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Avalanche Forecast

Archived

Dec 31st, 2021–Jan 1st, 2022

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

Regions

Yukon.

Choose mellow slopes out of the wind to find the best riding and the lowest avalanche hazard. New snow and south winds are likely building reactive windslabs. Constantly assess local conditions, recent snowfall amounts have varied across the region.

Confidence

Moderate - Forecast snowfall amounts are uncertain. Recent weather patterns have resulted in a high degree of snowpack variability within the region.

Weather Forecast

FRIDAY NIGHT: Mostly cloudy. 5-15 cm of snow expected. Strong south winds trending to extreme southwest at higher elevations. Temperature at 1500 m around -13 C.

SATURDAY: Mostly cloudy. 5-10 cm of snow expected. Light Southwest winds, with a switch to northerly outflow winds at lower elevations in the evening. Temperature at 1500 m dropping to around -15 C.

SUNDAY: A mix of sun and cloud. Around 5 cm of snow expected overnight, with another 0-2 cm through the day. Strong northeast winds, trending to southeast at higher elevations. Temperature at 1500 m between -20 C and -25 C with a possible temperature inversion. 

MONDAY: A mix of sun and cloud. Possible trace of snow expected. Strong northeast winds trending to southeast at higher elevations. Temperature at 1500 m below -25 C, with a possible temperature inversion.

Avalanche Summary

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

If you are out in the mountains, and have information to, or even just good vibes and good photos to share, please consider making a quick post on the Mountain Information Network.

Snowpack Summary

By Saturday morning, we expect to see 10-25 cm of new snow in a 24 hour period. The forecasted strong southerly wind is likely building reactive windslabs in leeward terrain.

Here and here are two great Mountain Information Network (MIN) posts about conditions on Thursday in the White Pass area.

On Wednesday, the region received about 5 to 15 cm of new snow, with the higher amounts being in the Wheaton area. Switching winds (southerly then northerly) redistributed this snow over old surfaces such as sastrugi, wind slabs or 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 a larger wind slab 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.