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Avalanche Forecast

Archived

Jan 6th, 2022–Jan 7th, 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 possible, human triggered probable.
Below Treeline
Below Threshold.

Regions

Yukon.

Wind slabs exist on all aspects and elevations, and may remain reactive to human triggering for longer than normal where they overlie a layer of weak facets.

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

Arctic outflow continues to be the predominant weather feature but a weak disturbance on Friday should bring increased cloud cover and a chance of isolated flurries. 

Thursday Overnight: Partly cloudy with a chance of isolated flurries, moderate to strong N wind, treeline temperature around -28 °C.

Friday: A mix of sun and cloud with a chance of isolated flurries, moderate to strong NE wind, treeline high around -28 °C.

Saturday: Sunny, moderate to strong NE wind shifting to the SE, treeline high around -35 °C.

Sunday: Snowfall 5-15 cm, moderate to strong SE wind, treeline high around -30 °C.

Avalanche Summary

On Tuesday in White Pass, a natural avalanche cycle occurred as a result of northerly outflow winds forming wind slabs in an atypical, reverse-loading pattern on top of a weak layer of facets. Natural wind slab avalanches up to size 2.5 were observed from the highway corridor. This MIN report from the Avalanche Canada field team highlights the problem and include a photo of some recent natural wind slabs.

Recently formed wind slabs may remain reactive to human triggers for longer than is typical due to the weak facets (sugary snow) they are sitting on.

Snowpack Summary

On New Years Eve, the region received around 30 cm of new snow. Over the past week, strong winds shifting from southwest to northeast have redistributed this new snow into wind slabs on all aspects and has resulted in heavily wind affected surfaces on all aspects and elevations.

A weak layer of facets (sugar snow) exists underneath the new snow, formed by prolonged clear skies and cold temperatures prior to the storm. Recently formed wind slabs may remain reactive to human triggers for longer than is typical due to this weak layer they are sitting on.

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 wind slab avalanche that steps-down to these deeply buried basal facets.

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.
  • Be aware of the potential for large avalanches due to the presence of a deep persistent slab.
  • 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.