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Avalanche Forecast

Archived

Dec 23rd, 2021–Dec 24th, 2021

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

Regions

Yukon.

Managing a hard slab on top of weak sugary snow can be tricky. Avalanches are getting harder to trigger but now is not the time to become complacent. Hard slab can be unpredictable so think in terms of consequences as you travel through terrain just in case you get surprised. 

Confidence

Moderate -

Weather Forecast

The cold continues with north winds. Protect yourself against frostbite!

THURSDAY NIGHT: partly cloudy, winds from the north up to 30km/hr gusting to 40km/hr, trace precipitation, temperature -20 C. 

FRIDAY: partly cloudy, winds from north up to 50km/hr, no new precipitation, temperature -22 C. Chance of reindeer sighting! 

SATURDAY: HoHoHo! mostly clear skies, winds from the north up to 40km/hr, no new precipitation, temperature dropping to -30 C!

SUNDAY: mostly clear in the morning skies clouding over in the afternoon, wind 20km/hr from the north changing to 20km/hr from the southwest in the afternoon, up to 5cm of new snow starting in the afternoon, temperature -30 C in the morning rising to -14 C in the afternoon.

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. 

During extreme winds on Tuesday night, a size 2 natural avalanche reached the highway during a closure. 

The most likely place we will see avalanche activity on Friday 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

Exposed alpine and treeline areas in places such as Paddy Peak and Powder Valley have been scoured to ground on north aspects and ridges. Wind impacted snow also exists well down into treeline in these places.

In the White Pass, all but sheltered, south facing slopes have been impacted by the wind. Firm wind slabs exist on south aspects and east facing gully features. Softer snow does still exist in sheltered treeline areas. 

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

  • Watch for areas of hard wind slab on alpine features.
  • Seek out wind sheltered terrain below treeline where you can avoid wind slabs and find great riding.
  • Keep your guard up at lower elevations. Wind slab formation has been extensive.
  • This avalanche problem is difficult to trigger but if so, consequences are serious.
  • 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.