affected the surface, but pockets of powder can be found between cross-loaded features. Underneath this wind-affected snow, there is a thick layer of weak snow (faceted grains).

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

Recent wind has varied in direction so watch for wind slabs on all aspects.
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.

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.