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Avalanche Forecast

Archived

Mar 6th, 2020–Mar 9th, 2020

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

Regions

Yukon.

Thursday's extreme wind event significantly altered the landscape. Although spotty, hard wind slabs can be found at all elevations. Travel may be challenging, especially in the alpine. Hard wind slabs are difficult to trigger, but once triggered can produce very large avalanches.

Confidence

Low - Uncertainty is due to the limited number of field observations. Uncertainty is due to the extreme variability of wind effect on the snowpack.

Weather Forecast

The calm before Sunday’s storm.

FRIDAY NIGHT: Light southwest wind, freezing level at valley bottom, no significant precipitation expected.

SATURDAY: Scattered cloud cover, light to moderate southwest wind, freezing level at valley bottom, no significant precipitation.

SUNDAY: Broken cloud cover, strong south/southwest wind, 2 to 6 cm of snow possible during the day, 5 to 10 cm possible Sunday night.

MONDAY: Broken cloud cover, moderate to strong southwest wind, freezing level at valley bottom, 5 to 10 cm of snow possible.

Avalanche Summary

We received reports of natural avalanches reaching the Klondike highway during the wind event and start zones were reloading Thursday. Our field team got out to survey the damage from the wind event Friday, their detailed observations can be found here.

Snowpack Summary

The extreme wind event delivered wind from a variety of directions, but the main push was done by north (outflow) wind. This event has resulted in new wind slab formation in open terrain at all elevations. The distribution, size and depth of slabs from this event is highly variable. There may be wind loaded snow in areas we traditionally think of as sheltered.

At White Pass the snowpack is roughly 200 cm thick with a strong mid and lower snowpack. Thin snowpack areas further inland may have a shallower snowpack composed of sugary faceted grains. Lower elevations have a melt freeze crust near the surface.

Terrain and Travel

  • Watch for areas of hard wind slab on alpine features.
  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
  • Seek out sheltered terrain where new snow hasn't been wind-affected.

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.