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Avalanche Forecast

Archived

Dec 26th, 2021–Dec 27th, 2021

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.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Below Threshold.

Regions

Yukon.

Small inputs of new snow will form fresh, thin but reactive wind slabs on Monday. Keep your guard up at lower elevations where hard older wind slabs may be sitting over a weak layer.

Confidence

Moderate -

Weather Forecast

Sunday night: Around 5 cm new snow. Moderate northwest wind. Alpine temperatures -16 C.

Monday: A mix of sun and cloud. Strong northwest wind. Weak inversion with alpine temperatures around -12 C.

Tuesday: A mix of sun and cloud. Moderate northwest wind. Alpine temperatures around -12 C.

Wednesday: A mix of sun and cloud. Strong northwest wind. Alpine temperatures around -10 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. 

Looking ahead, the most likely place we will see avalanche activity will be where new wind slabs are forming on south through east facing slopes.

 

Snowpack Summary

Small inputs of new snow blow over hard, wind hammered surfaces that have likely faceted in recent frigid temperatures. As a result, new wind slabs are expected to bond poorly to underlying surfaces. 

Previous winds have scoured exposed alpine and treeline areas 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 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

  • Wind slabs are most reactive during their formation.
  • Keep your guard up at lower elevations. Wind slab formation has been extensive.
  • 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.