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Avalanche Forecast

Archived

Dec 21st, 2020–Dec 23rd, 2020

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 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.

Seek out the sheltered, lower angle snow now that the winds have reworked the upper snowpack. Another round of strong wind and new snow for Wednesday should give wind slab hazards a refresh.

Confidence

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

Weather Forecast

MONDAY NIGHT: Thin cloud cover. Light southwest winds increasing in the morning.

TUESDAY: Cloudy with isolated flurries. Moderate southwest winds, increasing over the day and evening. Alpine high temperatures around -9.

WEDNESDAY: Cloudy with increasing flurries bringing about 10 cm of new snow. Moderate to strong south winds. Alpine high temperatures around -5.

THURSDAY: Cloudy. Light southwest winds. Alpine high temperatures around -8.

Avalanche Summary

Reports of avalanche activity in the region are still limited, but two large (audible) natural slides were noted on Saturday by the Yukon field team as they performed snowpack observations near the summit of White Pass. 

With strong southerly winds having replaced recent exceptional powder riding with a new array of wind slabs over the terrain, human triggered slabs are once again the primary concern.

The most likely place to trigger an avalanche is on the leeward (think north through east) side of ridges and ribs where new wind slabs were formed.

Snowpack Summary

Snowpack is 200 cm in Whitepass, closer to 100 cm in drier areas like the Wheaton.

Eight to ten hours of moderate to strong southwest winds overnight Friday & early Saturday morning resulted in widespread wind scouring and loading, forming wind slabs and cornices in the process. These hazards are likely to remain sensitive to human or machine triggers over the next few days.

Below this surface snow lies a widespread melt-freeze crust. The crust has been reported up to 1400 m in the Wheaton Valley, up to 1800 m near the Alaska border. 

The lower snowpack is generally settled and strong after a massive storm at the beginning of December. However, there is potential for weak snow at the bottom of the snowpack in colder drier areas such as the Wheaton Valley. 

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Avoid terrain traps where the consequence of any avalanche could be 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.